topic Re: I.mx28 9 bit data UART linux drivers in i.MX Processors

I.mx28 9 bit data UART linux drivers

desmondcorreia — Tue, 02 Aug 2016 20:53:14 GMT

Hi,

Has anyone implemented a 9 bit data UART driver under linux for the I.mx28. I have been reviewing the "MCIMX28RM" document and as far as I see it's not possible to read the 9bit from the UART register since the hardware just tells you the status of the parity bit.

Does anyone have any idea how I could do this. I need to know what the 9bit is since I am trying to interface the I.mx28 with a UART that uses 9bit data for UART

Thanks

Re: I.mx28 9 bit data UART linux drivers

igorpadykov — Wed, 03 Aug 2016 06:34:20 GMT

Hi Desmond

you are right i.MX28 uart hardware does not support 9 data bits.

Best regards

igor

Re: I.mx28 9 bit data UART linux drivers

lategoodbye — Wed, 03 Aug 2016 20:42:55 GMT

Hi Desmond,

in case you don't need 9 bit + parity it's possible to emulate bit 9 with parity (like here: https://viereck.ch/linux-mark-space-parity/ ).

Based on this similiar patch: https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=bb70002cb7430252c6c8e3b19ad66957f253e667

i attached one for mxs-auart from Mainline Linux 4.5. I only compile tested this patch.

Re: I.mx28 9 bit data UART linux drivers

desmondcorreia — Wed, 03 Aug 2016 21:00:45 GMT

Hi Stefan,

Thanks for response. I don't want to write 9bit data I need to read it. I came up with a scenario to derive the 9th bit. See below and give me your thoughts.

Imx28 is setup to use even parity checking
We calculate the parity error on 8 bits using even parity checking and always using the 9th bit as 0
We take our parity error flag XOR with imx28 parity error flag
The result is the 9th bit

Re: I.mx28 9 bit data UART linux drivers

lategoodbye — Thu, 04 Aug 2016 16:40:36 GMT

Hi Desmond,

i think your thoughts should be okay. I think the tricky part is to detect the parity errors with termios. Maybe the flag PARMRK should do the trick.