Date: Tue, 22 Jul 1997 15:32:17 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: hackers@freebsd.org, multimedia@freebsd.org Subject: polling the status of a dma channel Message-ID: <199707221332.PAA22798@labinfo.iet.unipi.it>
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Recently I and others had a need to poll the status of a dma channel
to determine if a transfer was proceeding or not.
I came out with the following function which I placed in
/sys/i386/isa/isa.c -- the place I believe it belongs to.
Maybe we should consider adding this function to isa.c ? It would be
useful for the sound driver and probably other drivers as well.
Cheers
Luigi
-------------
/*
* isa_dmapoll returns the number of pending bytes for a dma transfer
* on the given channel.
*/
int
isa_dmapoll(int chan)
{
u_long phy = 0 ;
u_long cnt = 0 ;
u_long flags ;
int waport;
if (dma_inuse & (1 << chan) == 0) {
printf("chan %d not acquired\n", chan);
return -1 ;
}
if (dma_busy & (1 << chan) == 0) {
printf("chan %d not busy\n", chan);
return -2 ;
}
flags = splhigh();
if ((chan & 4) == 0) { /* 8-bit channel */
outb(DMA1_FFC, 0);
waport = DMA1_CHN(chan);
phy= inb(waport) + (inb(waport) <<8) + (inb(dmapageport[chan]) <<16 );
cnt = inb(waport+1) + (inb(waport+1)<<8) +1;
cnt &= 0xffff ;
} else {
outb(DMA2_FFC, 0);
waport = DMA2_CHN(chan - 4);
phy= inb(waport) + (inb(waport) <<8) + (inb(dmapageport[chan]) <<16 );
cnt = inb(waport+1) + (inb(waport+1)<<8) + 1;
phy <<= 1;
cnt <<= 1;
cnt &= 0x1ffff ;
}
splx(flags);
return cnt ;
}
Cheers
Luigi
-----------------------------+--------------------------------------
Luigi Rizzo | Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it | Universita' di Pisa
tel: +39-50-568533 | via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522 | http://www.iet.unipi.it/~luigi/
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