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cp2102-decode-ee-desc: decode endpoint descriptors
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 27 Sep 2023 20:00:56 +0000
parents 742c41f44658
children
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742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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1 Q: How do various standard software components (ftdi_sio driver in the Linux
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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2 kernel, libftdi etc) identify what kind of FTDI chip they are talking to?
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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3 For example, how do they tell apart between FT2232C/D and FT2232H with their
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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4 respective differences in features and capabilities?
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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5
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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6 A: They look primarily at the bcdDevice word in the USB device descriptor. One
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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7 can also look at bNumInterfaces in the configuration descriptor (more
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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8 reliable, as will be seen momentarily) to distinguish between single-channel
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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9 vs dual-channel vs 4-channel devices, but bcdDevice is still the only way to
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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10 tell apart between FT232BM and FT232R, or between FT2232C/D and FT2232H.
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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11
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Mychaela Falconia <falcon@freecalypso.org>
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12 However, this all-important bcdDevice word exhibits a very noteworthy quirk: it
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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13 is included in FTDI's EEPROM configuration structure, thus it can be overridden
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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14 through EEPROM programming. The result is that at least on some FTDI chips (so
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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15 far I've only tested this quirk on FT2232D) one can make the chip report a
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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16 different bcdDevice code than its true chip version, and thus fool standard
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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17 host software! Needless to say, doing so is a very bad idea: the actual
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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18 behavior of the chip, the way it acts upon various bits in the EEPROM config
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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19 structure and the way it reacts to various USB commands, does not change just
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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20 because you changed the "device release number" code, thus various host control
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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21 functions will start misbehaving and failing in mysterious ways.
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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22
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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23 Our FTDI EEPROM tools (see FTDI-EEPROM-tools article) often need to know what
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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24 kind of FTDI chip you are working with as in reading, programming or preparing
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Mychaela Falconia <falcon@freecalypso.org>
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25 an EEPROM image for. Most competitor tools (for example, the ones integrated
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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26 into libftdi) do the same thing as all other standard host software components:
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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27 they look at the reported bcdDevice and use this code to decide what kind of
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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28 FTDI chip they are working with - hence they will be misled and broken if this
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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29 word is misprogrammed in an EEPROM. To avoid this issue, our FTDI EEPROM tools
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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30 follow a different design: with our tools you as the operator are responsible
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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31 for knowing what kind of FTDI chip you are working with - our tools do NOT
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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32 attempt to autodetect the chip, as it is impossible to do so in an environment
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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33 that may include badly corrupted or misprogrammed EEPROMs. Specifically, you
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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34 are responsible for manually selecting the correct generator tool (for example,
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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35 ftee-gen2232c vs ftee-gen2232h in the case FT2232x) and manually specifying
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Mychaela Falconia <falcon@freecalypso.org>
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36 your EEPROM size with -b or -B options if you are working with a board design
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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37 that uses a 93C56 or 93C66 EEPROM.
742c41f44658 doc/FTDI-chip-ID: new article
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38
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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39 This largely-manual design of our FTDI EEPROM tools makes them less friendly to
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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40 casual users, but in return they should be able to recover from any possible
742c41f44658 doc/FTDI-chip-ID: new article
Mychaela Falconia <falcon@freecalypso.org>
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41 EEPROM corruption or misprogramming, accidental or malicious.