MPC8280 datasheet(930/1386 Pages) FREESCALE

930 / 1386 page

Multi-Channel Controllers (MCCs)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

29-40

Freescale Semiconductor

29.8.1.2.4

MCC Initialization

CPCR commands for the MCC (such as Init Tx Parameters and Init Rx Parameters) must be issued to cover

all MCC channel numbers that appear in either the SIRAM or superchannel table before that channel

number is used on an active TDM. Note that the command initializes 32 channels at a time, starting with

the channel number given in the command. All channels used in any fashion must be initialized by the

Init Tx parameters and the Init Rx parameters command.

Before a TDM is enabled to use an MCC channel, the following must be initialized:

•

Global MCC parameters

•

Channel Extra Parameters

•

Channel-Specific Parameters

•

Super-Channel Table (if appropriate) and registers

If the MCC has invalid data in any of these areas when the SI tries to talk to the MCC, a GUN is one of

the possible symptoms. Before a TDM is programmed to use an MCC channel, the channel-specific fields

RSTATE and TSTATE must either contain the start value or “STOP TX” and “STOP RX” commands must

be issued to that channel. It is not a valid condition to leave RSTATE and TSTATE unitialized before TDM

operation using that channel

29.8.1.2.5

CPM Bandwidth

If the CPM is overloaded, the MCC is usually one of the first communications controllers to exhibit

problems, often in the form of the GUN. The MCC's sensitivity to bandwidth issues is due to the

shallowness of the FIFOs and the CPM prioritization of the MCC TX.

29.8.1.2.6

CPM Priority

It is possible for the MCC to experience a GUN due to prioritization in the CPM. See Section 14.3.5,

“Peripheral Interface,” for details on the CPM prioritization scheme. There are some options available for

altering how the CPM peripheral prioritization works. These options provide the opportunity for the user

to raise the priority of the MCC itself or lower the priority of other peripherals.

RCCR[MCCPR] controls the MCC priority in relation to other CPM peripherals (refer to Section 14.3.7,

“RISC Controller Configuration Register (RCCR)”). When MCCPR is set, the MCCs are constantly at

emergency priority level within the CPM prioritization scheme. If used, this configuration should be tested

to ensure that the setting of MCCPR does not have adverse effects on the performance of other peripherals

being used in an application. When MCCPR is cleared, the normal priority scheme is be used (refer to

Section 14.3.5, “Peripheral Interface”).

Each FCC FIFO has threshold values, determined by the mode it is using, for determining normal and

emergency CPM request prioritization. When an FCC is in emergency mode, that FCC's TX or RX request

may have higher priority than MCC TX or RX. When FCC1 in particular is in emergency priority mode,

it will always be of higher priority than an MCC. This opens up the possibility of the FCC starving out the

MCC if the FCC continues to be overutilized. This can lead to a GUN. To help alleviate this situation,

setting FPSMR[TPRI] prevents the FCC’s TX from going into emergency mode and can minimize the risk

of global underrun.

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