FreeCalypso > hg > freecalypso-hwlab
diff doc/FT232R-notes @ 173:df4bf4e06221
doc: several articles moved to other repositories
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Mon, 11 Sep 2023 06:51:05 +0000 |
parents | 026dd69e4ebb |
children |
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--- a/doc/FT232R-notes Mon Sep 11 05:24:26 2023 +0000 +++ b/doc/FT232R-notes Mon Sep 11 06:51:05 2023 +0000 @@ -1,42 +1,3 @@ -Unlike FT2232x devices with external EEPROMs, an FT232R device is not expected -to ever have a blank EEPROM in normal usage: these chips have their EEPROM -built in, and FTDI probably ships them with this internal EEPROM already -programmed. I said "probably" because I have not yet had an occasion to build -my own FT232R-containing board where I would be getting completely pristine -"bare" chips from Digi-Key, thus I have no first-hand verified knowledge. - -As an experiment, I have programmed "blank" (0xFFFF in every word) images into -the two FT232R devices I have available for play at the moment (specifically -devices which I could afford to brick if things went badly), and FT232R behaves -the same way as FTDI's earlier chips with external EEPROMs: it runs with a fixed -default config when the EEPROM is invalid. But this configuration is NOT -recommended for production use - you should always have a valid EEPROM config -in your FT232R chip. +This article has moved; the new location is: -When our FreeCalypso fteeprom tools were first put together in 2019-04, I was -getting erratic behaviour: when I tried to program my own EEPROM config -generated with ftee-gen232r, the resulting EEPROM content became a bitwise AND -between the previous image and the new one, as if the "EEPROM" is not really an -erasable memory, but one of OTP kind where ones can be turned into zeros, but -not the other way around. I was doing this experiment on a no-name FT232RL -adapter from ebay, thus my first thought was that the FT232RL chip was bad, a -less-than-perfect clone rather than genuine FTDI. But then I bought a UB232R -module from Digi-Key (presumably containing a genuine FT232RQ chip), and it -behaved the same way. - -Further investigation revealed that FT232R EEPROM write operations work -correctly only if they are preceded by this magic sequence: - - ftdi_usb_reset(&ftdi); - ftdi_poll_modem_status(&ftdi, &modem_status); - ftdi_set_latency_timer(&ftdi, 0x77); - -I can see how FTDI could have reasonably implemented a sort of safety lock on -their EEPROM write operations, allowing them only if a special unlock sequence -has been given - but it completely baffles me why they are doing some sort of -OTP emulation in the absence of the right magic sequence, as opposed to -disabling EEPROM writes altogether. It is worth noting that this magic sequence -is NOT needed for programming external EEPROMs behind FT2232x chips - were FTDI -folks being deliberately malicious in designing their FT232R chip to simulate -appearance of being bricked when it is programmed with older (or third-party) -software tools that don't know the new magic sequence? Who knows... +https://www.freecalypso.org/hg/fc-usbser-tools/file/tip/doc/FT232R-notes