"error return without exception set" then try to set cshigh to False.

oosavu commented 3 years ago

Raspberry PI Zero W.

Works good on Linux raspberrypi 4.19.75+ #1270 Tue Sep 24 18:38:54 BST 2019

Fails on Raspberry Pi OS (32-bit) Lite May 2020 (Release date:2020-05-27)

import spidev spi = spidev.SpiDev() spi.open(0, 1) spi.cshigh = False

JonathonReinhart commented 3 years ago

I think the problem is here: https://github.com/doceme/py-spidev/blob/a5d82b88bd1c95c9f9ec46e9f7afe08c3323e625/spidev_module.c#L904-L906

__spidev_set_mode returns -1 without calling PyErr_Set*, which is then returned by SpiDev_set_cshigh.

Running this test code:

#!/usr/bin/env python3
import spidev

spi = spidev.SpiDev()
spi.open(0, 0)

spi.cshigh = False

I see only these relevant syscalls in strace:

openat(AT_FDCWD, "/dev/spidev0.0", O_RDWR|O_LARGEFILE) = 3
ioctl(3, SPI_IOC_RD_MODE, 0xbea7c23f)   = 0
ioctl(3, SPI_IOC_RD_BITS_PER_WORD, 0xbea7c23f) = 0
ioctl(3, SPI_IOC_RD_MAX_SPEED_HZ, 0xbea7c248) = 0
ioctl(3, SPI_IOC_WR_MODE, 0xbea7d1d7)   = 0
ioctl(3, SPI_IOC_RD_MODE, 0xbea7d1db)   = 0

So because none of the ioctl calls fail, I have to assume that the attempt to set the SPI_CS_HIGH bit was refused by the kernel driver. So test, the readback value, didn't match mode, the value attempted to be set.

jfernandz commented 3 years ago

cshigh in fact is True by default because if you print(device.cshigh) you'll get a True, however I'm having a low-active behavior:

DS0003

Why is this?

HowardALandman commented 3 years ago

The SPI standard is that chip select should default to active-low. There are however a handful of chips that use active-high, so a general driver has to support that possibility.

Isn't this a 1-line fix? Why is it still open?

doceme / py-spidev

"error return without exception set" then try to set cshigh to False. #108