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CHAPTER 5 SAR FUNCTION
199
<1>
OAM F5 and RM cell data
When the user sets the OD bit of the VC table to "0" (to enable the reception of an OAM F5 cell) and
the
μ
PD98405 receives a cell in which PTI field of the header is of "1XX" format, which indicates
OAM F5 and resource management cells, it creates raw cell data and stores it to pool 0. The RCR0
bit of the GSR register is set to 1 and an interrupt is generated provided it is not masked. The
μ
PD98405 always stores these cells to pool 0. If the OD bit is cleared to "0," therefore, pool 0 must
be set as a pool that stores raw cell data.
The OD bit can be set to 0 regardless of whether the A/R bit is set to 0 or 1. For example, when OD
= 0, A/R = 1, and "POOL NO." = 8, a received cell for which the PTI field contains a user data code is
stored in pool 8 as an AAL-5 packet. If a cell for which the PTI field contains an OAM F5 or RM cell
code is received, that cell is stored in pool 0 as raw cell data. If at least one channel receives OAM
F5 or RM cell, however, pool 0 is used exclusively to store raw cell data. In such a case, a pool other
than pool 0 must be specified for storing AAL-5 packets. A single pool cannot contain both raw cell
data and an AAL-5 packet.
Remark
If a receive VC uses the ABR service (the ABR bit is set to 1), RM cells received by this
VC are processed as RM cells for ABR. Even if the OD bit is set to 0, the
μ
PD98405 does
not store RM cells in pool 0. Even if the OD bit is set to 1, the
μ
PD98405 does not discard
RM cells. Instead, it processes them as RM cells for ABR.
<2>
Non-AAL-5 traffic
If the A/R bit of a VC table that has been opened by the user is cleared to "0," each time a cell of the
VC is received, it is transferred to system memory as raw cell data. When raw cell data is received,
the user can specify any of pools 0 through 7 for "POOL NO.". The specified pool must be prepared
to store the raw cell data. This function allows the user to receive cells of non-AAL-5 traffic. The
assembly of a packet from raw cell data and trailer processing are executed by software in system
memory. When non-AAL-5 traffic is received as raw cell data, processing is completed in cell units
and no receive indication for each packet is issued, unlike in the case of AAL-5 packets. An error
report function such as that supported for AAL-5 packet reception is, therefore, not supported for
non-AAL-5 traffic. Even if a cell is discarded due to a free buffer underflow or receive FIFO overrun,
the
μ
PD98405 does not report it to the host, and the monitoring of "MAX. NUMBER OF SEGMENTS"
and the detection of a T1 error are disabled. An RQU interrupt is, however, issued and an indication
for reporting the completion of the Deactivate_Channel command is also issued.
During raw cell reception with A/R = 0, if a cell for which the PTI field contains an OAM F5 or RM cell
code is received, that cell is stored in pool 0, provided OD is set to 0.