On Thu, 20 May 2021 19:19:08 -0700, in gmane.comp.hardware.beagleboard.user
"John Dammeyer" <[email protected]> wrote:
>The sad thing is that Derek Molloy's book, only in passing refers to enabling
>the SPI port, and the book, in trying to also deal with the pocket beagle pins
>leaves out things where repetition is actually beneficial. Maybe somewhere it
>says that you have to use config-pin to set up SPI. I missed it. I think in
>Chapter 8 page 363 needs a bit of work.
One: you have to look at the default pin-mux tables -- the default for
many is as GPIO.
Two: config-pin is discussed in chapter 6 (which also has a
hard-to-read version of the tables). It doesn't mention SPI explicitly, but
does mention that the tool is used in later chapters.
debian@beaglebone:~$
/opt/source/bb.org-overlays/tools/beaglebone-universal-io/config-pin -i
p9_18
Pin name: P9_18
Function if no cape loaded: gpio
Function if cape loaded: default gpio gpio_pu gpio_pd gpio_input spi i2c
pwm pru_uart
Function information: gpio0_4 default gpio0_4 gpio0_4 gpio0_4 gpio0_4
spi0_d1 i2c1_sda ehrpwm0_tripzone_input pru_uart
Kernel GPIO id: 4
PRU GPIO id: 36
debian@beaglebone:~$
>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. Nor why, according to this web site
debian@beaglebone:~$ cat /sys/module/spidev/parameters/bufsiz
4096
debian@beaglebone:~$
https://pypi.org/project/spidev/
"""
writebytes2(list of values)
Similar to writebytes but accepts arbitrary large lists. If list size
exceeds buffer size (which is read from
/sys/module/spidev/parameters/bufsiz), data will be split into smaller
chunks and sent in multiple operations.
"""
>https://learn.adafruit.com/setting-up-io-python-library-on-beaglebone-black/spi
>nothing is said about config-pin operations so the python library must do this
>automatically?
A lot of that is a bit out-of-date -- references to kernel 3.8! Though
I do have to admit I can't find where in Adafruit_BBIO it might do that
set-up -- it doesn't seem to be done in the above spidev Python interface,
which is used by (now deprecated in favor of blinka/circuitpython)
Adafruit_BBIO... And I can't find a config change in blinka or
Adafruit_PureIO. {PureIO may not invoke the above spidev module, so how
/it/ handles large blocks is unknown}
--
Dennis L Bieber
--
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