Re: TTY_FLIPBUF_SIZE too low causing dataloss on too fast serial lines?

Bjorn Wesen (bjorn@sparta.lu.se)
Fri, 28 May 1999 19:49:30 +0200 (MET DST)

On Wed, 26 May 1999, Theodore Y. Ts'o wrote:
> I simply haven't see much demand or practical application for high-speed
> serial transfers. It's restricted to short distance unless you use
> *very* expensive cables, and you can get better performance more cheaply
> simply by using Ethernet instead. 10 Megabit ethernet cards are dirt
> cheap, and Cat 5 UTP cables are much, much cheaper than high-quality
> serial cables, and you can run them for a much greater distance without
> worrying about noise or signal degredation problems.

The one exception is embedded systems (to which Linux is beginning to
catch on).

In our HW, we have 6.25 Mbaud serial ports. They can be used to talk to
other stuff on the board, or with other similar CPU's. They can also talk
with the lower standard speeds, like 1.8 Mbaud and below.

So in our Linux driver, I'm using the serial port DMA to send incoming
data into a static buffer which is, when the DMA is finished, copied into
the flip buffer and the flip call is made. On the sending side, DMA is
started directly from the xbuf.

Now, I know this is a waste of buffers and copyings and power, but it
works for now. However maybe I can optimize it by starting DMA directly
into the flipbuf or bypass the flipbuf - mayby you have a hint (I'll check
that Rocketport driver btw).

brgds
Bjorn

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