Subject: Re: Hope for winmodem support?
To: Steven Grunza <email@example.com>
From: None <Chris.Smith@raytheon.co.uk>
Date: 02/15/2001 15:22:53
> It would seem, in theory, that a "winmodem" type of device
> could provide better performance since it's data path into
> the system is across a parallel bus and not through the
> serial port. Also, if the "winmodem" were to DMA it's
> data into a region of memory and then interrupt the CPU,
> it would seem that the system processor could get an
> interrupt per packet instead of an interrupt per
> character...Just a thought....
Don't forget that the data path for serial ports is still
parallel - it's the UART's job to do all the gubbins to get
it like that though.
The IRQ rate of a soft modem would be lower, but the
processing overhead would add latency and increase CPU load.
IMHO, latency is an unacceptable trade-off (being a Quake
3 Arena player :-)
Would you rather handle:-
a) one byte every 2.27x10^-5 seconds with no processing
latency and a single, simple driver task with a few
lines executed (not time critical task). FIFOs will
reduce the urgency of handling the reception of data.
b) one *huge* chunk of data every 1ms with loads of
processing latency and context switching required
to handle the driver and dsp task with a few
thousand lines of code each irq. This would
probably have to be complete before the next
batch of data arrives (time critical task).
Give a task a high priority and it will lose
I'd go for A.