14:27 <Duality> hey

14:29 <Duality> I am working with an am335x and want to read some serial rs485 data the first byte I receive has the mark set (high parity bit always) and three following space (low parity bit always) but now is my question is there any way to tell linux to not substitute parity errors with 0x00 and just give the value anyway

14:29 <Duality> I tried several things with termios and IGNPAR + setting parity space

14:30 <Duality> but I am really scratching my head lol I have been going through so many permutations of settings but nothing works.

14:31 <Duality> I can see when I ONLY set space parity I get the 3 data bytes just fine first one is always 0x00 but when I set the mark parity I get the first byte just fine but the three following are always 0x00

15:16 <zmatt> Duality: so basically you just want 9 data bits :P

15:19 <zmatt> what you want is possible in theory at the hw level (although it precludes using dma), though I'm pretty sure not using the linux serial driver... you could use uio instead (which gives userspace direct access to a peripheral and its interrupts) or have pru handle reception and forward the messages to userspace e.g. via a ringbuffer

15:42 <zmatt> do you also need to transmit or only receive?

15:47 <zmatt> an uart is not super difficult to work with, though it's kinda crufty due to being covered in layers of backwards compatibility with ancient uarts, which in particular makes initialization kinda messy (iirc the AM335x TRM actually gets it wrong)

15:53 <zmatt> of course if you're doing half-duplex rs485 transmit and receive then you'll probably want to use pru rather than uio to get reliable timing