9 bit protocol on UART in embedded Linux

Question

I am trying to force a 9-bit protocol on a UART in embedded Linux. Currently I am testing this out on the am335x_evm board. I am planning on doing this using stick parity. Ideally I was hoping I would not need to actually modify any of the code for the omap-serial.c driver.

The reason for the 9-bit protocol is to support some legacy hardware that uses it. The parity bit needs to be 1 for the address portion of the message, 0 for the data portion, then 1 again for the termination byte.

I was planning on having a process running in user space that would interface with the UART through standard system calls (open, write, read, ioctl, tcsetattr, etc). I would configure the UART to enable parity and set the stick parity. I would then set the parity to even and call write() to send out my address data. I would then set the parity to 0 and send out the data. My concern is if I change the parity from 1 to 0, when does that take affect? If the UART is not done sending all the address data, will the change in parity apply to any unsent data?

Answer 1

Proper way is to set cs9 on your serial port (and possibly no parity), provided that hardware and driver support this.

I'll search for a link for you...

Answer 2

Ended up writing my own 9-bit uart driver. Was the easiest and most efficient solution.