
CHAPTER 5 SAR FUNCTION
191
Because the
μ
PD98405 does not notify the host of the address of the free buffer in which the data has
been stored, the host must store the address of the free buffer which was used previously. A single
pool can be specified to store raw cell data for two or more VCs. In such a case, cells are stored in
free buffers in the order in which they are received, regardless of the VC. For a pool used to store
AAL-5 packets, the "ADDRESS" field of the pool descriptor stores the start address of the batch to
which the
μ
PD98405 will store the next data. For a pool used to store raw cell data, however, the
"ADDRESS" field stores the address of the free buffer in which the next data will be stored. If all free
buffers in the batch have been used up, the
μ
PD98405 will store the raw cell data in the next batch.
Figure 5-40. Structure of Raw Cell Data Storing Pool
(When specified to store raw cell data of VC#I and VC#J in the same pool)
Batch A
Batch B
31
31
0
0
64 bytes
VC#I
Raw cell data 1
VC#J
Raw cell data 1
VC#I
Raw cell data 2
Batch link pointer
Buffer address 1
Buffer address 3
Buffer address 2
Size
Size
Size
Batch link pointer
Buffer address 1
Buffer address 3
Buffer address 2
Size
Size
Size
The pool that stores raw cell data does not have a function for monitoring ALERT LEVEL to indicate
the number of remaining batches. Only the RQU interrupt function, that indicates an underflow of the
transmit queue, is valid.
For an explanation of the raw cell data, see
Section 3.3.3
. An AAL-5 packet cannot be stored to a
pool specified to store raw cell data. Note that a single pool cannot contain more than one type of
data.
(3) T1 timer (reassembly timer)
The
μ
PD98405 supports a function for specifying the time required for one packet to arrive by using the
hardware watchdog timer. This function is called the T1 timer (reassembly timer) function. The user sets
the time allowed for the last cell to arrive, after the first cell of the packet to a register. The
μ
PD98405
monitors whether packet reception is performed within the set time. If the time is exceeded, reception of
that packet is stopped, and a T1 error is reported to the host as the receive indication.