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annotate doc/TIFFS-Overview @ 445:9eeeef3ff7db

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os_sem_fl.c: os_QuerySemaphore() done
author Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
date Mon, 23 Jun 2014 01:19:50 +0000
parents 14618bd924ec
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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1 All TI GSM firmwares known to this author (FreeCalypso developer Space Falcon)
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2 implement some kind of flash file system, or FFS. Several different FFS code
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3 implementations, and correspondingly several different on-flash data formats,
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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4 have been used throughout the history of TI's involvement in the wireless
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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5 terminal business. The FFS incarnation of primary interest to the FreeCalypso
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6 project is the one invented by Mads Meisner-Jensen at TI in the early 2000s
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7 (at least according to the comments in the sources available to us), and it is
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8 relevant to us in the following ways:
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9
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10 * When targeting the GSM modem in Openmoko's GTA01/02 smartphones, we need to
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11 work with the original FFS from the factory (call it MokoFFS), the same FFS
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12 as used by the mokoN firmwares: this FFS contains the IMEI and the RF
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13 calibration values from the factory, which we most certainly don't want to go
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14 without.
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15
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16 * The Leonardo firmware semi-src which we are using as the reference for
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17 building our own full source, multi-target GSM fw contains a turnkey-working
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18 implementation of this very FFS, using the on-flash format in question and
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19 providing run-time APIs expected by the rest of the GSM fw suite. Following
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20 the principle of ``if it ain't broke, don't fix it'', we can use this FFS not
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21 only on the gtamodem target, but also on other targets, including those where
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22 we would be starting from a blank state and thus have the freedom to use
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23 whatever FFS we like.
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24
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25 * The original proprietary fw on the Pirelli DP-L10 phone also happens to use
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26 an FFS in the same format. Pirelli's FFS does *not* contain the IMEI or any
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27 of the RF calibration values though, and trying to reuse it directly for our
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28 own FC GSM fw seems to be more trouble than benefit - so we'll probably have
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29 our fw start with a blank TIFFS instead - but there is still insight to be
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30 gained from in-vitro examination of captured Pirelli FFS images.
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31
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32 Naming
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33 ======
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34
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35 I have previously referred to the FFS format in question as Mokopir-FFS or
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36 MPFFS, from "Moko" and "Pirelli". I was originally hesitant to call it TIFFS,
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37 as lacking the source code, I had no way of knowing whether the FFS format and
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38 implementation were of TI's own invention, or something that TI licensed as a
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39 black box from one of their many proprietary software partners. (I was unable
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40 to identify it as any well-known, industry-standard FFS format, but absence of
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41 evidence is not evidence of absence.) But now that we have TI's original source
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42 code which implements this FFS (first the MV100-0.1.rar source, then the full
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43 Leonardo one), complete with comments and a HISTORY file, we know that our FFS
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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44 was invented and implemented by someone named Mads Meisner-Jensen at TI - I'm
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45 guessing in the SSA group in Nice, France.
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46
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47 I am now making a naming transition from MPFFS to TIFFS: there is really no
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48 link between this FFS format and the Openmoko+Pirelli duo, other than the
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49 happenstance of me having first encountered this FFS on these two GSM device
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50 brands, and the name TIFFS is more neutrally-descriptive.
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51
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52 What it is
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53 ==========
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54
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55 In a rare departure from TI's norm (most of TI's GSM firmware and associated
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56 development tools suffer from heavy Windows poisoning), what I call TIFFS is
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57 very Unixy. It is a file system with a hierarchical directory tree structure
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58 and with Unixy forward-slash-separated, case-sensitive pathnames; the semantics
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59 of "what is a file" and "what is a directory" are exactly the same as in UNIX;
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60 and TIFFS even supports symlinks, although that support is a little under-
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61 developed, and apparently no FFS symlinks were ever used in any production GSM
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62 device. Thus the FFS implemented in TI-based GSM devices (modems and
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63 "dumbphones") is really no different from, for example, JFFS2 in embedded Linux
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64 systems.
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65
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66 (The only traditional UNIX file system features which are missing in TIFFS are
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67 the creation/modification/access timestamps and the ownership/permission
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68 fields.)
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69
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70 The FFS in a GSM device typically stores two kinds of content:
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71
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72 * Factory data: IMEI, RF calibration values, device make/model/revision
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73 ID strings etc. These files are expected to be programmed on the factory
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74 production line and not changed afterward.
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75
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76 * Dynamic data written into the FFS in normal device operation: when you use a
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77 "dumbphone" running TI-based firmware, every time you store something "on the
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78 phone" or in "non-volatile memory", that item is actually stored in the FFS.
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79 (Where else, if you think of it?) That includes contacts and received SMS
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80 stored "on the phone" instead of the SIM, any selections you make in the
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81 settings/preferences menus which persist across reboots (power cycles), call
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82 history etc.
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83
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84 It needs to be noted that the "dynamic data" aspect of FFS usage applies not
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85 only to complete phones, but also to modems like the one used in the GTA01/02.
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86 One would naively think that non-volatile storage of data in flash outside of
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87 factory programming would be needed only in a device with its own UI, and that
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88 a modem subservient to external AT commands would be completely stateless
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89 across reboot/power cycles; but that is not the case in actuality. TI's GSM
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90 firmwares, including the Openmoko ones (the "standard" mokoN), are designed to
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91 always "mount" their FFS with read/write access; TI's FFS implementation in the
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92 firmware has no concept of a "read-only mount".
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93
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94 I am still investigating just what kinds of data are routinely written into the
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95 non-volatile FFS by the firmware in normal operation on devices like the GTA0x
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96 modem, but there most definitely are some.
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97
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98 There is no hard separation between "static" and "dynamic" data in the file
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99 system structure; TIFFS is thus akin to an embedded Linux system with just a
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100 single root file system containing both "static" files like userland binaries
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101 and "dynamic" ones like configuration files under /etc which the user is
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102 expected to edit with vi after logging into the box, or log and similar files
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103 created by the system itself under /var, for example.
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104
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105 Where it lives
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106 ==============
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107
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108 The type of flash memory used in Calypso GSM modems and "dumbphones" is called
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109 NOR flash. This NOR flash memory is physically divided (by the design of the
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110 flash chip itself) into units called "sectors" or more descriptively, erase
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111 blocks. The typical NOR flash sector size (in Calypso GSM devices) ranges from
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112 64 KiB in the GTA02 modem's NOR flash (4 MiB total) to 256 KiB in the
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113 S71PL129NC0 flash+RAM chip used in the Pirelli DP-L10 (16 MiB of flash total).
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114 The key physical property is that any bit may be changed from a '1' to a '0' at
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115 any time, in any combination, but resetting of '0' bits back to ones can be
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116 done only on the granularity of these largish sectors, in an operation called
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117 "sector erase".
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118
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119 The location of TIFFS within the flash memory of a given GSM device is defined
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120 by the firmware design of that device, but is always some integral number of
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121 contiguous flash sectors. Some examples:
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122
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123 * On the GTA01/02 GSM modem, FFS occupies 7 sectors of 64 KiB each, starting at
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124 flash offset 0x380000.
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125
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126 * On the Pirelli DP-L10, the FFS used by the original proprietary fw occupies
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127 18 sectors of 256 KiB each (for 4.5 MiB in total), starting at the beginning
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128 of the 2nd flash chip select (0x02000000 in the ARM7 address space).
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diff changeset
129
430
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130 * On Motorola/Compal C139/140 phones, the FFS used by the original proprietary
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diff changeset
131 fw occupies 5 sectors of 64 KiB each (320 KiB in total), starting at 0x370000.
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132 C11x/123 use smaller FFS configurations, whereas C155/156 seem to have
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133 switched to some other FFS format, different from our familiar TIFFS.
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diff changeset
134
227
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135 * The smallest real FFS configuration called for by the table in dev.c in TI's
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diff changeset
136 original Leonardo fw source is 3 sectors of 64 KiB each; the same table also
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137 sports a 4 KiB x 4 configuration for RAM-based testing (emulation of FFS in
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138 RAM without real flash).
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139
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140 * The largest FFS configuration that has been envisioned by the original
1852900ce9ea doc/TIFFS write-up
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diff changeset
141 designers seems to be somewhere around 128 sectors.
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diff changeset
142
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143 Each flash sector used for TIFFS begins with this 6-byte signature:
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144
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145 46 66 73 23 10 02
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diff changeset
146
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diff changeset
147 The first 4 bytes are 'Ffs#' in ASCII, and the following two bytes are the
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148 format version number of 0x0210 in little-endian byte order. The following two
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diff changeset
149 bytes give a count of how many times that sector has been erased and rewritten
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diff changeset
150 (FF FF in "fresh" or "virgin" FFS images), and the following byte indicates
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diff changeset
151 that block's role and status in the FFS life cycle.
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152
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153 How it works
1852900ce9ea doc/TIFFS write-up
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diff changeset
154 ============
1852900ce9ea doc/TIFFS write-up
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155
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diff changeset
156 Just like JFFS2 and other high-quality flash file systems, TIFFS is designed to
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157 recover gracefully from any possible power failure or crash: one can yank the
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diff changeset
158 battery from the GSM device (or induce a firmware crash) at the most mis-
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diff changeset
159 opportune moment in the middle of an FFS write operation, and the FFS is
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diff changeset
160 expected to recover on the next boot cycle. I won't be able to document here
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diff changeset
161 all gory details of exactly how this goal is achieved, partly because I haven't
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diff changeset
162 studied the code to the requisite level of depth myself yet, but all of the
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diff changeset
163 responsible code lives under gsm-fw/services/ffs in this freecalypso-sw source
1852900ce9ea doc/TIFFS write-up
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diff changeset
164 tree; feel free to study it.
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diff changeset
165
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diff changeset
166 In its "normal" or "clean" state (i.e., when not in the middle of a write
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167 operation or recovery from an ungracefully interrupted one), a TIFFS instance
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168 consists of the following 3 types of blocks:
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169
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170 * One block containing inode records, indicated by AB in its type/flags/status
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diff changeset
171 byte in the block header;
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172 * N-2 blocks (where N is the total number of flash sectors allocated for the
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173 FFS) containing (or waiting to be filled with) data chunks - indicated by BD
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174 in the type/flags/status byte;
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175 * One "free" block, indicated by BF - destined to become a new AB or a new BD
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diff changeset
176 at some point.
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diff changeset
177
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diff changeset
178 Each object written into the FFS (file, directory or symlink) consists of a
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diff changeset
179 16-byte inode record written into the AB block and a data chunk written into
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diff changeset
180 one of the BD blocks. The data chunk includes the name of the object, hence
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diff changeset
181 one is required even for directories. Data chunks are contiguous, uncompressed,
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diff changeset
182 and subject to an upper size limit of 2048 or 8192 bytes, depending on the FFS
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
183 configuration. Files larger than this limit are stored in a "segmented" form,
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diff changeset
184 giving rise to a 4th inode or object type (after file, directory and symlink):
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diff changeset
185 segment. Each segment of a segmented file consists of not only a data chunk,
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diff changeset
186 but also an inode record for the segment, which gives the location of the data
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diff changeset
187 chunk and ties the segment object into the overall FFS structure, making it
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diff changeset
188 accessible.
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diff changeset
189
1852900ce9ea doc/TIFFS write-up
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diff changeset
190 Because aside from complete sector erasure, flash memory bits can only
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diff changeset
191 transition from '1' to '0' but not the other way around, overwriting an existing
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parents: 224
diff changeset
192 file with some new content (an operation which any reasonable file system must
1852900ce9ea doc/TIFFS write-up
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diff changeset
193 implement in some way) cannot be done in place. Instead like most flash file
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diff changeset
194 systems, TIFFS implements this common operation by writing the new version of
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diff changeset
195 the file to a new location (previously blank flash) and then invalidating the
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diff changeset
196 old version - and doing all that while keeping in mind the possibility of an
1852900ce9ea doc/TIFFS write-up
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diff changeset
197 ungraceful crash or powerdown at any moment, and the requirement of recovering
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diff changeset
198 gracefully from any such event.
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diff changeset
199
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diff changeset
200 Of course as an FFS receives more write activity, even if one keeps overwriting
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diff changeset
201 some existing files with new content of the same size, without adding to the
1852900ce9ea doc/TIFFS write-up
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diff changeset
202 visible total content size (think du(1) command), eventually all remaining blank
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parents: 224
diff changeset
203 flash space will fill up. At that point (or at some earlier point, depending
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parents: 224
diff changeset
204 on the FFS design and/or configuration) the FFS has to invoke a compaction or
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parents: 224
diff changeset
205 reclamation or garbage collection procedure: any "mixed" blocks containing both
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
206 valid and stale data are transitioned into a "stale-only" state by having the
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
207 active data moved to a new block, and then the "all stale" blocks are subjected
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parents: 224
diff changeset
208 to sector erasure, becoming new blank sectors. The logic responsible for these
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
209 operations once again needs to be resilient to the possibility of a crash or
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
210 powerdown occurring at the most mis-opportune moment, and it also needs to
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diff changeset
211 implement flash wear leveling: there is a physical limit to how many times a
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diff changeset
212 given flash sector can be erased and rewritten before it goes bad.
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diff changeset
213
1852900ce9ea doc/TIFFS write-up
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diff changeset
214 All of the above are common and well-known principles, successfully implemented
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
215 in well-known flash file systems such as JFFS2 in Linux. TIFFS is absolutely
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parents: 224
diff changeset
216 no different in this regard; for the implementation details, read the source
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parents: 224
diff changeset
217 code.
1852900ce9ea doc/TIFFS write-up
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diff changeset
218
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diff changeset
219 How this FFS comes into being
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diff changeset
220 =============================
1852900ce9ea doc/TIFFS write-up
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diff changeset
221
1852900ce9ea doc/TIFFS write-up
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diff changeset
222 (This section is only relevant to you if you plan on physically producing your
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
223 own GSM phones or modems on your own factory production line, like this author
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
224 fancies doing in the not-too-distant future, or if you simply enjoy knowing
1852900ce9ea doc/TIFFS write-up
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 224
diff changeset
225 how it is done.)
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
226
1852900ce9ea doc/TIFFS write-up
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diff changeset
227 To my knowledge, TI never used or produced a tool akin to mkfs.jffs2 in the
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
228 embedded Linux world, which would produce a TIFFS image complete with some
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
229 initial directory and file content "in vitro". Instead it appears that the FFS
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parents: 224
diff changeset
230 instances found in shipped products such as Openmoko phones have been created
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diff changeset
231 "in vivo" by TI's firmware running on the device itself during the "production
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diff changeset
232 test" phase.
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diff changeset
233
1852900ce9ea doc/TIFFS write-up
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diff changeset
234 The process seems to go like this:
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diff changeset
235
1852900ce9ea doc/TIFFS write-up
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diff changeset
236 * When the printed circuit board is physically populated with components such
1852900ce9ea doc/TIFFS write-up
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diff changeset
237 as the Calypso chip and the flash chip, the latter can be blank - if the
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parents: 224
diff changeset
238 board design has the nIBOOT pin pulled low, enabling the Calypso boot ROM
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
239 (Openmoko and Pirelli both good on this one, but shame on Compal!), there is
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parents: 224
diff changeset
240 no need to preprogram the flash chip with anything prior to populating it on
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parents: 224
diff changeset
241 the board, and the device remains fully unbrickable at all times afterward.
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diff changeset
242
1852900ce9ea doc/TIFFS write-up
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diff changeset
243 * When the assembled board is powered up for the first time, with completely
1852900ce9ea doc/TIFFS write-up
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diff changeset
244 blank flash, the Calypso boot ROM will sit there and patiently wait for a
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diff changeset
245 code download on either of its two UARTs.
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diff changeset
246
1852900ce9ea doc/TIFFS write-up
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diff changeset
247 * Using TI's FLUID (Flash Loader Utility Independent of Device) or FreeCalypso's
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diff changeset
248 fc-loadtool free replacement, the factory production station loads the main
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diff changeset
249 firmware image into the flash. Note, it is just the firmware image at this
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diff changeset
250 step, and the FFS sectors remain blank.
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diff changeset
251
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diff changeset
252 * The board is commanded to reboot (or power-cycled), and the firmware image
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diff changeset
253 boots for the first time.
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diff changeset
254
1852900ce9ea doc/TIFFS write-up
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diff changeset
255 * TI's FFS implementation code in their standard firmware reacts to all blank
1852900ce9ea doc/TIFFS write-up
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diff changeset
256 flash in the FFS sectors as follows: it performs what they call the preformat
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diff changeset
257 operation, writing the TIFFS signature and a BF state byte into every FFS
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parents: 224
diff changeset
258 sector, but the main "format" operation, which sets up the AB/BD block roles,
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259 creates the root inode and makes the FFS ready to accept the creation of its
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260 first directories and files, is not done automatically.
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261
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262 In order to perform the FFS format operation and then fill the new FFS with
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263 whatever directories and files are deemed needed to be present in "fresh"
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diff changeset
264 shipping products, the factory production station connects to the just-booted
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265 firmware running on the target via the RVT/ETM protocol (see the RVTMUX
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266 write-up), and sends "test mode" commands to this running firmware. These
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267 "FFS test mode" (or TMFFS) commands include the format operation, an mkdir
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268 operation to create directories, and a "file write" operation akin to doing
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269 'cat > /dir/whatever/file', creating files in FFS and storing any desired data
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270 in them.
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271
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272 The IMEI is assigned and written into FFS in this process, but it is not the
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diff changeset
273 only data item that will be unique for each individual device made. Much more
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274 important are the RF calibration values: I have yet to learn exactly what is
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275 being (or needs to be) measured, how these measurements are performed (under
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276 what conditions; what external test equipment is needed), and how these measured
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277 and recorded RF calibration values affect GSM device operation, but this TI
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278 presentation gives some clues:
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279
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280 ftp://ftp.ifctf.org/pub/GSM/Calypso/rf_calibration.pdf
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281
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282 All of these calibration values are stored in a bunch of files under the
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283 /gsm/rf subtree, and these files seem to be "owned" by the L1 code. The latter
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284 has RAM data structures which correspond to these files; upon normal boot the
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285 initialization code looks in FFS, and if it finds any of the RF calibration
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286 files, it reads each present file into the corresponding RAM data structure,
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287 overwriting the compiled-in defaults. It appears (slightly uncertain because I
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288 have not yet reintegrated the code in question into our own gsm-fw) that the RF
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289 calibration files in FFS come into being as follows:
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290
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291 * The RF calibration code in L1 (i.e., part of the main GSM fw) performs the
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292 measurements and stores results in its RAM data structures as commanded by
1852900ce9ea doc/TIFFS write-up
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diff changeset
293 the production test station through the "test mode" interface;
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294
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295 * A final test mode command directs the above L1 code to write its RAM data
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296 structures into FFS.
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297
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298 Once I actually learn this RF calibration process properly in connection with
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299 building my own Calypso-based GSM "dumbphone", I'll be able to say exactly what
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diff changeset
300 it would take to recreate these RF calibration values if they are lost. But
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301 until then the only advice I can give is to make a backup copy of your modem
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302 FFS with fc-loadtool, and to save it securely.
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303
430
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304 Compal and Pirelli differences
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305 ==============================
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306
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307 The above description refers to TI's vanilla reference version, and it seems
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308 like Openmoko (FIC) was the only phone/modem manufacturer who followed it
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309 without major deviations. In contrast, both Compal (Mot C1xx) and Foxconn
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310 (Pirelli DP-L10) moved the vital per-unit factory data (IMEI and RF calibration)
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diff changeset
311 out of the FFS into their own ad hoc flash data structures (which are very
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312 difficult to reverse-engineer and make use of, unfortunately), leaving their FFS
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diff changeset
313 only for less critical data.
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314
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315 In Compal's case (at least on the C139 model with which I have extensive
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316 personal experience) the FFS stores only users' personal information and nothing
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317 more. One can turn the phone off, use fc-loadtool to erase the FFS sectors, and
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318 boot the regular fw back up; the fw will automatically do a new FFS format (it
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319 even displays a message on the LCD as it does so) and carry on happily as a
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320 "fresh" or "blank", perfectly functional and usable phone.
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321
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322 In Pirelli's case, booting their official fw with blank FFS sectors will also
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323 result in the FFS being automatically formatted, but their fw expects some
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324 static "asset" files to be present in this FFS: UI graphics and language
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diff changeset
325 strings, ringtones, firmware images for the WiFi and VoIP processors and some
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diff changeset
326 static configuration files, about 3 MiB in total. Thus although the firmware
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327 will auto-format the blank FFS sectors, it won't function normally with all of
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328 these "asset" files missing. Foxconn's original factory production line station
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329 must have uploaded these files to each phone via the TMFFS2 protocol, and our
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diff changeset
330 FreeCalypso suite now features a tool that can replicate this feat: fc-fsio.
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331
227
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332 FreeCalypso support for TIFFS
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diff changeset
333 =============================
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334
250
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335 Aside from implementing and using it in our own gsm-fw, FreeCalypso offers
227
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diff changeset
336 the following support for TIFFS:
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337
250
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338 1. We have a utility for "in vitro" examination of FFS images read out of GSM
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339 devices with fc-loadtool. This tiffs utility (along with mokoffs and pirffs
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340 wrappers) lives in the ffstools top-level directory of the freecalypso-sw
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341 source tree. This TIFFS "in vitro analyzer" utility supplants the earlier
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342 mpffs-* tools, and adds some additional examination functionality. It is
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343 strictly a "read only" tool, however - it is not designed for "in vitro"
430
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344 editing of TIFFS images.
227
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345
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346 2. A number of FC tools may be strung together into a kit for editing the FFS
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347 content of a GSM device, e.g., for changing the IMEI. The following pieces
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348 will be involved:
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349
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350 * What is destined to eventually become our totally free GSM fw (the gsm-fw
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diff changeset
351 source subtree at the top of freecalypso-sw) does not contain any of the
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352 actual GSM protocol stack (or even L1) functionality yet, but it already
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diff changeset
353 contains both the FFS code and those components (ETM and TMFFS[12]) which
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354 are needed for interfacing an external "test mode shell" to this FFS
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355 implementation through the RVTMUX interface. And when our gsm-fw does gain
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diff changeset
356 the actual GSM functionality, the ability to build a minimal FFS+ETM-only
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diff changeset
357 configuration will still be retained.
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diff changeset
358
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diff changeset
359 * The minimal FFS+ETM subset of gsm-fw can be built into a ramImage (runs
1852900ce9ea doc/TIFFS write-up
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diff changeset
360 entirely from RAM via fc-xram, no flashing), and run on a physical device
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diff changeset
361 such as the GTA0x GSM modem via the fc-xram host utility;
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diff changeset
362
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diff changeset
363 * After loading the ramImage, fc-xram will immediately exec our rvinterf host
430
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diff changeset
364 utility (see rvinterf/README);
227
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diff changeset
365
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366 * Once the GSM device is running what is effectively an FFS editing agent out
430
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parents: 250
diff changeset
367 of RAM, accessed via rvinterf over the serial channel, the user can run
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diff changeset
368 fc-tmsh or fc-fsio, and this "test mode shell" provides commands for writing
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diff changeset
369 things to FFS exactly like one would do in the factory production line
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diff changeset
370 environment for which TI taylored their tools.
227
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diff changeset
371
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diff changeset
372 The "in vivo" method of editing the FFS content of a GSM device described above
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diff changeset
373 will probably sound very convoluted, and you may find yourself asking for a way
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diff changeset
374 to do it "in vitro" instead: read the FFS out of flash with fc-loadtool, edit
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
375 that image "in vitro" with some utility on your PC, and then use fc-loadtool
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parents: 224
diff changeset
376 again to program it back into your device. But consider that an "in vitro" FFS
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parents: 224
diff changeset
377 modification would involve erasing and rewriting all sectors of your FFS,
1852900ce9ea doc/TIFFS write-up
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parents: 224
diff changeset
378 whereas an "in vivo" modification of some small file like the IMEI would be
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diff changeset
379 just a short flash write operation without any erasures at all, i.e., kinder
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diff changeset
380 on the flash.
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diff changeset
381
430
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diff changeset
382 In any case, the "in vivo" method is already available now because all of the
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parents: 250
diff changeset
383 components involved therein are also needed for other development uses in the
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parents: 250
diff changeset
384 FreeCalypso project, whereas developing a fully-functional "in vitro"
227
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parents: 224
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385 alternative (one that can create an FFS image "de novo" from a tree of files
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 224
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386 and directories a la mkfs.jffs2, or add new files to an existing TIFFS image
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 224
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387 etc) would be a good amount of extra work which we otherwise don't need - hence
1852900ce9ea doc/TIFFS write-up
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 224
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388 the latter is not very likely to be written any time soon.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 224
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389
1852900ce9ea doc/TIFFS write-up
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 224
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390 However, if the "in vitro" modification you seek is something trivial like
1852900ce9ea doc/TIFFS write-up
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 224
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391 changing the byte content of a file such as /pcm/IMEI or /gsm/com/rfcap without
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 227
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392 changing its length, you can use the existing "in vitro, read-only" tiffs host
3d88461d8284 beginning of TIFFS IVA documentation
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 227
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393 utility to find the exact byte location of the file data within the TIFFS image,
3d88461d8284 beginning of TIFFS IVA documentation
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 227
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394 and then use your favourite hex editor to whack whatever new byte content you
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1852900ce9ea doc/TIFFS write-up
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 224
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395 like at that offset.