[U-Boot] [PATCH v2] NS16550: buffer reads

[Wolfgang Denk]

Dear Simon Glass,

In message <CAPnjgZ37O2tr1kY5f-uv1zymGBdMLbyEhm6y-=rfENJ62jnREg at mail.gmail.com> you wrote:
> 
> > How about using the time-honored flow-control mechanism? If the serial port
> > supports hardware CTS and RTS signals, you can use them to sync with the
> > sender. If not, you can send XOFF and XON to respectively ask the sender to
> > pause and resume sending. Of course, the sender must support hardware or
> > software flow control.
>
> It is common to have just a 2-wire UART for the console. Perhaps this
> is unfortunate.

Indeed that's a pretty common configuration - but soft-flow would
still work fine.

> Are you suggesting that U-Boot should send XOFF sometimes, or does it
> support this already? (I haven't seen it). When would U-Boot send
> XOFF? Perhaps it could send XOFF at the end of each line that it
> receives. Then XON when it starts reading the next line or maybe when
> it runs out of characters and wants more.

It should be sufficient to send XOFF when receiving a '\n' character
(and storing that state) and XON when expecting inout (if state says
XOFF had been sent before).

> Most terminal problems will support software flow control. But are you
> sure this is better?

Definitely.  for example, because it is hardware independent and will
work on all architectures, all SoCs, all UARTs.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"We don't care.  We don't have to.  We're the Phone Company."