I’ve started to explore a topic to turn VIM3/VIM3L into powerful signal processor as seems that SBC and Amlogic chip is much better suited for that rather then Raspberry PI4 due onboard NPU and built-in audio-codec.
And it would be much appreciated if you can give some answers and guidance on that long way.
From my perspective if I could make NPU to run the same - it would be really great.
But the target is a bit difficult to reach as there are some steps needs to be taken
1/ Adopt Xenomai and Elk audio project (realtime linux microkernel ) to Amlogic chip
2/ Adapt Amlogic audio drivers to RTDM (realtime driver model) in Xenomai taking other as example - https://github.com/elk-audio/rpi-rtdm-audio-driver
3/ Attach some ADC/DAC hardware to I2S bus.
and etc…
So to just explore possibilities without going into much HW changes - I’m planning to tryout SPDIF IN/OUT ports on VIM3/L SBC and luckily all that available on 40 pin header
SPDIF out is already there, but for SPDIF I wanted to change PWM_F pin into SPDIF IN - could you please let me know what needs to be changed (u-boot, dts, smth else) to change this pin into SPDIF mode ?
Is it possible to use the SPDIF out GPIO pins with linux mainline kernel also (with VIM3L)?
With 4.9 linux kernel built with Fenix it works fine, but with mainline kernel only sound via hdmi is possible (no sound device with output to spdif is configured). Can this be achived by modifying and compiling the device tree source for the VIM3L board or is there some kind of hardware support still missing in mainline linux?
Hi @hyphop, thank you for your support. I tried your suggestions, but i have sound over gpio-spdif-pins only with Krescue Audio Tests. Here is what else i have tried:
burn the image you linked to sdcard: only sound via hdmi
build generic image with fenix, burn to sdcard: only sound via hdmi
build vim3l image with fenix (mainline kernel, mainline u-boot), burn to sdcard: only sound via hdmi
download linux-mainline 5.16-rc1, patched with patches you linked, configured boot partition of sdcard to use new kernel, new initrd and new dtb.img, which booted successfully, but again: only sound via hdmi
I kindly ask if you have any hint, why sound via spdif-pins is only working in krescue audio tests?