FreeCalypso > hg > freecalypso-sw
annotate doc/TIFFS-old-description @ 560:85562a6b6356
gsm-fw/L1/dsp/leadboot.c: import from the LoCosto source
author | Michael Spacefalcon <msokolov@ivan.Harhan.ORG> |
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date | Mon, 04 Aug 2014 21:43:47 +0000 |
parents | 4eeab025b502 |
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doc/TIFFS-old-description: the original description from SE 52 Mes 16
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1 The description of TIFFS that follows was originally written in the summer of |
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2 SE52 (A.D. 2013), before the major TI source discoveries which happened later |
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3 that year. The text following the dividing line below has not been edited in |
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4 content since it was written; for a newer write-up based on the current source- |
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5 enabled understanding and reflecting the current FreeCalypso plans with respect |
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6 to this FFS, see TIFFS-Overview. |
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7 |
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8 ------------------------------------------------------------------------------- |
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9 |
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10 This is a description, based on reverse engineering, of the flash file system |
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11 (FFS) implemented in Pirelli's original firmware for the DP-L10 GSM/WiFi dual |
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12 mode mobile phone, and in the Closedmoko GTA0x modem firmware. Not knowing the |
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13 "proper" name for this FFS, and needing _some_ identifier to refer to it, I |
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14 have named it Mokopir-FFS, from "Moko" and "Pirelli" - sometimes abbreviated |
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15 further to MPFFS. |
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16 |
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17 (I have previously called the FFS in question MysteryFFS; but now that I've |
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18 successfully reverse-engineered it, it isn't as much of a mystery any more :-) |
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19 |
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20 At a high functional level, Mokopir-FFS presents the following features: |
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21 |
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22 * Has a directory tree structure like UNIX file systems; |
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23 |
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24 * The file system API that must be implemented inside the proprietary firmware |
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25 appears to use UNIX-style pathnames; doing strings on firmware images reveals |
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26 pathname strings like these: |
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27 |
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28 /var/dbg/dar |
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29 /gsm/l3/rr_white_list |
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30 /gsm/l3/rr_medium_rxlev_thr |
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31 /gsm/l3/rr_upper_rxlev_thr |
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32 /gsm/l3/shield |
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33 |
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34 Parsing the corresponding FFS image with tools included in the present |
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35 package has confirmed that the directory structure implied by these pathnames |
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36 does indeed exist in the FFS. |
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37 |
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38 * Absolutely no DOS-ish semantics seen anywhere: no 8.3 filenames and no |
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39 colon-separated device names (seen in the TSM30 file system source, for |
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40 example) are visible in the Closedmoko/Pirelli FFS. |
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41 |
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42 * File contents are stored uncompressed, but not necessarily contiguous: one |
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43 could probably store a file in FFS which is bigger than the flash sector |
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44 size, it which case it can never be contiguous in a writable FFS (see below), |
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45 and the firmware implementation seems to limit chunk sizes to a fairly small |
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46 number: on the Pirelli phones all largish files are divided into chunks of |
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47 8 KiB each, and on my GTA02 the largest observed chunk size is only 2 KiB. |
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48 |
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49 The smaller files, like the IMEI and the firmware ID strings in my GTA02 FFS, |
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50 are contiguous. |
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51 |
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52 * The FFS structure is such that the length of "user" payload data stored in |
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53 each chunk (and consequently, in each file) can be known exactly in bytes, |
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54 with the files/chunks able to contain arbitrary binary data. (This property |
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55 may seem obvious or trivial, as all familiar UNIX and DOS file systems have |
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56 it, but contrast with RT-11 for example.) |
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57 |
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58 * The flash file system is a writable one: the running firmware can create, |
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59 delete and overwrite files (and possibly directories too) in the live FFS; |
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60 thus the FFS design is such that allows these operations to be performed |
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61 within the physical constraints of NOR flash write operations. |
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62 |
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63 I have reverse-engineered this Mokopir-FFS on a read-only level. What it means |
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64 is that I, or anyone else who can read this document and the accompanying |
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65 source for the listing/extraction utilities, can take a Mokopir-FFS image read |
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66 out of a device and see/extract its full content: the complete directory tree |
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67 and the exact binary byte content of all files contained therein. |
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68 |
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69 However, the knowledge possessed by the present hacker (and conveyed in this |
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70 document and the accompanying source code) is NOT sufficient for constructing a |
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71 valid Mokopir-FFS image "in vitro" given a tree of directories and files, or |
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72 for making modifications to the file or directory content of an existing image |
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73 and producing a content-modified image that is also valid; valid as in suitable |
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74 for the original proprietary firmware to make its normal read and write |
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75 operations without noticing anything amiss. |
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76 |
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77 Constructing "de novo" Mokopir-FFS images or modifying existing images in such |
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78 a way that they remain 100% valid for all read and write operations of the |
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79 original proprietary firmware would, at the very minimum, require an |
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80 understanding of the meaning of *all* fields of the on-media FFS format. Some |
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81 of these fields are still left as "non-understood" for now though: a read-only |
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82 implementation can get away with simply ignoring them, but a writer/generator |
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83 would have to put *something* in those fields. |
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84 |
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85 As you read the "read-only" description of the Mokopir-FFS on-media format in |
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86 the remainder of this document, it should become fairly obvious which pieces |
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87 are missing before our understanding of this FFS can be elevated to a |
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88 "writable" level. |
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89 |
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90 However, when it comes to writing new code to run on the two Calypso phones in |
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91 question (Closedmoko and Pirelli), it seems, at least to the present hacker, |
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92 that a read-only understanding of Mokopir-FFS should be sufficient: |
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93 |
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94 * In the case of Closedmoko GTA0x modems, the FFS is seen to contain the IMEI |
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95 and the RF calibration data. The format of the former is obvious; the latter |
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96 not so much - but in any case, the information of interest is clearly of a |
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97 read-only nature. It's difficult to tell (or rather, I haven't bothered to |
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98 experiment enough) whether the Closedmoko firmware does any writes to FFS or |
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99 if the FFS is treated as read-only outside of the production line environment, |
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100 but in any case, it seems to me that for any 3rd party replacement firmware, |
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101 the best strategy would be to treat the FFS as a read-only source of IMEI and |
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102 RF calibration data, and nothing more. |
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103 |
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104 * In the case of Pirelli phones, the FFS is used to store user data: sent and |
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105 received SMS (and MMS/email/whatever), call history, UI settings, pictures |
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106 taken with the camera, and whatever else. It also stores a ton of files |
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107 which I can only presume were meant to be immutable except at the time of |
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108 firmware updates: graphics for the UI, ringtones, i18n UI strings, and even |
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109 "helper" firmware images for the WiFi and VoIP processors. However, no IMEI |
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110 or RF calibration data are anywhere to be found in the FFS - instead this |
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111 information appears to be stored in the "factory block" at the end of the |
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112 flash (in its own sector) outside of the FFS. |
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113 |
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114 Being able to parse FFS images extracted out of Pirelli phones "in vitro" |
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115 allows us to steal some of these helper files (UI artwork, ringtones, |
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116 WiFi/VoIP helpers), and some of these might even come useful to firmware |
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117 replacement projects, but it seems to me that a replacement firmware would |
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118 be better off using its own FFS design for storing user data, and as to |
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119 retrieving the original IMEI and RF calibration data, the original FFS isn't |
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120 of any use for that anyway. |
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121 |
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122 ======================= |
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123 Moko/Pirelli FFS format |
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124 ======================= |
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125 |
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126 OK, now that I'm done with the introduction, we can get to the actual |
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127 Mokopir-FFS format. |
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128 |
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129 * On the GTA0x modem (or at least on my GTA02; my sample size is 1) the FFS |
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130 occupies 7 flash sectors of 64 KiB each at offsets 0x380000 through 0x3E0000, |
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131 inclusive. |
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132 |
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133 (The 4 MiB NOR flash chip used by Closedmoko has an independent R/W bank |
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134 division between the first 3 MiB and the last 1 MiB. The first 3 MiB are used |
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135 to hold the field-flashable closed firmware images distributed as *.m0 files; |
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136 the independent last megabyte holds the FFS, and thus the FW could be |
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137 implemented to do FFS writes while running from flash in the main bank. |
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138 Less than half of that last megabyte appears to be used for the FFS though; |
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139 the rest appears to be unused - blank flash observed.) |
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140 |
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141 * On the Pirelli the FFS occupies 18 sectors of 256 KiB each at offsets 0 |
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142 through 0x440000 (inclusive) of the 2nd flash chip select, the one wired to |
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143 nCS3 on the Calypso. |
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144 |
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145 Each flash sector allocated to FFS begins with the following signature: |
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146 |
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147 00000000: 46 66 73 23 10 02 xx yy zz FF FF FF FF FF FF FF Ffs#............ |
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148 |
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149 The bytes shown as xx and yy above serve a non-understood purpose; as a guess, |
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150 they may hold some info for the flash wear leveling algorithm: in a "virgin" |
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151 FFS image like that found in my GTA02 (which never had a SIM card in it and |
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152 never made or received a call) or read out of a "virgin" Pirelli phone that |
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153 hasn't seen any active use yet, both of these bytes are FFs, but when I look at |
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154 FFS images read out of the Pirelli which I currently use as my everyday-use |
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155 cellphone, I see other values in sectors which must have been erased and |
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156 rewritten. A read-only implementation can ignore these bytes, as mine does. |
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157 |
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158 The byte shown as zz is more important though, even to a read-only |
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159 implementation. The 3 values I've encountered in this byte so far are AB, BD |
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160 and BF. Per my current understanding, in a "healthy" FFS exactly one sector |
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161 will have AB in its header, exactly one will have BF, and the rest will have |
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162 BD. The meanings are (or appear to be): |
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163 |
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164 AB: the sector holds a vital data structure which I have called the active |
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165 index block; |
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166 BD: the sector holds regular data; |
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167 BF: the sector is blank except for the header, can be turned into a new AB or |
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168 BD. |
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169 |
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170 (Note that a flash program operation, which can turn 1s into 0s but not the |
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171 other way around, can turn BF into either AB or BD - but neither AB nor BD can |
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172 be turned into any other valid value.) |
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173 |
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174 In a "virgin" FFS image (as explained above) the first FFS sector is AB, the |
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175 last one is BF, and the ones in between are BDs. |
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176 |
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177 An FFS read operation (a search for a given pathname, or a listing of all |
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178 present directories and files) needs to start with locating the active index |
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179 block - the FFS sector with AB in the header. Following this header, which is |
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180 treated as being 16 bytes long (almost everything in Mokopir-FFS is aligned on |
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181 16-byte boundaries), the active index block contains a linear array of 16-byte |
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182 records, each record describing an FFS object: directory, file or file |
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183 continuation chunk. |
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184 |
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185 Here is my current understanding of the 16-byte index block record structure: |
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186 |
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187 2 bytes: Length of the described chunk in bytes |
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188 1 byte: Purpose/meaning not understood, ignored by my current code |
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189 1 byte: Object type |
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190 2 bytes: Descendant pointer |
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191 2 bytes: Sibling pointer |
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192 4 bytes: Data pointer |
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193 4 bytes: Purpose/meaning not understood, ignored by my current code |
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194 |
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195 (On the Calypso phones of interest, all multibyte fields are in the native |
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196 little-endian byte order of the ARM7TDMI processor.) |
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197 |
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198 The active index block gets filled with these records as objects are created; |
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199 the first record goes right after the 'Ffs#'...AB header (padded to 16 bytes); |
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200 the last record (at any given moment) is followed by blank flash for the |
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201 remainder of the sector. Records thus appear in the order in which they are |
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202 created, which bears no direct relation to the directory tree structure. |
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203 |
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204 The objects, each described by a record in the index block, are organized into |
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205 a tree structure by the descendant and sibling pointers, plus the object type |
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206 indicator byte. Let's start with the latter; the following objtype byte values |
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207 have been observed: |
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208 |
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209 00: deleted object - a read-only implementation should ignore everything except |
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210 the descendant and sibling pointers. (A write-capable implementation would |
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211 need more care - it would need a way of reclaiming dirty flash space taken |
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212 up by deleted/overwritten files.) |
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213 |
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214 E1: a special file - see the description of the /.journal file further down |
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215 F1: a regular file (head chunk thereof) |
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216 F2: a directory |
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217 F4: file continuation chunk (explained below) |
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218 |
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219 Each record in the index block has an associated chunk in one of the data |
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220 sectors; the index record contains fields giving the address and length of this |
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221 chunk. The length of a chunk is always a nonzero multiple of 16 bytes, and is |
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222 stored (as a number in bytes) in the first 16-bit field of the 16-byte index |
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223 entry. The address of each chunk is given by the data pointer field of the |
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224 index record, and it is reckoned in 16-byte units (thereby 16-byte alignment is |
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225 required) from the beginning of the FFS sector group in the flash address space. |
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226 |
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227 For objects of type F1 and F2 (regular files and directories) the just-described |
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228 chunk begins with the name of the file or subdirectory as a NUL-terminated ASCII |
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229 string. This name is just for the current level of the directory tree, just |
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230 like in UNIX directories, thus one will have chunk names like gsm, l3, eplmn |
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231 etc, rather than /gsm/l3/eplmn. One practical effect is that one can't readily |
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232 see pathnames or any of the directory structure by looking at an FFS image as a |
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233 raw hex dump; the structure is only revealed when one uses a parsing program |
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234 like those which accompany this document. |
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235 |
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236 In the case of directories, the "chunk" part of the object contains only the |
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237 name of the directory itself, padded with FFs to a 16-byte boundary. For |
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238 example, an FFS directory named /gsm would be represented by an object |
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239 consisting of two flash writes: a 16-byte entry in the active index block, with |
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240 the object type byte set to F2, and a corresponding 16-byte chunk in one of the |
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241 data sectors, with the 16 bytes containing "gsm", a terminating NUL byte, and |
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242 12 FF bytes to pad up to 16. In the case of files, this name may be followed |
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243 by the first chunk of file data content, as explained further down. |
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244 |
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245 In order to parse the FFS directory tree (whether the objective is to dump the |
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246 whole thing recursively or to find a specific file given a pathname), one needs |
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247 to first (well, after finding the active AB block) find the root directory node. |
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248 The root directory object is similar to other directory objects: it has a type |
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249 of F2, and an associated chunk of 16 bytes in one of the data sectors. The |
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250 latter contains the name of the root node: on the Pirelli it is "/", whereas on |
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251 my GTA02 it is "/ffs-root". |
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252 |
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253 The astute reader should notice that it really makes no sense to store a name |
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254 for the root node, and indeed, this name plays no part in the traversal of the |
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255 directory tree given an absolute pathname. But instead this name, or rather |
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256 its first character, appears to be used for the purpose of locating the root |
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257 node itself. At first I had assumed that the index record for the root node is |
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258 always the first record in the active index block right after the signature |
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259 header - that is how it is in "virgin" FFS images, and also in some quite non- |
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260 virgin ones I have pulled from my daily-use Pirelli. Naturally my first version |
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261 of the Mokopir-FFS (then called MysteryFFS) extraction utility expected the root |
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262 node to always be at index #1. But then I got some additional Pirelli phones, |
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263 and discovered that in certain cases, index record #1 is a deleted object (the |
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264 original root node which has been deleted), and the new active root node is |
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265 somewhere in the middle of the index! |
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266 |
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267 Thus it appears that in order to find the active root node, one needs to scan |
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268 the active index block linearly from the beginning (disregarding the tree |
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269 structure pointers in this initial pass), looking for a non-deleted object of |
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270 type F2 (a directory) whose corresponding name chunk sports a name beginning |
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271 with the '/' character. (Anyone who's been raised in UNIX will immediately |
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272 know that the path separator character '/' is the only character other than NUL |
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273 that's absolutely forbidden in the individual filenames - so this special |
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274 "root node name" is the only case of a '/' character appearing in what would |
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275 otherwise be a regular filename.) |
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276 |
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277 [What causes the root node to be somewhere other than at index #1? I assume it |
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278 has to do with the dirty space reclamation / data movement algorithm. In a |
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279 "virgin" FFS image the very first sector is the active index block, and the |
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280 following sector is the first to hold chunks, beginning with the name chunk of |
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281 the root node. Now what happens if all data in that sector aside from the |
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282 root node name and some other mostly-static directory names becomes dirty, |
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283 i.e., belonging to deleted or overwritten files? How would that flash space |
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284 get reclaimed? I assume that the FFS firmware algorithm moves all still-active |
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285 chunks to a new flash sector, invalidating the old copies - turning the latter |
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286 into deleted objects. The root node will be among them. Then at some point |
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287 the active index block is going to fill up too, and will need to be rewritten |
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288 into a new sector - at which point the previously-deleted index entries are |
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289 omitted and the root node becomes #1 again...] |
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290 |
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291 Tree structure |
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292 |
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293 Once the root node has been found, the descendant and sibling pointers are used |
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294 to traverse the tree structure. For each directory object, including the root |
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295 node, the descendant pointer points to the first child object of this directory: |
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296 the first file or subdirectory contained therein. (Descendant and sibling |
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297 pointers take the form of index numbers in the active index block. A "nil" |
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298 pointer is indicated by all 1s (FFFF) - the usual all-0s NULL pointer convention |
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299 couldn't be used because it's flash, where the blank state is all 1s.) If the |
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300 descendant pointer of a directory object is nil, that means an empty directory. |
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301 The sibling pointer of each file or directory points to its next sibling, i.e., |
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302 the next member of the same parent directory. The sibling pointer of the root |
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303 node is nil. |
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304 |
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305 Data content of files |
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306 |
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307 Objects of type F1 are the head chunks of files. Each file has a head chunk, |
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308 and may or may not have continuation chunks. More precisely, the head chunk |
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309 may contain only the name (or viewed alternatively, 0 bytes of data), or it may |
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310 contain a nonzero number of payload bytes; orthogonally to this variability, |
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311 there may or may not be continuation chunk(s) present. |
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312 |
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313 Continuation chunks |
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314 |
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315 The descendant pointer of each file head object (the object of type F1, the one |
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316 reached by traversing the directory tree) indicates whether or not there are |
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317 any continuation chunks present. If this descendant pointer is nil, there are |
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318 no continuation chunks; otherwise it points to the first continuation chunk |
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319 object. File continuation objects have type F4, don't have any siblings (the |
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320 sibling pointer is nil - but see below regarding relocated chunks), and the |
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321 descendant pointer of each continuation object points to the next continuation |
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322 object, if there is one - nil otherwise. |
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323 |
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324 Payload data delineation |
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325 |
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326 Each chunk, whether head or continuation, always has a length that is a nonzero |
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327 multiple of 16 bytes. The length of the chunk here means the amount of flash |
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328 space it occupies in its data sector - which is NOT equal to the payload data |
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329 length. |
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330 |
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331 The head chunk of each file begins with the filename, terminated by a NUL byte. |
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332 If there are any payload data bytes present in this head chunk (I'll explain |
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333 momentarily how you would tell), the byte immediately after the NUL that |
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334 terminates the filename is the first byte of the payload. In the case of a |
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335 continuation chunk, there is no filename and the first byte of the chunk is the |
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336 first byte of that chunk's portion of the user data payload. |
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337 |
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338 Each data-containing chunk (head or continuation) has the following termination |
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339 after the last byte of that chunk's payload data: one byte of 00, followed by |
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340 however many bytes are needed ([0,15] range) of FFs to pad to a 16-byte |
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341 boundary. A file head chunk that has no payload data has the same format as a |
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342 directory name chunk: filename followed by its terminating NUL followed by |
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343 [0,15] bytes of FFs to pad to the next 16-byte boundary. |
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344 |
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345 When working with a head chunk, find the beginning of possible payload data (1 |
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346 byte after the filename terminating NUL) and find the end per the standard |
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347 termination logic: scanning from the end of the chunk, skip FFs until 00 is |
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348 found (encountering anything else is an error). If the head chunk has no data, |
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349 the effective data length (end_pointer - start_pointer) will be 0 or -1. (The |
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350 latter possibility is the most likely, as there will normally be a "shared" 00 |
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351 byte, serving as both the filename terminator and the 00 before the padding |
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352 FF bytes.) |
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353 |
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354 Relocated chunks |
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355 |
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356 Let's go back to the scenario in which a particular data sector is full (no more |
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357 usable free space left) and contains a mixture of active and dirty (deleted or |
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358 invalidated) data. How does the dirty flash space get reclaimed, so that the |
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359 amount of available space (blank flash ready to hold new data) becomes equal to |
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360 the total FFS size minus the total size of active files and overhead? It can |
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361 only be done by relocating the still-active objects from the full sector to a |
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362 new one, invalidating the old copies, and once the old sector consists of |
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363 nothing but invalidated data, subjecting it to flash erasure. |
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364 |
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365 So how do the active FFS objects get relocated from a "condemned" sector to a |
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366 new one? If the object is a directory, a new index entry is created, pointing |
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367 to the newly relocated name chunk, but it is then made to fit into the old tree |
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368 structure without disrupting the latter: the new index entry is added at the |
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369 tail of the sibling-chain of the parent directory's descendants, the old index |
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370 entry for the same directory is invalidated (as if the directory were rmdir'ed), |
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371 and the descendant pointer of the newly written index entry is set to a copy of |
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372 the descendant pointer from the old index entry for the same directory. The |
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373 same approach is used when the head chunk of a file needs to be relocated; in |
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374 both cases a read-only FFS implementation doesn't need to do anything special to |
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375 support reading file and directory objects that have been relocated in this |
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376 manner. |
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377 |
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378 However, if the relocated object is a file continuation chunk, then the manner |
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379 in which such objects get relocated does affect file reading code. What if a |
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380 chunk in the middle of a chain linked by "descend" pointers needs to be moved? |
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381 What happens in this case is that the old copy of the chunk gets invalidated |
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382 (the object type byte turned to 00) like in the other object relocating cases, |
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383 and the sibling pointer of that old index entry (which was originally FFFF as |
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384 continuation objects have no siblings) is set to point to the new index entry |
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385 for the same chunk. The "descend" pointer in the new index entry is a copy of |
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386 that pointer from the old index entry. |
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387 |
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388 The manner of chunk relocation just described has been observed in the FFS |
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389 images read out of my most recent batch of Pirelli phones - the same ones in |
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390 which the root directory object is not at index #1. Thinking about it as I |
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391 write this, I've realized that the way in which continuation objects get |
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392 relocated is exactly the same as for other object types - thus the compaction |
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393 code in the firmware doesn't need to examine what object type it is moving. |
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394 However, the case of continuation chunk relocation deserves special attention |
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395 because it affects a read-only implementation like ours - the utilities whose |
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396 source accompanies this document used to fail on these FFS images until I |
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397 implemented the following additional handling: |
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398 |
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399 When following the chunk chain of a file, normally the only object type that's |
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400 expected is F4 - any other object type is an error. However, as a result of |
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401 chunk relocation, one can also encounter deleted objects, i.e., type == 00. |
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402 If such a deleted object is encountered, follow its sibling pointer, which must |
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403 be non-nil. |
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404 |
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405 Journal file |
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406 |
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407 Every Mokopir-FFS image I've seen so far contains a special file named |
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408 /.journal; this file is special in the following ways: |
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409 |
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410 * The object type byte is E1 instead of F1; |
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411 * Unlike regular files, this special file is internally-writable. |
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412 |
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413 What I mean by the above is that regular files are mostly immutable: once a |
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414 file has been created with some data content in the head chunk, it can only be |
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415 either appended to (one or more continuation chunks added), or overwritten by |
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416 creating a new file with the same name at the same level in the tree hierarchy |
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417 and invalidating the old one. But the special /.journal file is different: I |
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418 have never observed it to consist of more than the head chunk, and this head |
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419 chunk is pre-allocated with some largish and apparently fixed length (4 KiB on |
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420 my GTA02, 16 KiB on the Pirelli). This pre-allocated chunk contains what look |
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421 like 16-byte records at the beginning (on the first 4-byte boundary after the |
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422 NUL terminating the ".journal" name), followed by blank flash for the remainder |
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423 of the pre-allocated chunk - so it surely looks like new flash writes happen |
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424 within this chunk. |
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425 |
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426 I do not currently know the purpose of this /.journal file or the meaning of the |
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427 records it seems to contain. This understanding would surely be needed if one |
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428 wanted to create FFS images from scratch or to implement FFS write operations, |
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429 but I reason that a read-only implementation can get away with simply ignoring |
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430 this file. I reason that this file can't be necessary in order to parse an FFS |
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431 image for reading because one needs to parse the tree structure first in order |
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432 to locate this journal file itself. |
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433 |
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434 ------------------------------------------------------------------------------- |
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435 |
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436 That's all I can think of right now. If anything is unclear, see the |
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437 accompanying source code for the listing/extraction utilities: with the general |
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438 explanation given by this document, it should be clear what my code does and |
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439 why. And if a given piece of knowledge is found neither in this document nor |
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440 in my source code, then I don't know it myself either, and my read-only |
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441 Mokopir-FFS implementation makes do without it. |
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442 |
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443 All knowledge contained herein has been recovered by reverse engineering. |
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444 Believe it or not, I have figured it out by staring at the hex dump of FFS |
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445 sectors, reasoning about how one could possibly implement an FFS given the |
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446 requirement of dynamic writability and the physical constraints of flash memory, |
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447 and writing listing/extraction test code iteratively until I got something that |
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448 appears to correctly parse all FFS images available to me - the result is the |
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449 code in this package. |
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450 |
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451 I never got as far as attempting to locate the FFS implementation routines |
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452 within the proprietary firmware binary code images, and I haven't found an |
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453 implementation of this particular FFS in any of the leaked sources yet either. |
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454 The TSM30 code doesn't seem to be of any use as its FFS appears to be totally |
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455 different. As to the more recently found LoCosto code leak, I found that one a |
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456 few days *after* I got the Moko/Pirelli "MysteryFFS" reverse-engineered on my |
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457 own, and when I did look at the FFS in the LoCosto code later, I saw what seems |
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458 to be a different FFS as well. |
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459 |
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460 Michael Spacefalcon |
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461 SE 52 Mes 16 |