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dma: comment

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This commit is contained in:
cinap_lenrek 2011-05-18 20:02:17 +00:00
parent df687d3840
commit f5b15ebcd3
1 changed files with 5 additions and 2 deletions
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7
sys/src/9/pc/dma.c
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@ -212,12 +212,15 @@ dmasetup(int chan, void *va, long len, int flags)
else
xp->len = 0;
mode = ((flags & DMAREAD) ? 0x44 : 0x48) | /* read or write */
((flags & DMALOOP) ? 0x10 : 0) | /* auto init mode */
chan;
/*
* this setup must be atomic
*/
ilock(dp);
mode = ((flags & DMAREAD) ? 0x44 : 0x48) | ((flags & DMALOOP) ? 0x10 : 0) | chan;
outb(dp->mode, mode); /* single mode dma (give CPU a chance at mem) */
outb(dp->mode, mode);
outb(dp->page[chan], pa>>16);
outb(dp->cbp, 0); /* set count & address to their first byte */
outb(dp->addr[chan], pa>>dp->shift); /* set address */