Subject: Re: [PATCH 2/2] tty: serial: fsl_lpuart: writing a 1 and then a 0 to
trigger a break character
Hi,
Am 2022-07-15 04:59, schrieb Sherry Sun:
> According to the lpuart reference manual, need to writing a 1 and then
> a
> 0 to the UARTCTRL_SBK field queues a break character in the transmit
> data stream. Only writing a 1 cannot trigger the break character, so
> fix it.
I don't think this is correct. The tty core will already call this:
.break_ctl(port, 1)
usleep()
.break_ctl(port, 0)
So you'll have your 1->0 transition.
My RM from the LS1028A says the following:
| Writing a 1 and then a 0 to SBK queues a break character in the
| transmit data stream. Additional break characters of 10 to 13, or 13
| to 16 if LPUART_STATBRK13] is set, bit times of logic 0 are queued as
| long as SBK is set. Depending on the timing of the set and clear of
| SBK relative to the information currently being transmitted, a second
| break character may be queued before software clears SBK.
To me it seems that setting the SBK bit just pulls the TX line low and releasing
it will return to normal transmitter mode.
Hi Michael,
Actually set break_ctl(tty, -1) then break_ctl(tty, 0) is only done in
the send_break() function.
If we call TIOCSBRK from user space, it will only set break_ctl(tty,
-1) without break_ctl(tty, 0).
And from the definition of .break_ctl(port,ctl), the callback is used
to Control the transmission of a break
signal(Documentation/driver-api/serial/driver.rst), if ctl is nonzero,
it should queues a break character. I don't think it is reasonable to
call break_ctl() twice in order to send one break signal.
Also I have tried other uart IP, such as drivers/tty/serial/imx.c, it
also queues a break character if we call break_ctl() once. So I
believe the break_ctl() in lpuart driver should be fixed.