Comments (14)
pdp7
commented on July 21, 2024
I have added debug output to Adafruit_Blinka, Adafruit_CircuitPython_BusDevice, and py_spidev:
debian@beaglebone:~/Adafruit_CircuitPython_BME280$ sudo strace -f -o /tmp/strace.out python3 examples/bme280_simpletest.py
[sudo] password for debian:
spidev_module: SpiDev_init()
Adafruit_CircuitPython_BusDevice.__init__
Adafruit_CircuitPython_BusDevice.__init__: set self.chip_select = chip_select: P9_17
Adafruit_CircuitPython_BusDevice.__init__: set self.chip_select.value = True
Adafruit_CircuitPython_BusDevice.__init__: return
Adafruit_CircuitPython_BusDevice.__enter__
Adafruit_CircuitPython_BusDevice.__enter__: self.spi.configure()
Adafruit_CircuitPython_BusDevice.__enter__: set self.chip_select.value = False
Adafruit_CircuitPython_BusDevice.__enter__: return self.spi
generic_linux/spi.py: call self._spi.open(self._port, 0)
spidev_module: SpiDev_open(): enter
spidev_module: SpiDev_open(): call open(path, O_RDWR, 0)
spidev_module: SpiDev_open(): ioctl(self->fd, SPI_IOC_RD_MODE, &tmp8)
spidev_module: SpiDev_open(): ioctl(self->fd, SPI_IOC_RD_BITS_PER_WORD, &tmp8)
spidev_module: SpiDev_open(): ioctl(self->fd, SPI_IOC_RD_MAX_SPEED_HZ, &tmp32)
spidev_module: SpiDev_open(): return Py_None
generic_linux/spi.py: return from self._spi.open(self._port, 0)
generic_linux/spi.py: try: self._spi.no_cs
spidev_module: SpiDev_set_no_cs(): self->mode=0x1
spidev_module: SpiDev_set_no_cs(): SPI_NO_CS=0x40
spidev_module: SpiDev_set_no_cs(): set SPI_NO_CS bit
spidev_module: SpiDev_set_no_cs(): tmp=0x41
spidev_module: SpiDev_set_no_cs(): call __spidev_set_mode()
spidev_module: __spidev_set_mode(): fd=4
spidev_module: __spidev_set_mode(): mode=0x41
spidev_module: __spidev_set_mode(): call ioctl(fd, SPI_IOC_WR_MODE=0x40016b01, &mode)
spidev_module: __spidev_set_mode(): return -1
spidev_module: SpiDev_set_no_cs(): ret=-1
Traceback (most recent call last):
File "examples/bme280_simpletest.py", line 17, in <module>
bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)
File "/usr/local/lib/python3.5/dist-packages/adafruit_bme280.py", line 469, in __init__
super().__init__()
File "/usr/local/lib/python3.5/dist-packages/adafruit_bme280.py", line 120, in __init__
chip_id = self._read_byte(_BME280_REGISTER_CHIPID)
File "/usr/local/lib/python3.5/dist-packages/adafruit_bme280.py", line 428, in _read_byte
return self._read_register(register, 1)[0]
File "/usr/local/lib/python3.5/dist-packages/adafruit_bme280.py", line 474, in _read_register
spi.write(bytearray([register])) #pylint: disable=no-member
File "/usr/local/lib/python3.5/dist-packages/Adafruit_Blinka-1.2.9.dev23+g1d32b1f.d20190410-py3.5.egg/busio.py", line 129, in write
return self._spi.write(buf, start, end)
File "/usr/local/lib/python3.5/dist-packages/Adafruit_Blinka-1.2.9.dev23+g1d32b1f.d20190410-py3.5.egg/adafruit_blinka/microcontroller/generic_linux/spi.py", line 44, in write
self._spi.no_cs = True # this doesn't work but try anyways
OSError: [Errno 22] Invalid argument
The strace output shows that ioctl() call fails:
ioctl(4, SPI_IOC_WR_MODE, 0xbe81bb97) = -1 EINVAL (Invalid argument)
from adafruit_blinka.
pdp7
commented on July 21, 2024
How does Adafruit_CircuitPython_BME280 expect chip select (CS) to be handled?
https://github.com/adafruit/Adafruit_CircuitPython_BME280/blob/master/adafruit_bme280.py#L468
class Adafruit_BME280_SPI(Adafruit_BME280):
"""Driver for BME280 connected over SPI"""
def __init__(self, spi, cs, baudrate=100000):
import adafruit_bus_device.spi_device as spi_device
self._spi = spi_device.SPIDevice(spi, cs, baudrate=baudrate)
super().__init__()adafruit_bus_device handles setting the CS pin:
https://github.com/adafruit/Adafruit_CircuitPython_BusDevice/blob/master/adafruit_bus_device/spi_device.py#L85
The SPI implementation in Adafruit_Blinka does NOT handle CS
https://github.com/adafruit/Adafruit_Blinka/blob/master/src/adafruit_blinka/microcontroller/generic_linux/spi.py
def write(self, buf, start=0, end=None):
if not buf:
return
if end is None:
end = len(buf)
try:
self._spi.open(self._port, 0)
try:
self._spi.no_cs = True # this doesn't work but try anyways
except AttributeError:
pass
self._spi.max_speed_hz = self.baudrate
self._spi.mode = self.mode
self._spi.bits_per_word = self.bits
self._spi.writebytes([x for x in buf[start:end]])
self._spi.close()
except FileNotFoundError as not_found:
print("Could not open SPI device - check if SPI is enabled in kernel!")
raisefrom adafruit_blinka.
pdp7
commented on July 21, 2024
This line in adafruit_blinka/microcontroller/generic_linux/spi.py:
self._spi.no_cs = True # this doesn't work but try anywayscauses the error:
File "/usr/local/lib/python3.5/dist-packages/Adafruit_Blinka-1.2.9.dev23+g1d32b1f.d20190410-py3.5.egg/adafruit_blinka/microcontroller/generic_linux/spi.py", line 44, in write
self._spi.no_cs = True # this doesn't work but try anyways
OSError: [Errno 22] Invalid argument
debug output:
generic_linux/spi.py: return from self._spi.open(self._port, 0)
generic_linux/spi.py: try: self._spi.no_cs
spidev_module: SpiDev_set_no_cs(): self->mode=0x1
spidev_module: SpiDev_set_no_cs(): SPI_NO_CS=0x40
spidev_module: SpiDev_set_no_cs(): set SPI_NO_CS bit
spidev_module: SpiDev_set_no_cs(): tmp=0x41
spidev_module: SpiDev_set_no_cs(): call __spidev_set_mode()
spidev_module: __spidev_set_mode(): fd=4
spidev_module: __spidev_set_mode(): mode=0x41
spidev_module: __spidev_set_mode(): call ioctl(fd, SPI_IOC_WR_MODE=0x40016b01, &mode)
spidev_module: __spidev_set_mode(): return -1
spidev_module: SpiDev_set_no_cs(): ret=-1
What is happening in self._spi.no_cs = True?
It invokes this code in spidev_module.c:
{"no_cs", (getter)SpiDev_get_no_cs, (setter)SpiDev_set_no_cs,
"disable chip select\n"},which calls:
SpiDev_set_no_cs(SpiDevObject *self, PyObject *val, void *closure)which calls:
static int __spidev_set_mode( int fd, __u8 mode)this is where the ioctl() that fails is called:
if (ioctl(fd, SPI_IOC_WR_MODE, &mode) == -1) {
This ioctl() is trying to set the SPI mode with the NO_CS bit set.
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pdp7
commented on July 21, 2024
How does the Linux kernel handle SPI_NO_CS?
Here are the references to SPI_NO_CS in Linux kernel source code:
https://elixir.bootlin.com/linux/v4.19/ident/SPI_NO_CS
It is defined in:
https://elixir.bootlin.com/linux/v4.19/source/include/linux/spi/spi.h#L160
#define SPI_NO_CS 0x40 /* 1 dev/bus, no chipselect */The Raspberry Pi (BCM2835 processor) seems to support SPI_NO_CS:
https://elixir.bootlin.com/linux/v4.19/source/drivers/spi/spi-bcm2835.c#L79
#define BCM2835_SPI_MODE_BITS (SPI_CPOL | SPI_CPHA | SPI_CS_HIGH \
| SPI_NO_CS | SPI_3WIRE)from adafruit_blinka.
pdp7
commented on July 21, 2024
SPI driver for BeagleBone does not support for SPI_NO_CS
The BeagleBone has TI Sitara AM3358 SoC. The support in the Linux kernel is often referred to as OMAP given the previous TI SoC family.
SPI on the AM3358 is called McSPI and is implemented in:
https://elixir.bootlin.com/linux/v4.14/source/drivers/spi/spi-omap2-mcspi.c
The allowed mode bits are:
https://elixir.bootlin.com/linux/v4.14/source/drivers/spi/spi-omap2-mcspi.c#L1351
master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH;The allowed mode bits for the SPI controller (spi->controller->mode_bits) are checked in:
https://elixir.bootlin.com/linux/v4.19/source/drivers/spi/spi.c#L2787
int spi_setup(struct spi_device *spi)
{
/*snip*/
bad_bits = spi->mode & ~spi->controller->mode_bits;
ugly_bits = bad_bits &
(SPI_TX_DUAL | SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD);
if (ugly_bits) {
dev_warn(&spi->dev,
"setup: ignoring unsupported mode bits %x\n",
ugly_bits);
spi->mode &= ~ugly_bits;
bad_bits &= ~ugly_bits;
}
if (bad_bits) {
dev_err(&spi->dev, "setup: unsupported mode bits %x\n",
bad_bits);
return -EINVAL;
}In the case of the BeagleBone, the omap2-mcspi driver does not support SPI_NO_CS so spi_setup() returns -EINVAL which translates to -22. This is why Python has the exception: OSError: [Errno 22] Invalid argument
I recompiled the kernel on the BeagleBone with some print statements which confirms that setting SPI_NO_CS (0x40) causes bad_bits to be non-zero and spi_setup() to return -EINVAL:
[ 129.472021] DEBUG: spidev.c: SPI_IOC_WR_MODE
[ 129.476873] DEBUG: spidev.c: SPI_IOC_WR_MODE: save=0x1
[ 129.484114] DEBUG: spidev.c: SPI_IOC_WR_MODE: tmp=0x41
[ 129.490318] DEBUG: spidev.c: SPI_IOC_WR_MODE: SPI_MODE_MASK=0xfff
[ 129.497454] DEBUG: spidev.c: SPI_IOC_WR_MODE: ~SPI_MODE_MASK=0xfffff000
[ 129.505120] DEBUG: spidev.c: SPI_IOC_WR_MODE: (tmp&~SPI_MODE_MASK)=0x0
[ 129.512642] DEBUG: spi.c: spi_setup(): spi->mode=0x41
[ 129.518549] DEBUG: spi.c: spi_setup(): spi->controller->mode_bits=0x7
[ 129.526020] DEBUG: spi.c: spi_setup(): ~spi->controller->mode_bits=0xfffffff8
[ 129.534085] DEBUG: spi.c: spi_setup(): bad_bits=0x40
[ 129.539908] DEBUG: spi.c: spi_setup(): ugly_bits=0x0
[ 129.545715] DEBUG: spi.c: spi_setup(): unsupported mode bits, return -EINVAL
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ladyada
commented on July 21, 2024
hihi yeah so there are situations where you want to use the SPI bus w/o a CS pin (dotstars for example) so what we do is we have one 'dummy' CS pin that we always toggle but never connect to. Then we use any plain gpio pin for CS. this lets us have any CS pin, and any config of SPI, at the loss of a GPIO
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pdp7
commented on July 21, 2024
@ladyada thanks, yes, I can see why it is useful to decouple CS from the hardware SPI peripheral.
As a test, I just commented out all instances of self._spi.no_cs = True in src/adafruit_blinka/microcontroller/generic_linux/spi.py and the BME280 example runs OK on the BeagleBone:
debian@beaglebone:~/Adafruit_Blinka$ sudo python3 ~/Adafruit_CircuitPython_BME280/examples/bme280_simpletest.py 2>/dev/null |grep -v generic_linux |grep -v Adafruit_CircuitPython
Temperature: 23.7 C
Humidity: 39.7 %
Pressure: 1020.0 hPa
Altitude = -56.05 meters
This is because spidev no longer tries to set the SPI_NO_CS mode bit which is unsupported by the Linux driver (omap2_mcspi) for BeagleBone's SPI controller (AM3358 McSPI).
I think a work around maybe to add logic to skip setting no CS if AM3358 based board. I'll try that out and followup.
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ladyada
commented on July 21, 2024
please do a try-except
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ladyada
commented on July 21, 2024
fyi dont commit directly to this repo, have PRs only that i'll review. thanks :)
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pdp7
commented on July 21, 2024
OK, no problem. I will create PR when I have a working code.
For src/adafruit_blinka/microcontroller/generic_linux/spi.py,
I am thinking of replacing instances of:
try:
self._spi.no_cs = True # this doesn't work but try anyways
except AttributeError:
passwith a call to to a new method set_no_cs():
def set_no_cs(self):
print("generic_linux/spi.py: set_no_cs(): enter")
if detector.chip.AM33XX:
print("generic_linux/spi.py: set_no_cs(): detected AM33XX, SKIP setting no_cs")
else:
try:
print("generic_linux/spi.py: set_no_cs(): self._spi.no_cs = True")
self._spi.no_cs = True # this doesn't work but try anyways
except AttributeError:
passI just tested this out and the BME280 works OK on the BeagleBone. However, I think that calling detector.chip.AM33XX in set_no_cs() may be inefficient, so it might need to move to init().
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ladyada
commented on July 21, 2024
why not add an except for OSError?
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pdp7
commented on July 21, 2024
OSError can occur for any failed ioctl(). I think a better approach is avoid trying to set SPI_NO_CS mode bit when the chip is AM3358 (as this will always fail due to the Linux driver not supporting it).
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ladyada
commented on July 21, 2024
ok got it
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pdp7
commented on July 21, 2024
Tested OK with BME280 on PocketBeagle.
Make sure pins are configured for SPI0 plus P1.6 as GPIO for CS:
config-pin p1.6 gpio # CS
config-pin p1.8 spi_sclk # SPI0 CLK
config-pin p1.10 spi # SPI0 MISO
config-pin p1.12 spi # SPI0 MOSI
Adafruit_CircuitPython_BME280/examples/bme280_simpletest.py:
import board
import busio
import adafruit_bme280
import digitalio
spi = busio.SPI(board.SCK, board.MOSI, board.MISO)
bme_cs = digitalio.DigitalInOut(board.P1_6)
bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)
print("\nTemperature: %0.1f C" % bme280.temperature)debian@beaglebone:~$ python3 bme280_simpletest.py
Temperature: 22.0 C
system version info:
debian@beaglebone:~$ cat /etc/dogtag
BeagleBoard.org Debian Image 2019-03-03
debian@beaglebone:~$ uname -r
4.14.78-bone17
debian@beaglebone:~$ cat /etc/debian_version
9.8
debian@beaglebone:~$ ls -ltar /dev/spidev*
crw-rw---- 1 root spi 153, 0 Apr 12 17:41 /dev/spidev0.0
crw-rw---- 1 root spi 153, 1 Apr 12 17:42 /dev/spidev1.0
crw-rw---- 1 root spi 153, 2 Apr 12 17:42 /dev/spidev1.1
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