On 16/02/17 07:34, Sascha Hauer wrote:
Hi Antony,
On Wed, Feb 15, 2017 at 10:12:25AM +0300, Antony Pavlov wrote:
This patch series makes it possible to use FT2232H ACBUS[7:0]
pins as gpio pins from sandbox barebox.
I have tested output gpio functionality by connecting
a LED to ACBUS[0] and lightening it with gpio_direction_output
and gpio_set_value barebox commands.
Also I have performed input test with ACBUS[0] -> ACBUS[1] loopback.
The main goal of adding gpio functionality to sandbox barebox
is using it for connecting real i2c and spi devices to sandbox barebox
(not tested yet).
I just read that the FT2232H can even do native I2C and SPI, so no gpio
bitbanging would be necessary. Would it be possible to use this mode
instead?
Otherwise I think there should be a possibility to specify which, if
any, FT2232H chip barebox uses.
The MPSSE mode of the FT2232H can sort of do native I2C, but not in a
strictly conforming way. The I2C SDA needs to be connected to two pins
on the FT2232H, one for output and one for input, and there is a
"Drive-Only-Zero" option for the output to ensure it is only driven low,
and tri-stated high. However, the I2C SCL is only connected to an
output pin on the FT2232H, and is always driven in both directions.
Therefore, it does not support "clock-stretching" by I2C slaves (where a
slave pulls the SCL line low until it is ready), because it cannot read
back the state of the SCL line. Worse, if an I2C slave is doing
clock-stretching by driving SCL low, this will contend with the FT2232H
driving SCL high at the same time.
--
-=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@xxxxxxxxx> )=-
-=( Web: http://www.mev.co.uk/ )=-
_______________________________________________
barebox mailing list
barebox@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/barebox
