Newbie question: setting baudrate / managing FIFO.

Newbie question: setting baudrate / managing FIFO.

[Andrei Warkentin]

Hi,

I looked about the archives, but maybe I skipped something... When I
am handling set_termios, what assumptions can I make regarding the
TX/RX state? I didn't take a look at all the serial drivers, but the
ones I did look did not bother flushing FIFOs and ensuring nothing can
be present in the TX FIFO while updating LCR and divisors. Should I do
the equivalent of stop_tx inside set_termios? Is that already ensured?
The hardware I am looking at needs to have FIFO cleared after setting
baud rate, and I was getting concerned over potential data loss
scenarios...

Thanks,
A

Re: Newbie question: setting baudrate / managing FIFO.

[Andrei Warkentin]

On Wed, Feb 16, 2011 at 4:51 AM, Andrei Warkentin <andreiw@motorola.com> wrote:
> Hi,
>
> I looked about the archives, but maybe I skipped something... When I
> am handling set_termios, what assumptions can I make regarding the
> TX/RX state? I didn't take a look at all the serial drivers, but the
> ones I did look did not bother flushing FIFOs and ensuring nothing can
> be present in the TX FIFO while updating LCR and divisors. Should I do
> the equivalent of stop_tx inside set_termios? Is that already ensured?
> The hardware I am looking at needs to have FIFO cleared after setting
> baud rate, and I was getting concerned over potential data loss
> scenarios...
>
> Thanks,
> A
>

I realize there are different versions of the TCSET - TCSETS,
TCSETF... i.e. if you wanted to flush the buffer you'd ask for it. So
it should be ok to just clear the FIFO and destroy anything in them,
right? Or should I still flush the FIFOs after disabling flow control
if it was on? After all you could have gotten data after you called
set_termios.

Thanks,
A

Re: Newbie question: setting baudrate / managing FIFO.

[Andrei Warkentin]

On Wed, Feb 16, 2011 at 1:07 PM, Andrei Warkentin <andreiw@motorola.com> wrote:
> On Wed, Feb 16, 2011 at 4:51 AM, Andrei Warkentin <andreiw@motorola.com> wrote:
>> Hi,
>>
>> I looked about the archives, but maybe I skipped something... When I
>> am handling set_termios, what assumptions can I make regarding the
>> TX/RX state? I didn't take a look at all the serial drivers, but the
>> ones I did look did not bother flushing FIFOs and ensuring nothing can
>> be present in the TX FIFO while updating LCR and divisors. Should I do
>> the equivalent of stop_tx inside set_termios? Is that already ensured?
>> The hardware I am looking at needs to have FIFO cleared after setting
>> baud rate, and I was getting concerned over potential data loss
>> scenarios...
>>
>> Thanks,
>> A
>>
>
> I realize there are different versions of the TCSET - TCSETS,
> TCSETF... i.e. if you wanted to flush the buffer you'd ask for it. So
> it should be ok to just clear the FIFO and destroy anything in them,
> right? Or should I still flush the FIFOs after disabling flow control
> if it was on? After all you could have gotten data after you called
> set_termios.
>
> Thanks,
> A
>

Anyone :)?

Re: Newbie question: setting baudrate / managing FIFO.

[Grant Edwards]

On 2011-02-16, Andrei Warkentin <andreiw@motorola.com> wrote:

> I looked about the archives, but maybe I skipped something... When I
> am handling set_termios, what assumptions can I make regarding the
> TX/RX state? I didn't take a look at all the serial drivers, but the
> ones I did look did not bother flushing FIFOs and ensuring nothing can
> be present in the TX FIFO while updating LCR and divisors. Should I do
> the equivalent of stop_tx inside set_termios? Is that already ensured?
> The hardware I am looking at needs to have FIFO cleared after setting
> baud rate, and I was getting concerned over potential data loss
> scenarios...

Somebody who changes baud rate while transmitting is going to lose
data no matter what you choose to do.

So, I wouldn't worry about it.  Change the baud rate when the ioctl()
tells you to, and if you have to clear the FIFO as part of that
operation then do so.

-- 
Grant Edwards               grant.b.edwards        Yow! I just went below the
                                  at               poverty line!
                              gmail.com