SPI0 data in corrupt

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Joe Phaneuf

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Nov 14, 2016, 5:49:28 PM11/14/16

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Cross posting from seeed forums, no responses there.

If anyone has had any success whatsoever using spi0 on a beagle bone green wireless, would love to hear about it.

tldr: clocking in data on spi0 looks cattywompus, spi1 ok

Was noticing an issue with some custom hardware/software that utilizes both spi channels, was working on beaglebone black prior. Wanted to make it easily reproducible so flashed a bbgw and used adafruit bbio library as an example.

steps:

1.) flash BBGW with latest production image 4.4.15-ti-r37 (tested on 4.1 kernel, and some other images that I forgot to document as well)

2.) prevent sound drivers from loading, as they conflict with spi1:

cd /lib/modules/4.4.15-ti-r37/kernel/sound/core
mv snd.ko snd.ko.bkp

3.) install adafruit library from source (need latest greatest, pip upgrade didn't work)

cd ~
git clone https://github.com/adafruit/adafruit-beaglebone-io-python.git
cd adafruit-beaglebone-io-python
python setup.py install
cd ..

4.) use wires to loopback MOSI to MISO, both channels

short P9.18 and P9.21 with a piece of wire (SPI0)

short P9.29 and P9.30 with a piece of wire (SPI1)

5.) put the following into a file and run it

from Adafruit_BBIO.SPI import SPI
def run(x,y):
print 'running spi {} {}'.format(x,y)
spi = SPI(x,y)
spi.mode=2
spi.msh=4000000
bytes2send = range(20)
print 'sending {}'.format(bytes2send)
print spi.xfer2(bytes2send)
spi.close()
run(0,0)
run(1,0)

result:

sending [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

[128, 7, 28, 31, 112, 231, 124, 127, 192, 135, 156, 159, 240, 231, 252, 255, 0, 7, 28, 31]

running spi 1 0

sending [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

so, spi1 works in loopback. spi0...wtf? there are places where it looks like it's double clocking MISO (like a 0x00000001 becomes a 0x00000011), some of it just looks random. Works fine on beaglebone black.