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CHAPTER 5 SAR FUNCTION
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(2) Raw cell transmission
When transmitting a non-AAL-5 packet other than an OAM F5 cell, the host must clear the "AAL" bit of the
packet descriptor to 0 and set the PTI field to "0xx" (000 to 011), thus indicating a user data cell. The
μ
PD98405 does not execute AAL-5 trailer operation, nor does it add a trailer to the packet, if the "AAL" bit
of the packet descriptor is set to 0. The
μ
PD98405 performs raw cell transmission during which it
repeatedly reads 48 bytes of a transmission segment from the data buffer, creates a cell, then transmits the
cell to the PHY layer device. One packet of transmit data can consist of up to 65,535 bytes and a data
buffer can be configured in multi-buffer mode. Note, however, that for raw cell transmission, the host must
use a 1-packet transmission buffer of a size that is an integer multiple of 48 bytes. Therefore, in the "SIZE"
field of the packet descriptor, set a 48-byte integer multiple. In multi-buffer mode, the total size of the 1-
packet transmission buffers that constitute a multi-buffer must be set to a size equal to an integer multiple
of 48 bytes. To transmit data of a size other than an integer multiple of 48 bytes, the host must first append
dummy data (all zeros) to that data to make its size a multiple of 48 bytes.
If necessary, the host sets the "C10" bit of the packet descriptor to 1 to enable the CRC-10 operation
insertion function of the
μ
PD98405. When this function is enabled, the
μ
PD98405 executes a CRC-10
operation on the 46 bytes and 6 bits of the 48-byte segment read from the data buffer of system memory,
overwriting the last 10 bits of the cell with the result as an error code. When preparing non-AAL-5 data in
system memory, the host must insert dummy data into the 10 bits of the segment units that are to be
overwritten by CRC-10.
During raw cell transmission, the last cell is also transmitted according to the pattern specified in the PTI
field of the packet descriptor. The least significant bit of the PTI field is thus not automatically changed to
"1."
Note the following when performing raw cell transmission.
For Raw cell transmission, the "AAL" bit must be set to 0.
For Raw cell transmission, the size of the 1-packet transmission buffer must be set to an integer
multiple of 48 bytes (other than 0).