Vax 613 0S Manuel d'instructions Page 79

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Note
The scatter/gather map acts on a DMA read or write operation, only if the
scatter/gather bit is set for that device in the TURBOchannel interface’s
IOSLOT register (see Section 3.3.1).
5.3 Writing and Reading Scatter/Gather Map Entries
Software must not write to a map entry while DMA is in progress through that
entry. When software writes an entry, it must supply the following data in the
low 24 bits:
04 03 0021 2023 22
MR−0081−93RAGS
V F X PPN XXXX
Bit Description
3:0 Discarded and ignored in the parity computation
20:4 Physical page number
21 Discarded because the hardware calculates the parity bit.
22 Funny bit
23 Valid bit
Software can read any scatter/gather map entry while DMA is in progress. When
software reads a scatter/gather map entry, the following bits are returned:
04 03 0021 2023 22
MR−0082−93RAGS
V P PPN UNP
U
N
P
Bit Description
3:0 UNPREDICTABLE.
20:4 Physical page number
21 Parity bit
22 Funny bit
23 Valid bit
Scatter/Gather (Virtual DMA) RAMs (400/500/600/700/800/900 Models) 5–3
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