On Thu, 16 Dec 1999 11:30:23 -0500 
 Chris Tribo <t1345@hopi.dtcc.edu> wrote:

 >     Yikes, only one DMA channel is running the entire system? I remember not
 > being able to find a free DMA channel with Windoze. Is there any speculation
 > on what future DMA needs/wants are? I imagine that one would want two DMA
 > channels for the 79C30 currently. At least until we can get full duplex,
 > bidirectional DMA. Am I interpreting that correctly?

Um... the IOASIC has a DMA channel for each of its devices that can do
DMA.  It's simply a case of only supporting DMA SCSI on the IOASIC at
the moment.

Actually, we do use other than one DMA channel; the LANCE on the IOASIC
also does DMA (and we use it; otherwise we wouldn't be able to use the
LANCE :-)

The Zilog serial ports can also do DMA, and there are IOASIC DMA channels
for them (one transmit and receive per UART channel).

The 79c30 can do DMA, and there are IOASIC DMA channels for it, too.

/* 
 *  Register offsets (slot 1)
 */

#define IOASIC_SCSI_DMAPTR              IOASIC_SLOT_1_START+0x000
#define IOASIC_SCSI_NEXTPTR             IOASIC_SLOT_1_START+0x010
#define IOASIC_LANCE_DMAPTR             IOASIC_SLOT_1_START+0x020
#define IOASIC_SCC_T1_DMAPTR            IOASIC_SLOT_1_START+0x030
#define IOASIC_SCC_R1_DMAPTR            IOASIC_SLOT_1_START+0x040
#define IOASIC_SCC_T2_DMAPTR            IOASIC_SLOT_1_START+0x050
#define IOASIC_SCC_R2_DMAPTR            IOASIC_SLOT_1_START+0x060
#define IOASIC_FLOPPY_DMAPTR            IOASIC_SLOT_1_START+0x070
#define IOASIC_ISDN_X_DMAPTR            IOASIC_SLOT_1_START+0x080
#define IOASIC_ISDN_X_NEXTPTR           IOASIC_SLOT_1_START+0x090
#define IOASIC_ISDN_R_DMAPTR            IOASIC_SLOT_1_START+0x0a0
#define IOASIC_ISDN_R_NEXTPTR           IOASIC_SLOT_1_START+0x0b0
.
.
.

DECstations might be weird sometimes, but they suck far less than PCs :-)

        -- Jason R. Thorpe <thorpej@nas.nasa.gov>