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Re: Serial Latency Issues, Baud Rate Affects Buffering




----- Original Message -----
From: "Eric Sorton" <esorton@xxxxxxx.org>
To: "Mikael Starvik" <starvik@xxxxxxx.com>; "Johan Adolfsson"
<johana@xxxxxxx.com>
Sent: den 12 januari 2004 14:36
Subject: Re: Serial Latency Issues, Baud Rate Affects Buffering
..

> All of these options expect the serial port to stop transmitting data for
a
> period of time before flushing the DMA buffer.  Our stream transmits data
> almost continuously, thus the DMA buffer is never flushed UNTIL it is full
at
> 256 bytes, which at 4800 baud, is over 1/2 a second.  Note, I still need
to
> try the code modification mentioned in a previous message.
>
> The new serial driver provides an option for disabling DMA.  What are the
> repercussions of disabling DMA?

At low baudrates, it shouldn't really matter. At 115200 you might loose
a character now for and then though and above 115200 it's rather useless.

> Will this help reduce the latency in the
> read?

Yes, it should behave more like normal PC, the incoming data is put in
the flip buffer and pushed to the tty layer at each character interrupt.

> Thank you for all of your help, it is greatly appreciated,
>
> Eric

/Johan