![](http://datasheet.mmic.net.cn/380000/-PD98405_datasheet_16745025/-PD98405_190.png)
CHAPTER 5 SAR FUNCTION
190
To store all the packets of VC#I, two free buffers from batch C are required. After the
μ
PD98405 has
stored all the data of packet m to the free buffers, it creates the receive indication for packet m. To this
indication, the first address of batch A is stored as the start address of the packet, along with the packet
size in cell units. The host processes the receive data on the basis of this information and the updated
link pointer.
Packet n only requires one free buffer of batch B. To the receive indication that is issued after packet n
has been stored, the first address and size of batch B are returned.
The host can specify an "alert level (ALERT LEVEL)" to the pool descriptor for the pool that stores the
AAL-5 traffic to manage the receive pool. The
μ
PD98405 decrements the number of batches
remaining in the pool, "REMAINING NO. OF BATCHES IN THE POOL," each time it consumes a
batch. If the number of batches falls to a value less than that specified for ALERT LEVEL, the
μ
PD98405 sets the corresponding bit of the RQA register to 1, sets the RQA bit of the GSR register,
and issues a report to the host by using an interrupt. In response, the host issues the Add_Batch
command to the pool to add a new batch. The ALERT LEVEL function is valid only with the pool used
for AAL-5-type traffic.
When a new cell is received and is about to be transferred to the pool, if the value of "REMAINING
NO. OF BATCHES IN THE POOL" of that pool is already 0, a receive queue underrun occurs. The
μ
PD98405 sets the corresponding bit of the RQU register to 1, sets the RQU bit of the GSR register,
then issues an interrupt if it is not masked.
The initial information for the receive pool is written by the host, using the Indirect_Access command,
to the pool descriptor in control memory. Subsequently, the host uses the Add_Batches command to
add batches to the pool. When the
μ
PD98405 receives the Add_Batches command, it updates the
contents of the pool descriptor. Note that the host does not directly update the value of the pool
descriptor in control memory.
(b) Pool used to store raw cell data
Unlike the pool used to store AAL-5-type traffic, the pool used to store raw cell data does not allocate a
batch to each packet. One free buffer is allocated to each item of raw cell data. When the
μ
PD98405
receives a cell, it sequentially fetches the first free buffer of the first batch of the pool that stores the
cell, and stores the raw cell data to the buffer. When storing raw cell data, the
μ
PD98405 does not
store a receive indication, unlike when storing an AAL-5 packet. Instead, each time it stores a single
raw cell, the
μ
PD98405 sets that bit corresponding to the pool, among bits RCR7 to RCR0 of the GSR
register, to 1, then notifies the host of reception by issuing an interrupt, provided it is not masked.