On Tuesday 23 June 2009, Magnus Lundin wrote: > > Though for the record ... the "bitbang" protocol > > for FT232 (not FT2232) is neither well-known nor open. > > > > If that were open, it would be possible to implement > > JTAG on other FTDI chips. Less efficiently, to be > > sure, but with easier 1.8V compatibility. > > > > - Dave > > > I call BS. > > Do you know JTAG over FT232 ? Somer folks called you USB expert.
I've had to do SPI over FT232 and that's where I noticed that the documentation was seriously lacking. You can view JTAG as a combination of: (a) state transitions driven by TMS + TCK (b) SPI (TMS == chipselect) in the xRSHIFT states > The protocols available for FT232 are well published, it is not hard but > unpleasant to implement JTAG on them, that is what interfaces like the > Altera USB Blaster does. If they are "well published" that's news to me. I found significant holes. One example is just the differences between the FT232B and FT232R revisions. I think it was winter 2006-2007 where I did that; maybe docs have been fixed since then. The "Official Answer" from FTDI was to use D2XX library. Any "well published" docs related to that library, not to commands at the chip level. I suppose I could have stuck a USB sniffer on the wire and watched what their library did with each API call. The need for that level work highlights the doc holes > But JTAG over MPSSE is soo much nicer that nobody who has worked with > this wants to go back to FT232 (without the extra 2), it is not a > tecnical problem it is just a PITA. Agreed, JTAG over MPSSE is better. And a part of that is that the docs actually cover all the registers and commands you can issue, so you're not left guessing. - Dave _______________________________________________ Openocd-development mailing list Openocd-development@lists.berlios.de https://lists.berlios.de/mailman/listinfo/openocd-development
