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Re: [avrdude-dev] avr910 speed-testing/tuning
From: |
Jan-Hinnerk Reichert |
Subject: |
Re: [avrdude-dev] avr910 speed-testing/tuning |
Date: |
Wed, 10 Dec 2003 13:23:42 +0100 |
User-agent: |
KMail/1.5.1 |
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
Re: [avrdude-dev] avr910 speed-testing/tuning, E. Weddington, 2003/12/10