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YMF744B
February 3, 1999
-44-
3. DMA Emulation Protocol
The former synthesizer LSI for the ISA bus such as the Sound Blaster used the DMA controller (8237: ISA
DMAC) on the system to transfer the sound data from/to the host.
For DS-1S, however, ISA DMAC must be used to transfer the sound data to the Sound Blaster Pro Block of
the Legacy Audio Block.
Because signals to connect to the ISA DMAC are generally not available on the PCI bus, there are two ways
proposed from the industry to emulate the ISA DMAC on the PCI bus. One is PC/PCI and the other is D-
DMA.
DS-1S supports both protocols for transferring SB Pro sound data on the PCI bus.
3-1. PC/PCI
DS-1S provides two signals, PCREQ# and PCGNT# to realize the PC/PCI. The format of the signals is
shown below. DS-1S asserts PCREQ# and sets PCREQ# to “HIGH” using the PCICLK corresponding to
the DMA channel it is going to use.
In addition, DS-1S determines whether the next PCI I/O cycle is its own from the channel information that is
encoded in PCGNT#.
start CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7
start bit0 bit1 bit2
0ns 100ns 200ns 300ns 400ns
PCICLK
REQ#
GNT#
PCGNT# is encoded as follows.
GNT# Encodin
g
bit2 bit1 bit0
GNT# Bits
000
DMA Channel 0
001
DMA Channel 1
010
DMA Channel 2
011
DMA Channel 3
100
Reserved
101
DMA Channel 5
110
DMA Channel 6
111
DMA Channel 7
DS-1S supports only 8-bit DMA channels (DMA Channel 0-3). It also only supports Single DMA transfer.