On Fri, May 21, 2021 at 11:40 AM John Dammeyer <jo...@autoartisans.com> wrote: > > Thanks Dennis, > > > > -----Original Message----- > > From: beagleboard@googlegroups.com [mailto:beagleboard@googlegroups.com] On > > Behalf Of Dennis Lee Bieber > > "John Dammeyer" <johnd-5o6ditlojsohvde0pjs...@public.gmane.org> 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. > > My posting from > Fri 14/05/2021 > RE: [beagleboard] Configure CAN0 with buildroot > > talks about using config-pin for CAN bus. I spent so much time a number of > years ago learning about SLOTs and spending time even writing my own DTS for > a proto board that has a 1-wire sensor. The Logic Supply CAN cape dts was > also used. > > I can't seem to completely unlearn (if that's the right term) and now still > get very confused as to what to use and when. > > So I guess I should have remembered that on the 14th of May I did use > config-pin for CAN so it must also be needed for SPI. > > > > > > 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 > > I've done that with the pins. But again my incorrect assumption was that the > OS was intelligent enough that if I do: > > 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. > In fact I believe that until the config-pin operations on the SPI pins is > done that the /dev/spidev1.0 shouldn't exist. That they are there is > incorrect information. > > But this is 'human factors engineering" which the Beagle (Linux?) lacks in a > big way. > > > > >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? > > I see that it's a read only file. > debian@ebb:~$ ls -al /sys/module/spidev/parameters/bufsiz > -r--r--r-- 1 root gpio 4096 May 20 16:45 > /sys/module/spidev/parameters/bufsiz > > The code I'm adapting from a 128x128 display sends out a 512x512 lenna.jpg > compressed into a smaller window. Even so any sort of bit map object that is > 128x128x16 for example is 32K in size. So no matter what sort of canvas I > draw on inside the application, to render it out to an SPI display still > requires 9 blocks of 4096 bytes. > > I'll look into that. Really don't want to write in Python. > > > 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} > > I was going to suggest that the BBB is now an out of date product but > https://www.digikey.ca/en/products/detail/beagleboard-by-seeed-studio/102110420/12719590 > shows over 4000 in stock. So maybe not?
The am335x based BBB is going to be around for a long time to come... Regards, -- Robert Nelson https://rcn-ee.com/ -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAOCHtYiEkosdy88FSb2aYDpwwOoLRjOpCPbN8wOi%3DV-AZ8oj4A%40mail.gmail.com.
