On Fri, 21 May 2021 09:39:34 -0700, in gmane.comp.hardware.beagleboard.user
"John Dammeyer" <[email protected]> wrote:
>static const char *device = "/dev/spidev1.0";
> fd = open(device, O_RDWR);
> if (fd < 0)
> pabort("can't open device");
>
>One of two things happen. Either It opens the SPI bus which includes
>everything that config-pin does or it fails because config-pin wasn't done.
Hypothesis: The "device" (driver) is loaded -- but the pin-mux does not
have the pins connected to the internal port(s) used by the driver... So
the driver is basically dumping output into the "bit-bucket".
It can't really take control -- since the same pins are used by I2C
mode, if opening the "device" did the pin-mux one could really mess up data
transfers (open "I2C" start transfer, then open SPI using the same pins).
>> >Oh and none of this explains why the ioctl regardless of C or Pascal
>> >
>can't handle more than 4096 data bytes while the Python code can when sending
>a large bitmap to the SPI port.
>...
>> debian@beaglebone:~$ cat /sys/module/spidev/parameters/bufsiz
>> 4096
>> debian@beaglebone:~$
>
>How did you know to look at this file to determine the SPI buf size?
https://www.kernel.org/doc/Documentation/spi/spidev
"""
- There's a limit on the number of bytes each I/O request can transfer
to the SPI device. It defaults to one page, but that can be changed
using a module parameter.
- Because SPI has no low-level transfer acknowledgement, you usually
won't see any I/O errors when talking to a non-existent device.
"""
along with the source for the Python spidev module, which explicitly
mentions that parameter... Though just doing
sudo find / -iname "spidev"
and exploring what each result contains (or to bypass one layer)
debian@beaglebone:~$ ls -R `sudo find / -iname "spidev"`
/sys/bus/spi/drivers/spidev:
bind module spi0.0 spi0.1 spi1.0 spi1.1 uevent unbind
/sys/class/spidev:
spidev0.0 spidev0.1 spidev1.0 spidev1.1
/sys/devices/platform/ocp/48030000.spi/spi_master/spi0/spi0.0/spidev:
spidev0.0
/sys/devices/platform/ocp/48030000.spi/spi_master/spi0/spi0.0/spidev/spidev0.0:
dev device power subsystem uevent
/sys/devices/platform/ocp/48030000.spi/spi_master/spi0/spi0.0/spidev/spidev0.0/power:
async runtime_active_kids runtime_status
autosuspend_delay_ms runtime_active_time runtime_suspended_time
control runtime_enabled runtime_usage
/sys/devices/platform/ocp/48030000.spi/spi_master/spi0/spi0.1/spidev:
spidev0.1
/sys/devices/platform/ocp/48030000.spi/spi_master/spi0/spi0.1/spidev/spidev0.1:
dev device power subsystem uevent
/sys/devices/platform/ocp/48030000.spi/spi_master/spi0/spi0.1/spidev/spidev0.1/power:
async runtime_active_kids runtime_status
autosuspend_delay_ms runtime_active_time runtime_suspended_time
control runtime_enabled runtime_usage
/sys/devices/platform/ocp/481a0000.spi/spi_master/spi1/spi1.0/spidev:
spidev1.0
/sys/devices/platform/ocp/481a0000.spi/spi_master/spi1/spi1.0/spidev/spidev1.0:
dev device power subsystem uevent
/sys/devices/platform/ocp/481a0000.spi/spi_master/spi1/spi1.0/spidev/spidev1.0/power:
async runtime_active_kids runtime_status
autosuspend_delay_ms runtime_active_time runtime_suspended_time
control runtime_enabled runtime_usage
/sys/devices/platform/ocp/481a0000.spi/spi_master/spi1/spi1.1/spidev:
spidev1.1
/sys/devices/platform/ocp/481a0000.spi/spi_master/spi1/spi1.1/spidev/spidev1.1:
dev device power subsystem uevent
/sys/devices/platform/ocp/481a0000.spi/spi_master/spi1/spi1.1/spidev/spidev1.1/power:
async runtime_active_kids runtime_status
autosuspend_delay_ms runtime_active_time runtime_suspended_time
control runtime_enabled runtime_usage
/sys/module/spidev:
coresize holders initstate parameters sections uevent
drivers initsize notes refcnt taint
/sys/module/spidev/drivers:
spi:spidev
/sys/module/spidev/holders:
/sys/module/spidev/notes:
/sys/module/spidev/parameters: <<<<<
bufsiz
<<<<<
/sys/module/spidev/sections:
__jump_table __mcount_loc __param __verbose
debian@beaglebone:~$
--
Dennis L Bieber
--
For more options, visit http://beagleboard.org/discuss
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