Utopia Receive Overview - Freescale Semiconductor MPC850 User Manual

UTOPIA Operation
For AAL0, the transmitter simply copies the cell (except the HEC) prepared by the user
from the channel's buffer and sends it through the UTOPIA interface. The ATM controller
can optionally generate CRC10 on the cell payload and place the result at the end of the
payload (CRC10 field). This feature is used to support OAM CRC10; refer to the ITU
specification I.610 for additional details.
If, however, the current active channel's buffer is not ready, the transmit process ends and
no cell is sent to the PHY. The PHY is responsible for generating an idle cell in an empty
cell slot. An empty cell slot will continue to be generated each time the APC schedules this
channel in the transmit queue until either a buffer is made ready or a
DEACTIVATE CHANNEL
additional information about ATM controller commands.
The ATM controller does not generate the HEC in UTOPIA
mode. The transmitter sends a dummy byte value (0x00) in
place of the HEC; the PHY is responsible for the actual
calculation of the HEC.

36.6.2 UTOPIA Receive Overview

The UTOPIA receive process begins when the PHY asserts the receive cell available signal
(RxClav), indicating that the PHY has a complete cell in its receive FIFO buffer. The ATM
controller first receives the cell header through the UTOPIA interface. The receiver
translates the header address (GFC/VPI/VCI/PTI) to a channel number using either a
look-up table in dual-port RAM, address compression tables in external RAM, or an
external content-addressable memory (CAM). A cell header that has no match is treated as
an AAL0 cell and is passed to the global raw cell queue (usually defined by convention to
be channel number 0). If the cell header is matched to an active channel, the payload (48
bytes) is copied to the current buffer, the CRC is calculated (optional for AAL0), and the
RCT parameters are updated. If, however, the current buffer is not empty, a busy interrupt
is optionally generated and the cell is discarded.
For AAL5, when a cell with an end-of-frame marker (indicated by PTI[1]) is received, the
receiver separates the trailer of the CPCS-PDU from the user data. The pads are removed
as required, the length field is checked against the length which was calculated during the
frame receive, the CPCS-UU and CPI are copied to the RxBD, and the buffer is closed. An
interrupt is optionally generated to declare the end of received frame. If a CRC or length
error occurs, it is marked in the RxBD and an interrupt is optionally generated.
For AAL0, the ATM controller copies the cell (except the HEC) from the UTOPIA interface
to the channel's current buffer and optionally performs a CRC10 check on the cell payload.
The CRC10 option is used to support OAM cell checking (by host software) according to
the ITU specification I.610.
command is issued. See Section 39.3, "ATM Commands," for
NOTE:
MPC850 Family User's Manual
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