
Data Sheet
June 2001
DSP16410B Digital Signal Processor
92
Agere Systems—Proprietary
Use pursuant to Company instructions
Agere Systems Inc.
4 Hardware Architecture
(continued)
4.13 Direct Memory Access Unit
(DMAU)
(continued)
4.13.7 Interrupts and Priority Resolution
(continued)
The DMAU provides arbitration for requests from many
sources. If multiple requests are pending simulta-
neously, the DMAU completes its current transaction
1
and then provides access to the source that has the
highest priority. The order of priority, from highest to
lowest, is as follows:
1. SWT0 source transaction (SIU0 output) (highest)
2. SWT0 destination transaction (SIU0 input)
3. SWT1 source transaction (SIU0 output)
4. SWT1 destination transaction (SIU0 input)
5. SWT2 source transaction (SIU1 output)
6. SWT2 destination transaction (SIU1 input)
7. SWT3 source transaction (SIU1 output)
8. SWT3 destination transaction (SIU1 input)
9. PIU
10. MMT4 destination write
11. MMT5 destination write
12. MMT4 source fetch
13. MMT5 source fetch (lowest)
MMT channel block transfers that are in progress are
paused if any SWT or PIU bypass channel request
occurs. The single SWT or bypass channel transaction
completes, and then the paused MMT channel block
transfer resumes.
MMT channel priority can be changed by the user
software. The default priority of the MMT channels is
listed above. If both MMT4 and MMT5 require service
at the same time, an MMT4 request has higher priority
than the corresponding MMT5 request. The default
operation does not allow a new MMT request to inter-
rupt an MMT block transfer already in progress, i.e., the
DMAU’s default condition is to start and complete an
MMT block transfer before a new MMT block transfer
can begin. Any MMT block transfer can be interrupted
by any SWT or PIU bypass channel transaction.
The default operation of the MMT channels can be
changed. The HPRIM field (
DMCON0
[15]—
Table 31
on page 70
) is used to select the relative priority of
MMT4 and MMT5. If HPRIM is cleared (the default),
MMT4 has higher priority than MMT5. If HPRIM is set,
MMT5 has the higher priority.
A higher-priority MMT channel can be made to inter-
rupt a lower-priority MMT channel block transfer
already in progress. The MINT field (
DMCON0
[14])
controls this feature. If MINT is cleared, MMT channels
do not interrupt each other, as stated above, and an
MMT block transfer already in progress completes
before another MMT channel request is taken. If MINT
is set, the higher-priority MMT channel can interrupt
the lower-priority channel as determined by the HPRIM
field setting. In a typical application, the higher-priority
channel is assigned to moving small, time-critical data
blocks, and the lower-priority channel is assigned to
large, less time-critical blocks. This feature alleviates
latency that can be incurred due to the transfer of large
data blocks.
1. A request to the DMAU can result in more than one transaction, a transaction being the transfer of one single (16-bit) or double (32-bit) word.