On Mon, 2011-07-04 at 16:43 +0200, Uwe Bonnes wrote:
> >>>>> "Alex" == Alex Stefan <alexandru.stefan@xxxxxxxxxxx> writes:
>
> Alex> On Tue, 2011-06-28 at 15:06 +0200, Uwe Bonnes wrote:
> >> >>>>> "Alex" == Alex Stefan <alexandru.stefan@xxxxxxxxxxx> writes:
> >>
> Alex> Hello, I am working on implementing a SPI protocol using
> Alex> bit-banging on the CBUS interface of a FT232H chip. The purpose
> Alex> would be to program another chip's flash memory via USB.
> >>
> Alex> The one I can't figure out is how to correctly time the SPI
> Alex> operations. I mean, how can I output a precise clk signal on SCK
> Alex> using bit-banging.
> >> Why do you want do bitbang with the FT232H? MPSSE mode is much
> >> easier to use.
> >>
> >> Bye
>
> Alex> I need to use CBUS bitbang because the MPSSE pins will be used for
> Alex> UART communication afterwards.
>
> Alex> Anyway, I have implemented everything, works correctly, but not
> Alex> fast enough. My SPI tx/rx function runs at an approximate rate of
> Alex> 300 BPS which translates into a huge amount of time to flash a 30
> Alex> KB image to the chip.
>
> Alex> Has anyone encountered this problem so far? From what I can tell,
> Alex> the problem is with the USB driver functions in the kernel, but I
> Alex> can't figure out how to solve it. Any ideas?
>
> If you don't need UART and SPI at a time, which is not possible with the
> single channel FT232H, consider multiplexing the MPSSE pins and some
> non-MPSSE pin as multiplexer control.
>
> How did you implement SPI. Do you assemble large transfer trunks and read
> back large traunks or do you send small chunks and read often? Remember that
> USB is manged by 1 ms/125 us Frames and each write/read transaction takes at
> least one or two frames.
>
> Otherwise, does the FTDI libspi also work with bitbanging? What is the speed
> of that solution.
>
Thanks for your reply.
It's not my call whether to connect the SPI and UART together on the
MPSSE port. I will forward your suggestion.
>From what I saw in the CBUS bitbang examples of the libftdi library, I
can't make use of any "buffering" system and I must make a call to
'ftdi_set_bitmode()' everytime I need to chage the state of a pin.
I have talked to the developers of FTDI lipspi and they said that their
current version only supports MPSSE SPI, not bit-banging.
Could you please offer some more details on the USB timing? How can I
set the interval between 2 USB frames (from 1ms to 125 uS) ?
Regards,
Alex
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