Linux-Hams archive - October 1997: Re: Suggestion for 78.125kb/s, HDLC/AX.25 support w/ Linux
Re: Suggestion for 78.125kb/s, HDLC/AX.25 support w/ Linux
Patrick Arnoul ()
Mon, 6 Oct 1997 10:14:10 +0200
| > It appears some of the software interfaces for some of the popular boards
| > will not support DMA (DMA is probably necessary at 78.125 kb/sec). Perhaps
|
| Not at all. We've successfully interfaced a standard DF9IC modem
| over an enhanced parallel port (EPP; EPP has no DMA, only ECP has)
| at 76k8. HDLC was implemented in software. The measured overhead on
| a 486 machine was very low.
|
| We've used relatively large serial/parallel (and vice versa)
| FIFO's from IDT. The interface generates an interrupt say every
| 10ms, the interrupt handler transfers the whole FIFO contents
| in one go, HDLC decoding it between the EPP cycles.
|
In the good ol'time I was writing HDLC communication software for the 8 Mhz
motorola 6809 uP, DMA started to be necessary for the 256 Kb/s links, and
mandatory for 1024 Kb/s.
I'm glad to see 78.125 Kb/s doesn't need DMA on todays faster PC boards.
BTW, RF bandwidth, multipath, TX/RX switching time is more of a problem to keep
Packet-Radio going faster and faster...
Patrick