iMx6Solo SPI interface: No data read on MISO

[hardyb]

Hello,

I have setup SPI in Linux with an iMx6Solo Wandboard on a custom carrier board. I am trying to establish communication with a peripheral. However, I never see any data come back from the MISO line.

MOSI line, clock and chip select all have good transitions and I have scoped the data coming back on MISO to confirm it's being sent. On the iMx6 [master], the IRQ goes off but I only ever get a blank buffer reported. I have used the user-space tools spi-pipe & spi-config as well as the Ruby SPIDev gem. Same result with both.

I am inclined to believe this might be an issue with either spi_imx, spidev or both. Perhaps one reads the data and clears the buffer before the other can retrieve the data for my application? Or there's a hand-off that's mistimed/failing?

I am using the SPI1 interface. I am confident my DTS entries and pin assignments are correct.

System, drivers and software courtesy of the Freescale BSP on Yocto, Krogoth branch.

Any questions or insight appreciated. Thanks.

[hardyb · Accepted solution]

This issue was the result of a bad connector on our carrier board. We were not able to source an EDM connector and used a different adapter that was deeper than the EDM specification. This caused the processor module board to have half of its pins unconnected to the carrier. Only a few connections went through that side of the adapter so it took us a while to diagnose.

[igorpadykov]

Hi Hardy

MISO data should be provided by external device, so one can check

if it was configured properly. Also one can test with loopback test.

Best regards
igor
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[hardyb]

MOSI, MISO, clock and chip select have all been confirmed via logic analyzer.

The slave device is an FPGA and is currently programmed to respond to any data on the MOSI line. I see the responses through a logic analyzer on the MISO line, but the buffer comes back 0 through Ruby SPIDev and spi-pipe.

I have not tried the loopback test. That is a good idea, I will attempt to set that up tomorrow.