Motorola PowerQUICC II MPC8280 Series Reference Manual page 1300

TC Layer Programming Mode
35.4.5 Programming and Operating the TC Layer
35.4.5.1 Receive
The TC layer receive operation is enabled by setting TCMODEx[RXEN].
The host software polls the CD bits of each enabled TC layer block to see that its receive
cell delineation state machines are synchronized. For each TC layer block that is
synchronized, the host clears TCERx[CDT]. Once all the enabled TC layer blocks are
synchronized, the host terminates its initialization routine, and the system starts normal
operation.
Once a TC block gets out of synchronization, the corresponding TCGSR[CD] is cleared.
This change then causes a TCER[CDT] interrupt to the host (if enabled in the mask
register—TCMRx).
On the receive path, the TC layer receives the bit stream via the SI and does the following:
1. Attempts to gain synchronization on the ATM cell boundaries by checking each byte
against the HEC calculated on the preceding 32 bits (ATM cell header candidate).
2. Once synchronized:
— Performs the descrambling function on the cell payload (if enabled)
— Performs the coset function on the HEC (if enabled)
— Checks for HEC errors and corrects single HEC errors when found (again, if
enabled). Cells containing multi-bit header errors (at least 2 errors) are
discarded. Idle and unassigned cells are filtered (discarded) when detected (if the
filters are enabled).
Once an ATM cell's processing is complete, it is passed to the TC layer receive FIFO and
the internal TC layer cell counters are updated. The cell is passed from the TC layer receive
FIFO via the internal UTOPIA interface to the FCC2 receive FIFO.
An overrun condition occurs when the TC layer receive FIFO is full and the FCC is unable
to read a cell from it (via the internal UTOPIA interface) before another valid cell is
received. The incoming cell is discarded and TCER[OR] interrupt is sent to the host (if
enabled in the mask register—TCMRx).
35.4.5.2 Transmit
The TC layer transmit operation is enabled by setting TCMODEx[TXEN].
The TC layer requests ATM cells for transmission via the internal UTOPIA interface. Then,
when the ATM cell is passed to the TC layer transmit block, it is stored in the TC layer
transmit FIFO. When the ATM cell is to be transmitted, it is read and processed from the
TC layer transmit FIFO.
35-14
Freescale Semiconductor, Inc.
MPC8280 PowerQUICC II Family Reference Manual
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