Loading device tree overlay to use config-pin

Laimonade

Hey all,

I'm trying to load the device tree overlay /lib/firmware/cape-universala-00A0.dtbo to be able to use SPI on Bela.
I'm disabling the analog I/O's from the IDE and following the wiki https://learn.bela.io/using-bela/technical-explainers/device-tree-overlays/ to do so but so far no luck.
Adding the above .dtbo in uEnv.txt prevents Bela from booting after restart.

Am I supposed to remove the other overlay addr already contained in uEnv.txt?

Any help would be much appreciated.

Thank you,
Leo

giuliomoro

see this https://forum.bela.io/d/2589-gpio-pin-number-confusion/10

you need an updated Bela dtbo and cape-universalh

Laimonade

giuliomoro Cheers Giulio! Just tried it and it does not seem to work unfortunately.
Step that I have tried:
- Cloning branch on Bela
- cd bb.org-overlays & make all install
- load the cape-universalh by adding its address as such

uboot_overlay_addr1=/lib/firmware/cape-universalh-00A0.dtbo
uboot_overlay_addr2=/lib/firmware/BB-BELA-00A1.dtbo

Bela now boots up (however takes a lot longer) but I still cannot access config-pin:

P9_18 pinmux file not found!
Pin has no cape: P9_18

giuliomoro

Btw, sometimes if it looks like the board is not booting it could be because the change in the dtb makes it so that the button results as pressed and triggers a shutdown of the board shortly after boot.
To avoid this when working with dtbs, disable it by running systemctl disable bela_button before you start messing around with overlays (can be enabled later with systemctl enable bela_button).

giuliomoro

P9.18 is already used for SPI by the onboard ADC and DAC, so we disable config-pin for it (but it's already set to SPI!). Unfortunately there is no other hw SPI bus available on the BBB headers, so if you want to use an SPI device, you have two options: either disable the analog I/O of Bela and use its pins, or use soft SPI. Soft SPI is much slower bandwidth and higher CPU consumption than hw SPI, but it could still be good for some low-bandwidth applications.

To use it, ensure you load /lib/firmware/BB-BELA-CTAG-SPI-00A0.dtbo (and no cape-universal). This makes the following pins available:

                    0x0DC 0x37 /* spi_sclk,     MODE7 | INPUT_PULLUP | SPI_SCLK P8_32 */
                    0x028 0x37 /* spi_miso,     MODE7 | INPUT_PULLUP | SPI_MISO P8_14 */
                    0x0D4 0x17 /* spi_mosi,     MODE7 | OUTPUT_PULLUP | SPI_MOSI P8_33 */
                    0x02C 0x17 /* spi_cs0,      MODE7 | OUTPUT_PULLUP | SPI_CS0 P8_17 */
                    0x0D8 0x17 /* spi_cs1,      MODE7 | OUTPUT_PULLUP | SPI_CS1 P8_31 */

Laimonade

giuliomoro Right, so I had read that there was no spare SPI bus on the normal Bela so I did disable analog I/O as I don't need them. But what you're saying is that disabling analog I/O's automatically re-assign the SPI bus to those pins so there's no need to use config-pin to set up each SPI0 pins?

Also sorry I can't seem to find it but, but do you know where I could find which analog pins corresponds to which P9 pins? (e.g.: A1 -> P9.X).

giuliomoro

Laimonade Also sorry I can't seem to find it but, but do you know where I could find which analog pins corresponds to which P9 pins? (e.g.: A1 -> P9.X).

See the highlighted pin functions here

Laimonade ut what you're saying is that disabling analog I/O's automatically re-assign the SPI bus to those pins so there's no need to use config-pin to set up each SPI0 pins?

Kindof. The pins are hard-coded to work as SPI. If Bela doesn't use them, they remain available for you to use them.

Laimonade

giuliomoro Perfect thank you for the help 🙂 I think I have it figured out!