YMF724 ETC, YMF724 Datasheet - Page 38

• Manufacturer Part Number: YMF724
• Description: high performance audio controller for the PCI Bus
• Manufacturer: ETC

YMF724F
3. DMA Emulation Protocol
3-1. PC/PCI
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-1, 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-1 supports both protocols for transferring SB Pro sound data on the PCI bus.
DS-1 provides two signals, PCREQ# and PCGNT# to realize the PC/PCI. The format of the signals is
shown below. DS-1 asserts PCREQ# and sets PCREQ# to “HIGH” using the PCICLK corresponding to the
DMA channel it is going to use.
In addition, DS-1 determines whether the next PCI I/O cycle is its own from the channel information that is
encoded in PCGNT#.
PCGNT# is encoded as follows.
DS-1 supports only 8-bit DMA channels (DMA Channel 0-3). It also only supports Single DMA transfer.
PCICLK
REQ#
GNT#
0ns
start
bit2
0
0
0
0
1
1
1
1
CH0
bit1
0
0
1
1
0
0
1
1
CH1
100ns
GNT# Encoding
CH2
bit0
0
1
0
1
0
1
0
1
CH3
GNT# Bits
DMA Channel 0
DMA Channel 1
DMA Channel 2
DMA Channel 3
Reserved
DMA Channel 5
DMA Channel 6
DMA Channel 7
CH4
-38-
CH5
200ns
CH6
CH7
300ns
start
bit0
bit1
400ns
bit2
January 14, 1999