Messages in this thread | | | Date | Mon, 20 Sep 1999 00:45:15 +0200 | From | Jamie Lokier <> | Subject | Re: Turning lucent winmodem into soundcard (RT-Linux -when?) |
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Pavel Machek wrote: > Unknown. I think something like 0x400 of buffers is out there. > > What poll frequency do you need and how much time you can miss? > It is modem, so you get about 16KB of data per second. Polling should > probably done so that data are read in 0x100 byte chunks.
Depending on the DSP mode, the I/O buffers vary between 6 and 16 bytes, and the number of buffers transferred at a time also depends on the mode.
The interrupt routine transmits only 6 bytes (this is used for V21 modulation at least), however larger amounts are sent by polling the device and sending at regular intervals. I don't know how long the device buffer is in TAD mode but an experiment shouldn't be hard.
> How much time can I miss? I don't know. That depends on what v34 can > handle.
In general The time we can miss depends on the other end. It's configurable in USR Sportsters: Some S register says how long to wait when a line goes dead before dropping it.
Around here there's a recommendation to increase the value..
For V34 there's the echo cancellor. If we miss, we have to make sure the Tx and Rx sample times are still synchronised, by knowing how many samples didn't go out, so that cancellation keeps working.
To know how many samples didn't go out, I think we have to keep the Tx FIFO full in the interrupt routine. I don't know how to get the count any other way.
-- Jamie
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