Re: [avrdude-dev] avr910 speed-testing/tuning

[Jan-Hinnerk Reichert]

On Wednesday 10 December 2003 13:04, Joerg Wunsch wrote:
> As Jan-Hinnerk Reichert wrote:
> > The explanation is simple: The PC's UART (TL16C550) waits 4
> > byte-lenght before it requests an interrupt, because the
> > FIFO-threshold of 8 is not reached. The remaining 0.4
> > byte-lengths are SPI-transfer in the programmer and
> > system/program-overhead.
>
> The designers of UUCP already knew that request-response protocols
> suck.  The designers of AVR910 apparently didn't have this 20-year
> old knowledge...

Ancient knowledge often gets lost ;-)

> > However, there is no simple solution here, since the
> > FIFO-threshold is hardcoded in the kernel.
>
> For FreeBSD, the FIFO can be disabled per device at boot-time,
> using device flag 0x02.  For FreeBSD <= 4, this is a kernel
> comfiguration parameter but one that can be overridden by the
> loader at boot-time. For FreeBSD 5, this is always configured in
> /boot/device.hints, no recompilation required at all.

What do you mean by disable? Don't rely on it or disable it?

Under Linux you can disable the FIFO with "setserial" by selecting a 
"16450"-UART. However, this really disables the FIFO in hardware, so 
you get lost bytes at higher baudrates ;-(

/Jan-Hinnerk