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CS4281 Programming Manual
DS308PRM1
123
Confidential Draft
3/7/00
BPFF
Byte Pointer flip-flop. This bit keeps track of upper vs. lower byte in DMA CCLS address and
count values. This bit is reset by write snoops to 0Ch when any
C1xxx
or
C2xxx
bit
is set.
BPFF
is XORed (flipped) by any access claimed or snooped by
C1xxx
bits (except the
Address Page location), and the other registers in the 0 to 7 range
snooped by
C2WSE
or
C2RSE
.
C3WSE
CCLS 3 Write Snoop Enable: When set, the CCLS I/O Trap logic snoops the writes to the
Single Mask register (0Ah) and the Mode register (0Bh). The lower two
bits of these snoops indicate which DMA the data is for. If the lower two bits are set to the
legacy DMAn controller (
IOTCR.DMA
bits), then the data is sent to the appropriate DMAn
register. Instead of claiming the I/O write transaction, the CS4281 captures data written to the
snooped I/O range and stores it in the appropriate register, just as if the I/O location was
actually trapped. The actual legacy 8237 will claim these transactions.
0 = Write snooping disabled (reset default)
1 = Write snooping enabled
C4RE
CCLS 4 Read Enable: When set, read trapping is enabled for the CCLS assigned legacy
DMAn controller (
IOTCR.DMA
) Status register at 08h and Multi-engine mask
register at 0Fh. Setting this bit causes a complicated series of steps which starts
with telling the host to retry the cycle. Then, for the Status register, the CS4281 reads the real
8237 location 08h, combines the other engine status with the proper status bits for the legacy
DMAn engine located in HDSRn, and stores the data in DLSR. When the host retries the read
to 08h, the DLSR register is read. Note that this host-retry mechanism cannot interfere with
any DMA cycles that may occur during this procedure. The Multi-Engine mask register read
responds similarly except that the host address read is 0Fh. The current legacy DMAn mask
register is DCRn, and the combined legacy mask register that is finally read by the host when
retried is DLMR. Note that any DMA activity has to be supported while the re-try is in
progress.
0 = Read trapping disabled (reset default)
1 = Read trapping enabled
C4WSE
CCLS 4 Write Snoop Enable: When set, the CCLS I/O Trap logic snoops the writes to the
Multi-Engine Mask register (0Fh) and the Clear-All Masks register
(0Eh). For the Multi-Engine Mask, the legacy DMAn controllers bit is redirected to
bit 0 of DMRn. Instead of claiming the I/O write transaction, the CS4281 captures data written
to the snooped I/O range and stores it in the appropriate register, just as if the I/O location was
actually trapped. The actual legacy 8237 will claim these transactions. For the Clear-All Mask
register, any write to this address clears
DMRn.MSK
. The actual data for 0Eh write
snoops is irrelevant.
0 = Write snooping disabled (reset default)
1 = Write snooping enabled
D
ra
ft
Содержание CS4281
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