MPC8280 datasheet(931/1386 Pages) FREESCALE

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Multi-Channel Controllers (MCCs)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

29-41

29.8.1.2.7

Bus Latency

A GUN may also occur if the external memory bus bandwidth is insufficient for the system. Factors could

include a bus that is too slow or external masters keeping the bus for extended periods of time. Bus

parking master and bus arbiter configurations as described in Section 4.3.2, “System Configuration and

Protection Registers,” should also be considered as factors when making sure the CPM is properly

prioritized for bus access.

29.8.1.3

Recovery from GUN Errors

The GUN error is considered fatal because it cannot be determined which channel was at fault. The MCC

RESET command in the CP command register [CPCR] provides a hard reset to the MCC FIFOs. Refer to

the following table.

29.8.1.4

Global Overrun (GOV)

An MCC receiver global overrun (GOV) is the receive version of the transmit GUN. Due to different

prioritization and implementation of MCC RX, the likelihood of a GOV occurring is less than a the

likelihood of a GUN. Despite this, all possible causes and recovery procedures apply.

29.9

MCC Buffer Descriptors

Each MCC channel requires two BD tables (one for transmit and one for receive). Each BD contains key

information about the buffer it defines. The BDs are accessed by the MCC as needed; BDs can be added

dynamically to the BDs chain. The RxBDs chain must include at least two BDs; the TxBD chain must

include at least one BDs.

The MCC BDs are located in the external memory.

Table 29-20. GUN Error Recovery

Step

Action

Disable the TDM by clearing the appropriate enable bit in SIxGMR[4-7].

Issue the MCC RESET command.

Issue the INIT RX AND TX command to cover the channels in use.

Reprogram the specific MCC channel, global parameters, and any BDs that need to be updated.

Enable TDM by setting appropriate bit.

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