annotate doc/FTDI-EEPROM-tools @ 68:72ff023ec6c9

doc/Luna-LCD-cable: written in preparation for making this cable
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 01 May 2020 03:18:08 +0000
parents 311c800268b8
children 0514e3520be3
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1 Mother Mychaela has developed a set of Linux command line tools for manipulating
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2 configuration EEPROMs that are attached to FT2232x devices and accessed in-band
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3 via USB. This document describes these tools.
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4
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5 Supported FTDI chips and EEPROMs
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6 ================================
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7
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8 The present tools work with 93C46, 93C56 and 93C66 EEPROMs attached behind
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9 FT2232x dual-channel UART/FIFO/MPSSE/etc chips, both FT2232C/D and FT2232H.
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10 We can read these EEPROMs for examination or backup, and we can program them
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11 with new bits, either restoring a previously saved backup or creating a new
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12 from-scratch configuration. These EEPROM configurations (which we can save,
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13 restore or create from scratch) set the USB VID:PID and the textual strings
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14 naming the manufacturer, the product model and an optional serial number,
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15 select whether each FT2232x channel will come up in the default UART mode or
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16 one of the other EEPROM-configurable modes (245 FIFO, CPU-style FIFO or fast
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17 opto-isolated serial), and allow a few other obscure chip settings to be
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18 tweaked.
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19
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20 Some work has also been done toward the goal of being able to program the
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21 internal EEPROM in FT232R chips (a very popular single-channel USB to UART
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22 converter needing no external components), but this work has not been finished
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23 yet, and the present tools should NOT be used to attempt an EEPROM write on
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24 that chip - the risking of bricking the chip is too high.
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25
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26 More generally, our fteeprom-read tool should be able to read out the EEPROM
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27 content from just about any FTDI chip including FT232R, whereas our
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28 fteeprom-prog tool should be able to program a user-supplied set of bits into
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29 any FTDI+EEPROM combo where the EEPROM is a separate chip - but it is NOT safe
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30 to use on FTDI chips like FT232R or FT-X that have their EEPROM built in.
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31 Furthermore, if the goal is to generate a new EEPROM config from scratch, as
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32 opposed to restoring a saved backup, we currently have generators only for
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33 FT2232C/D and for FT2232H. (We also have a generator program for FT232R, but
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34 it is of no use for as long as fteeprom-prog is not safe to use on FT232R
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35 chips.)
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36
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37 libftdi dependency
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38 ==================
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39
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40 We use libftdi (which is in turn layered on libusb) to issue the special USB
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41 control pipe commands to FTDI chips which are needed to read and write their
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42 EEPROMs. We use old-style libftdi-0.x (-lftdi on the link line) as opposed to
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43 libftdi1 (-lftdi1) because the new versions took away the ability to write to
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44 the EEPROM directly with ftdi_write_eeprom_location() calls, forcing users to
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45 go through libftdi1's own EEPROM smarts, which we don't want to do - our tools
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46 are all about more direct user empowerment at the lowest level.
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47
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48 Selecting the device to operate on
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49 ==================================
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50
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51 Our fteeprom-read, fteeprom-prog and fteeprom-erase tools take a device selector
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52 argument, selecting the device to operate on. This required argument is the
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53 string to be passed to the ftdi_usb_open_string() function in libftdi, allowing
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54 the device to be operated on to be selected in one of several ways. Copying
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55 from libftdi documentation, the available formats are:
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56
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57 d:<devicenode> - path of bus and device-node (e.g. "003/001") within usb device
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58 tree (usually at /proc/bus/usb/)
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59
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60 i:<vendor>:<product> - first device with given vendor and product id, ids can
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61 be decimal, octal (preceded by "0") or hex (preceded by "0x")
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62
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63 i:<vendor>:<product>:<index> - as above with index being the number of the
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64 device (starting with 0) if there are more than one
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65
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66 s:<vendor>:<product>:<serial> - first device with given vendor id, product id
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67 and serial string
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68
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69 If you have only one FTDI device connected to your PC or laptop at the time of
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70 your EEPROM manipulation session (generally a good idea to avoid hitting the
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71 wrong device by mistake) and if that FTDI device has some sensible starting
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72 USB VID:PID (either from the previous EEPROM config or the chip's sans-EEPROM
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73 default) that doesn't clash with anything else, then the i: form will probably
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74 be the most convenient, e.g.:
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75
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76 i:0x0403:0x6001 for single-channel FT232x devices running with the default ID
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77 i:0x0403:0x6010 for dual-channel FT2232x devices running with the default ID
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78 i:0x0403:0xPPPP for custom PIDs assigned out of FTDI's VID range
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79 i:0xVVVV:0xPPPP for totally custom USB IDs
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80
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81 Or if the current device config is totally hosed (the EEPROM has a passing
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82 checksum, but sets some completely bogus USB ID), then the d: form will
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83 probably be required for recovery.
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84
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85 Reading the EEPROM
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86 ==================
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87
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88 The basic EEPROM read command is as follows:
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89
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90 fteeprom-read <device-selector>
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91
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92 See the previous section for the device selector argument. In this default
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93 form the tool will read the first 64 EEPROM words, which is appropriate for
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94 93C46 external EEPROMs or for the internal 1024-bit EEPROM in the FT232R chip.
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95 However, if you are working with an FT2232x board with an external EEPROM and
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96 that EEPROM is of a larger variety (93C56 or 93C66), this basic form with give
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97 you an incomplete (truncated) read, and you will need one of the following
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98 extended forms to read the complete EEPROM:
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99
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100 fteeprom-read -b <device-selector> -- read 128 EEPROM words (93C56)
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101 fteeprom-read -B <device-selector> -- read 256 EEPROM words (93C66)
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102
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103 (If you use one of the extended forms on a smaller EEPROM, you will get 2 or 4
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104 copies of the same bits.)
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105
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106 The output of fteeprom-read is in the same format as the input to fteeprom-prog,
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107 thus you can redirect the output to a file and get a restorable backup copy of
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108 your EEPROM.
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109
49
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110 It also needs to be noted that if the FTDI device has the kernel's ftdi_sio
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111 driver attached to it (ttyUSB device present) when you run fteeprom-read (same
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112 for fteeprom-prog and fteeprom-erase), the act of running any of our EEPROM
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113 tools will cause it to unbind, i.e., the ttyUSB device will disappear. If the
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114 device being operated on is a dual-channel FT2232x, then only the ttyUSB device
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115 corresponding to Channel A will disappear, while the Channel B ttyUSB device
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116 will stay.
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117
45
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118 Programming the EEPROM
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119 ======================
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120
49
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121 In terms of the primitives provided over USB, writing to EEPROMs sitting behind
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122 FTDI chips is accomplished by writing one 16-bit word at a time: the
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123 SIO_WRITE_EEPROM_REQUEST command writes a user-supplied word at a user-supplied
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124 EEPROM address. However, our fteeprom-prog tool currently supports only writing
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125 complete EEPROMs (64 or 128 or 256 16-bit words starting at address 0) and we
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126 do not currently provide any kind of "random access write" utility; the primary
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127 reason for this design decision is practical usefulness: FTDI's EEPROM structure
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128 includes a checksum over the first 64 words for 1024-bit EEPROMs or over the
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129 first 128 words for larger ones, and if this checksum fails to match, the entire
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130 structure is deemed to be invalid - hence there is no practical use case for
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131 selectively rewriting individual words. The only exception may be with 93C66
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132 EEPROMs: on these giants only the first half would be subject to the checksum,
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133 and the second half could be used arbitrarily. However, we have not yet
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134 encountered any boards out in the wild with such big EEPROMs, and we have no
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135 plans to use such in any of our own hardware designs either, hence there is no
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136 business case at the present moment to develop tooling support for them.
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137
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138 There are two primary modes of usage for our fteeprom-prog tool: restoring a
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139 saved EEPROM backup or writing a new EEPROM config which you generate yourself.
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140 To restore a saved EEPROM backup, run the tool as follows:
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141
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142 fteeprom-prog <device-selector> <eeprom-image-file>
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143
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144 To program a new EEPROM config of your own, run a pipeline of this form:
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145
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146 <generator-tool> | fteeprom-prog <device-selector>
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147
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148 fteeprom-prog reads the EEPROM image from stdin if no image file is named on
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149 the command line; the image format is the same in both cases, and the length of
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150 this EEPROM image tells the tool how many words need to be programmed - there
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151 are no -b or -B options to fteeprom-prog.
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152
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153 Generator tools
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154 ===============
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155
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156 Unfortunately FTDI never documented the format of their EEPROM configuration
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157 structure - apparently they consider it a proprietary trade secret just like
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158 the wire protocol spoken over USB between their chips and their closed-source
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159 proprietary drivers. All FOSS community support for these chips is based on
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160 reverse engineering, and that includes the EEPROM format.
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161
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162 The present suite of tools includes ftee-gen2232c and ftee-gen2232h EEPROM image
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163 generators, meant for use with FT2232C/D and FT2232H chips, respectively. These
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164 tools are based on the knowledge extracted from other (pre-existing) community
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165 tools, primarily the EEPROM config code built into various libftdi versions -
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166 we haven't done any FTDI RE of our own, instead the goal of this project has
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167 been to create a set of tools that are better fit for production use.
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168
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169 Our ftee-gen2232c and ftee-gen2232h tools are invoked as follows:
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170
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171 ftee-gen2232[ch] [-b|-B] <config-file> [serial-num]
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172
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173 The output of these generator tools is meant to be piped directly into
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174 fteeprom-prog.
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175
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176 The philosophy of which settings are given in the config file vs. which ones
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177 are given on the command line reflects configuration management and factory
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178 production line operations. In the envisioned usage there would be a config
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179 file for each product, giving the USB VID:PID, textual manufacturer and product
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180 ID strings and possibly other config settings which need to be changed from the
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181 defaults, but the optional serial number string is given on the command line
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182 because it would be different for each individual unit being programmed.
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183
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184 The EEPROM size selection is also made on the command line, so that the same
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185 config can be programmed into a smaller EEPROM or a bigger one. By default our
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186 tools generate an image suitable for a 93C46 EEPROM: the generated image is 64
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187 words long, with a checksum in word 63, and the EEPROM type byte in FTDI's
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188 structure is set to 0x46. Running with -b produces an image for a 93C56 EEPROM:
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189 the EEPROM type byte is set to 0x56, and the checksum-covered image length is
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190 extended to 128 words. Finally, -B sets things up for a 93C66 EEPROM: the
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191 EEPROM type byte is set to 0x66, but the generated checksum-covered image is
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192 still 128 words long just like with -b, as that is what FT2232x chips apparently
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193 expect. I said "apparently" because I don't have any FT2232x hardware with
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194 93C66 EEPROMs and I don't plan on acquiring or building any, hence this minimal
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195 93C66 support is completely untested - use at your own risk.
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196
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197 It also needs to be noted that with our current RE-based understanding of FTDI's
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198 undocumented EEPROM structure, using a bigger EEPROM does NOT provide more room
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199 for strings: all that happens with -b and -B options is that a gap of 64 unused
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200 EEPROM words is inserted between the end of the fixed structure and the
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201 beginning of strings. The exact same arrangement has been observed in all 93C56
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202 EEPROM images found in the wild, presumably produced with FTDI's official tools,
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203 including FTDI's own USB-COM232-PLUS2 board - thus it is not clear at all if
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204 FT2232x chips actually support longer strings with bigger EEPROMs, and if not,
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205 what does one need a bigger EEPROM for...
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206
49
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207 For the format of config files read by our ftee-gen2232[ch] tools and what
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208 settings can be tweaked, read the source code.
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209
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210 Erasing the EEPROM (making it blank)
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211 ====================================
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212
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213 If you are playing with a "generic" FT2232x breakout board that is made for
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214 tinkering, as opposed to a more finished product, such boards are typically
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215 shipped with their EEPROMs completely blank. In that case restoring the EEPROM
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216 to its "pristine" state after playing around would mean erasing it, i.e.,
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217 bringing it into a blank (all ones) state. FT2232x chips provide two ways to
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218 do so: one can explicitly write 0xFFFF into each individual EEPROM word with
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219 SIO_WRITE_EEPROM_REQUEST, or one can send a SIO_ERASE_EEPROM_REQUEST command to
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220 the chip, and the chip then erases the entire EEPROM. But we don't know how
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221 the latter SIO_ERASE_EEPROM_REQUEST operation is implemented by FT2232x chips:
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222 does the FT2232x chip go through and erase each word individually, or does it
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223 issue an "erase full chip" opcode to the serial EEPROM? If the latter, then
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224 according to some EEPROM datasheets that operation may not work if the EEPROM
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225 is powered from a 3.3V rail rather than the full USB 5V - may be an issue in
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226 FT2232H-based designs.
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227
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228 In any case our tools provide both ways. To perform the "automatic full chip
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229 erase" operation, run the following command:
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230
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231 fteeprom-erase <device-selector>
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232
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233 To blank the EEPROM by writing 0xFFFF into each word, run one of the following
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234 pipelines:
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235
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236 ftee-mkblank | fteeprom-prog <device-selector> -- blank a 93C46 EEPROM
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237 ftee-mkblank -b | fteeprom-prog <device-selector> -- blank a 93C56 EEPROM
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238 ftee-mkblank -B | fteeprom-prog <device-selector> -- blank a 93C66 EEPROM