Motorola PowerQUICC II MPC8280 Series Reference Manual page 1007

30.10 FCC Interrupt Handling
The following describes what usually occurs within an FCC interrupt handler:
1. When an interrupt occurs, read FCCE to determine interrupt sources. FCCE bits to
be handled in this interrupt handler are normally cleared at this time.
2. Process the TxBDs to reuse them if the FCCE[TX,TXE] were set. If the transmit
speed is fast or the interrupt delay is long, more than one transmit buffer may have
been sent by the FCC. Thus, it is important to check more than just one TxBD
during the interrupt handler. One common practice is to process all TxBDs in the
interrupt handler until one is found with R set.
3. Extract data from the RxBD if FCCE[RX, RXB, or RXF] is set. If the receive speed
is fast or the interrupt delay is long, the FCC may have received more than one
receive buffer. Thus, it is important to check more than just one RxBD during
interrupt handling. Typically, all RxBDs in the interrupt handler are processed until
one is found with E set. Because the FCC prefetches BDs, the BD table must be big
enough such that always there will be another empty BD to prefetch.
4. Clear FCCE.
5. Continue normal execution.
30.10.1 FCC Transmit Errors
There are four errors in the FCC transmitter that make it necessary for software to act on
the transmitter before correct operation can continue. The errors are as follows:
• CTS-lost indication in HDLC transmitter (use re-initialization procedure)
• Underrun in any of the serial FCC transmitter protocols (use re-initialization
procedure)
• Late collision in fast Ethernet transmitter (use recovery or re-initialization
procedure)
• Expiration of retry limit in fast Ethernet (use recovery or re-initialization procedure)
In addition to status bits in the current TxBD, these errors are reported via the TXE event
bit in the FCCE as a convenience for the user to implement error handling. TXE is a safe
indication that a recovery or re-initialization procedure must be started.
30.10.1.1 Re-Initialization Procedure
1. Disable the FCC transmission by clearing GFMR[ENT].
2. Remember the TBPTR value taken from the FCC parameter RAM.
3. Issue an "INIT TX PARAMS" command using the CPCR.
4. Restore the remembered TBPTR into the FCC parameter RAM.
MOTOROLA Chapter 30. Fast Communications Controllers (FCCs)
Freescale Semiconductor, Inc.
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FCC Interrupt Handling
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