Peripheral Control Module

11.6.1.5DMA 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.

11.6.1.6DMA 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.

Bit

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Read

 

 

 

 

 

 

 

Reserved

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reset

0

0

0

0

0

0

0

0

0

0

0

0

0

0

?0

0

Bit

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Read

Reserved

TCB

TCB

TCB

TCB

TCB

12

11

10

9

8

 

 

 

 

 

TCB

STC

TCB

TCB

TCB

TCB

TCB

TCB

7

B6

5

4

3

2

1

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.

 

 

 

11.6.2DMA 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.

SA-1100 Developer’s Manual

11-13

Page 163
Image 163
Intel SA-1100 manual DMA Operation, DMA Buffer B Start Address Register DBSBn, DMA Buffer B Transfer Count Register DBTBn