On 01/25/12 01:11, bruce_leon...@selinc.com wrote:
Good afternoon,
I'm using the 3.0.3 kernel running on an MPC8308 and am trying to
interface to a Cypress CY14B256Q2A non-volatile RAM via SPI. I've got the
SPI infrastructure, the Freescale SPI driver (drivers/spi/spi_fsl_spi.c),
and spidev built into the kernel and everything on the user space/kernel
side appears to be working correctly (at least when I try to read the
NvRAM's config register all the right places in the kernel get hit and I
see the SPI signals active with an o-scope).
I think what I'm hitting is a lack of understanding/documentation on the
SPI controller in the 8308. To read data from the NvRAM, the Master (the
8308 in this case) needs to clock out a byte long "read" command, two
bytes of address, and then clock in the data from the NvRAM. However, I
never get any data back. I think the problem is that (direct quote from
the 8308 reference manual) "SPICLK is a gated clock, active only during
data transfers". So once the read command and address are sent, the 8308
considers the data transfer complete and gates off SPICLK. Without
SPICLK, the NvRAM has no way to clock out it's data. I think it's ready
to, it just can't.
So the question is, how do I use spidev (or any other means) to get the
8308 SPI controller to keep SPICLK active so that the output data from the
NvRAM gets clocked out to the 8308?
Thanks.
Bruce
Did you see Documentation/spi/spidev_fdx.c:do_msg ?
it perform a full-duplex (actually half-duplex) 1 byte transfer.
In your case you need a transfer that outputs 3 bytes (read cmd + address)
and inputs 1? byte.
If you do it this way I would expect the SPICLK to be active
during the 2nd part of the transfer (whenever the CPU "reads" the
data from SPI client).
hth.
---
NvBolhuis
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
