Serial interface sends one bit upon open()

[Norbert Danneberg]

I'm trying to set up a serial communication between the RPI and an FPGA. However, there is an issue when using the standard C library open() to init the serial interface: I'm using a scope to monitor what is sent and received via the RX and TX lines. A call to open causes the TX line of the RPI to go low for the length of one bit. I do not see this behavior with other computers/linux PCs. The point is, the FPGA assumes a valid transmission, since he thinks it's a start bit, but it's not.

I checked with minicom installed on the RPI. Same thing. Starting minicom causes the TX line sending one bit. Once minicom has started, the communication runs as expected and all bytes have the correct frame size. Is there any way to suppress the TX line going low upon the open call to init the serial communication? A smart guy at stackoverflow suggested:

http://stackoverflow.com/questions/14579974/init-a-serial-communication-with-c-library-open-causes-tx-to-send-one-bit-on-r

Thanks
N.

[peter green (plugwash)]

This sounds like a kernel issue, can you take it up with the raspberry pi kernel developers at https://github.com/raspberrypi/linux/issues

[Norbert Danneberg (7nfo)]

Thanks.

I will open an issue.

Cheers

N.

Am 02.02.2013 um 00:02 schrieb peter green:

> This sounds like a kernel issue, can you take it up with the raspberry
> pi kernel developers at https://github.com/raspberrypi/linux/issues
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1109099
>
> Title:
> Serial interface sends one bit upon open()
>
> Status in Raspbian - Debian Hard Float for Raspberry Pi:
> New
>
> Bug description:
> I'm trying to set up a serial communication between the RPI and an
> FPGA. However, there is an issue when using the standard C library
> open() to init the serial interface: I'm using a scope to monitor what
> is sent and received via the RX and TX lines. A call to open causes
> the TX line of the RPI to go low for the length of one bit. I do not
> see this behavior with other computers/linux PCs. The point is, the
> FPGA assumes a valid transmission, since he thinks it's a start bit,
> but it's not.
>
> I checked with minicom installed on the RPI. Same thing. Starting
> minicom causes the TX line sending one bit. Once minicom has started,
> the communication runs as expected and all bytes have the correct
> frame size. Is there any way to suppress the TX line going low upon
> the open call to init the serial communication? A smart guy at
> stackoverflow suggested:
>
> http://stackoverflow.com/questions/14579974/init-a-serial-
> communication-with-c-library-open-causes-tx-to-send-one-bit-on-r
>
> Thanks
> N.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/raspbian/+bug/1109099/+subscriptions

[James Stevenson (ja7es)]

Marked as invalid as issue has probably been raised and fixed on the kernel