annotate doc/Loadtools-performance @ 1008:2b4c3e0f73fc

doc/High-speed-serial: update for current situation
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 10 Dec 2023 23:42:12 +0000
parents 4a1f0bbca58e
children
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1 Memory dump performance
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2 =======================
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4 Here are the expected run times for the flash dump2bin operation of dumping the
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5 entire flash content of a Calypso GSM device with the current version of
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6 fc-loadtool which uses the new binary transfer protocol:
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8 Dump of 4 MiB flash (e.g., Openmoko GTA01/02 or Mot C139/140) at 115200 baud:
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9 6m04s
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11 The same 4 MiB flash dump at 812500 baud: 0m52s
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12
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13 Dump of 8 MiB flash (e.g., Mot C155/156) at 812500 baud: 1m44s
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14
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15 These times are a 2x improvement compared to all previous versions of
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16 fc-loadtool (prior to fc-host-tools-r13) which used a hex-based transfer
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17 protocol.
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19 Because of the architecture of fc-loadtool and its loadagent back-end, the run
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20 time of a flash dump operation depends only on the serial baud rate and the
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21 size of the flash area to be dumped; it should not depend on the USB-serial
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22 adapter type or any host system properties, as long as the host system and
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23 serial adapter combination supports the desired baud rate. In contrast, flash
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24 programming and fc-xram loading operations are quite different in that their
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25 run times do depend on the host system and USB-serial adapter or other serial
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26 port hardware - this host system dependency exists because of the way these
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27 operations are implemented in our architecture.
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29 Flash programming operations
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30 ============================
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31
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32 Here are some examples of expected flash programming times, all obtained on the
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33 Mother's Slackware 14.2 host system:
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34
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35 Flashing an Openmoko GTA02 modem (K5A3281CTM flash chip) with a new firmware
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36 image (2376448 bytes), using a PL2303 USB-serial cable at 115200 baud: 0m19s to
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37 erase 37 sectors, 3m45s to program the image.
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39 Flashing the same OM GTA02 modem with the same fw image, using a CP2102
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40 USB-serial cable at 812500 baud: 0m19s to erase, 0m51s to program.
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42 Flashing a Magnetite hybrid fw image (2378084 bytes) into an FCDEV3B board
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43 (S71PL129N flash chip) via an FT2232D adapter at 812500 baud: 0m24s to erase
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44 13 sectors (4 small and 9 large), 1m27s to program the image.
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46 Regardless of whether you execute these two steps separately or use one of our
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47 new flash e-program-{bin,m0,srec} commands, flash programming is always done in
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48 two steps: first the erase operation covering the needed range of sectors, then
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49 the actual programming operation that includes the data transfer.
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51 Flash erase times are determined entirely by physical processes inside the
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52 flash chip and thus should not be affected by software design or the serial
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53 link: for each sector to be erased, fc-loadtool issues the sector erase command
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54 to the flash chip and then polls the chip for operation completion status; the
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55 polling is done over the serial link and thus may seem very slow, but the extra
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56 bit of latency added by the finite polling speed is still negligible (at least
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57 on the Mother's Slackware system) compared to the time of the actual sector
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58 erase operation inside the flash chip. One remaining flaw is that in our
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59 current implementation the issuance of each individual sector erase command to
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60 the flash chip takes 6 command-response exchanges between fc-loadtool and
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61 loadagent; on my Slackware host system this extra overhead is still negligible
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62 compared to the 0.5s or more for the actual erase operation time, but this
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63 overhead may become more significant on host systems with higher latency.
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65 After the erase operation, the execution time of the main flash programming
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66 operation is a sum of 3 components:
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68 * The time it takes for the bits to be transferred over the serial link;
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69 * The time it takes for the flash programming operation to complete on the
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70 target (physics inside the flash chip);
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71 * The overhead of command-response exchanges between fc-loadtool and loadagent.
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72
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73 Because image data transfer is taking place in this step, flash programming at
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74 812500 baud is faster than 115200 baud, although it is not the same 7x
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75 improvement as happens with flash dumps. The present version of fc-loadtool
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76 also uses a new binary transfer protocol instead of the hex-based one used in
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77 previous versions (prior to fc-host-tools-r13); this change produces a 2x
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78 improvement for OM GTA02 flashing, but only a smaller improvement for FCDEV3B
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79 flashing.
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80
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81 Notice the difference in flash programming times between GTA02 and FCDEV3B: the
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82 fw image size is almost exactly the same, any difference in latency between
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83 CP2102 and FT2232D is less likely to produce such significant time difference
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84 given our current 2048 byte transfer block size (in fact fc-xram transfer times
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85 suggest that FT2232D is faster), thus the difference in physical flash program
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86 operation times between K5A3281CTM and S71PL129N flash chips seems to be the
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87 most likely explanation.
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88
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89 It also needs to be noted that in the current version of fc-loadtool there is
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90 no difference in performance between flash program-bin, program-m0 and
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91 program-srec operations: they all use the same binary protocol with 2048 byte
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92 transfer block size. There is no coupling between source S-records and flash
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93 programming operation blocks (2048-byte units) in the case of flash program-m0
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94 and program-srec: the new implementation of these commands prereads the entire
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95 S-record image as a separate preparatory step on the host side, the bits to be
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96 programmed are saved in a temporary binary file (automatically deleted
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97 afterward), and the actual flash programming operation proceeds from this
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98 internal binary source - but it knows about any discontiguous program regions
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99 and skips the gaps properly.
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100
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101 XRAM loading via fc-xram
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102 ========================
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103
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104 The new version of fc-xram as of fc-host-tools-r13 is dramatically faster than
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105 the original implementation from 2013, using a new binary transfer protocol.
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106 The speed increase comes from not only switching from hex to binary, but even
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107 more so from eliminating the command-response turnaround time on every S3
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108 record. The new XRAM loading times obtained on the Mother's Slackware 14.2
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109 host system are:
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110
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111 Pirelli DP-L10 with built-in CP2102 USB-serial chip, 812500 baud, loading
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112 hybrid-vpm fw build, 49969 S3 records: 0m27s
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113
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114 FCDEV3B interfaced via FT2232D adapter, 812500 baud, loading hybrid fw build,
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115 78875 S3 records: 0m35s
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117 With the previous version of fc-xram these two loads took 1m40s and 2m54s,
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118 respectively. With the current version of loadtools XRAM loading is faster
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119 than flash programming for the same fw image as one would naturally expect (the
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120 flash programming step on the target is replaced with a simple memcpy()
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121 operation), but in the previous version XRAM loading was slower because of
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122 massive command-response exchange overhead: there was a command-response
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123 turnaround time incurred for every S3 record, typically carrying only 30 bytes
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124 of payload.
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125
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126 Additional complication with FTDI adapters and newer Linux kernel versions
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127 ==========================================================================
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128
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129 If you are using an FTDI adapter and a Linux kernel version newer than early
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130 2017 (the change was introduced between 4.10 and 4.11), then you have one
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131 additional complication: a change was made to the ftdi_sio driver in the Linux
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132 kernel that made many loadtools operations (basically everything other than
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133 flash dumps which are entirely target-driven) unbearably slow, at least with
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134 previous versions of loadtools that made many more command-response exchanges
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135 with loadagent for smaller transfer units and thus were much more sensitive to
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136 host system latency on these exchanges. We do not yet know if this FTDI
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137 latency timer issue still has a significant negative impact or not with current
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138 loadtools, but if it does, the solution is to run a special setserial command.
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139 After you plug in your FTDI-based USB-serial cable or connect the USB cable
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140 between your PC or laptop and your FTDI adapter board, causing the
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141 corresponding ttyUSBx device to appear, execute the following command:
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142
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143 setserial /dev/ttyUSBx low_latency
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144
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145 (Obviously change ttyUSBx to your actual ttyUSB number.) Execute this
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146 setserial command before running fc-loadtool or fc-xram, and then hopefully you
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147 should get performance that is comparable to what I get on classic Slackware.
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148 I say "hopefully" because I am not able to test it myself - I refuse to run any
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149 OS that can be categorized as "modern" - but field reports of performance on
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150 non-Slackware systems running newer Linux kernels (4.11 or later) are welcome,
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151 both with and without the low_latency setting. Please be sure to include your
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152 Linux kernel version and your USB-serial adapter type in your report!