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SA-1100 Developer’s Manual 11-13
Peripheral Control Module
11.6.1.5 DMA Buffer B Start Address Register (DBSBn)
The DBSBn is a 32-bit read/write register that contains the starting memory address for buffer B.
This register may be written only while STRTB in the DCSR is zero.
11.6.1.6 DMA Buffer B Transfer Count Register (DBTBn)
The DBTBn is a 32-bit read/write register that contains the current transfer count in bytes for buffer
B. This register may be written only when the STRTB bit for this channel is a zero. The following
figure shows the format of this register; question marks indicate that the values are unknown at reset.
11.6.2 DMA Operation
The DMA controller provides dynamic context switching between active channels on a demand
basis. A context switch may occur when a channel completes a command or when a particular burst
(portion of a transfer) has been completed. For example, if the FIFO in a particular transmit serial
controller is full and cannot accept more data, that channel may be switched out of the active
context in favor of another channel that is requesting service. An active channel may actually go
idle many times as the device is serviced. Channels are serviced in a fixed priority with channel 0
being the highest and channel 5 being the lowest.
Bit31302928272625242322212019181716
Read Reserved
Reset00000000000000?00
Bit1514131211109876543210
Read Reserved
TCB
12
TCB
11
TCB
10
TCB
9
TCB
8
TCB
7
STC
B6
TCB
5
TCB
4
TCB
3
TCB
2
TCB
1
TCB
0
Reset????????????????
Bit Name Description
0..12 TCB<12:0>
Transfer count (buffer B).
This field is a 13-bit value and contains the current transfer count (in bytes) for the transfer
to or from buffer B. The maximum value programmed via this transfer count is 8 Kbyte.
13..31 — Reserved.
These bits are reserved and read as zeros. Writes to this field have no effect.