On Mon, Jul 11, 2011 at 10:33 AM, brunosmmm <brunosmmm@xxxxxxxxx> wrote:
> Well, i've seen enough examples and implementations of SPI communications
> using FT2232H / libftdi.
> The problem is that the most common approach i've seen in all these example
> / implementations is as follows: one has a read / write function to which is
> passed the data to write, then it asserts CS / writes the command to the
> device. After this, it performs a bulk read with libftdi, obtaining the data
> and only after this CS is de-asserted. That makes no sense for me, as this
> approach wastes a LOT of time waiting for the data to arrive (latency timer
> and bulk transfers).
That is okay, right? The key is to pack as many commands as possible
together to minimize the latency.
> If we have an internal buffer on the chip, why use this approach? So, I
> started modifying this a little so that only a sequence of commands which
> include write/read is passed to the 2232h, and after a while I would go and
> collect the contents of the chip's buffer.
>
> I have to do this, as the task i'm trying to do is collect a few (3) bytes
> at somewhat regular intervals from a SPI slave, and as the collection speeds
> rise, it becomes impractical to use the "standard" approach i mentioned.
>
> Well, the problem is that i seem to be getting a lot of trash along with the
> data when i do a full buffer read. I have no idea why, as i never execute
> any other read commands that could make the chip put data into its buffer.
Probably those are the two bytes response from the chip.
> I know this is not the best way to collect this data, but i'm avoiding as
> much as possible a microcontroller / fpga data buffering alternative.
>
> That said, any comments and/or suggestions that could help me? Thanks in
> advance
You can probably check out some examples.
http://flashrom.org/trac/flashrom/browser/trunk/ft2232_spi.c
http://code.google.com/p/libftdispi/
--
Xiaofan
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