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CHAPTER 5 SAR FUNCTION
249
Command description
The host uses the Add_Batches command to add unused batches to one of the 32 receive free buffer
pools. This command is used to manipulate the command extension register (CER/CER_L). The host first
writes "BATCH POINTER" to the command extension register, then writes a command to the command
register (CMR/CMR_L).
Before issuing an Add_Batches command, the host must perform some tasks. The host allocates a batch
to be added and the related buffer in system memory. If more than one batch is to be added, they must be
linked to one another in advance. The host writes the link pointer, at the last batch in the existing batch list
in the pool, to the start address of the batches. Once this task has been completed, the host can issue the
Add_Batches command.
The operation of the
μ
PD98405 after receiving the Add_Batches command differs depending on whether
any unused batches remain in the targeted pool at that time.
(a) If any unused batches remain in the pool
(If "REMAINING NUMBER OF BATCHES" of the pool descriptor is set to other than "0")
The
μ
PD98405 adds batches by number set in "NUMBER OF BATCHES" to "REMAINING NUMBER
OF BATCHES" of the pool descriptor. At this time, the "batch link pointer" of the remaining batches
must be changed to the first address of the batches to be newly added (see
Figure 5-55
).
The batches to be newly added must be chained by the link pointer.
Figure 5-55. Host Operation before Issue of Add_Batches Command
Batch
Batch link pointer
Last batch
A
Added batch list
Changed by host
First batch to be
added
Remaining batch list
Address A
Chained in
advance by host