Unexpected behavior of SPI on BeagleBone Black

toshi

Hi. I recently inherited an old BBB-Bela setup and I encountered an issue while running the SPI example.
According to other posts on the forum, the soft-SPI from BB-BELA-CTAG-SPI-00A0 uses pins on the P8 header. However, I see signals on P9_29, P9_30 and P9_31 (the BBB SPI1 pins). The signal on P9_31 is clearly a clock signal.
But there is no SS signal on P9_28.

Info on my setup:
Bela Rev B2, 09/17
Bela Image v0.3.8h, updated with Bela-master.zip via the IDE.

I tried loading cape-universalh-00A0, but it causes gpio conflicts during boot and /dev/spidev3.* to disappear.
Also tried the v0.5.0alpha2 image, but same issue with SPI signals not going to the P8 pins.

My motivation for getting SPI to work is so I can hook up an ILI9488 to display waveform/harmonic analysis.
I've done similar projects on RPI and Libre S905x so I must be misunderstanding something fundamental on the Bela platform...

-Toshi

giuliomoro

v0.3.8h is the latest stable image.

SPI to the cape's AD5688 and AD7699 (which provide the analog inputs and outputs) is on the P9 pins you mentioned (using the spi0 peripheral). The soft-SPI on the P8 pins is unused unless you have a CTAG cape connected, which doesn't seem to be the case.

The two channels of soft-spi will be /dev/spidev3.0 and /dev/spidev3.1 with the default overlays. Keep in mind the soft SPI will be pretty slow, CPU intensive and dependent on system load, as it's bitbanged. If you don't need the analog inputs and outputs, then disable them in the IDE and you can use the spi0 peripheral on the pins on P9 for your display. Note that spi0 is not declared to Linux via the device tree and therefore it doesn't show up on /dev/spidev*, although the pinmuxing for those pins is correctly set. So you'd need to load an appropriate overlay that at the very minimum sets status = "okay" on the spi0 node if you want to use it via Linux.

toshi

Thanks for the quick response and clarification.
As I need the analog inputs for the signal analysis, I won't be able to use the native linux SPI.
The soft-SPI probably isn't fast enough for a 320x480 display so I need to figure out an alternative - Bela web UI or a separate arduino board.
Thanks!!