Freescale Semiconductor MPC8260 - Manual (Page 889)

Multi-Channel Controllers (MCCs)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 28-41
To avoid these cases, pad out the SIRAM programming with “null entries,” entries with no CPM peripheral
specified (MCC=0 and CSEL = 0000 in SIRAM entry) at the end of the SIRAM programming. Make the
null SIRAM entries represent the appropriate amount of time so that the SI frame length matches the gap
between sync pulses.
28.8.1.2.3 SIRAM Programming
Failure to follow SIRAM programing guidelines can result in erratic behavior or possibly GUN errors. The
following is a list of common programming errors:
• Failing to set “LAST” in the final entry of an even-numbered total of SIRAM entries (i.e. there
cannot be an odd total of SIRAM entries for a TDM)
• Programming an SIRAM entry to use an un-initialized MCC channel (or if the MCC as whole has
not been initialized with the appropriate “INIT TX RX” commands).
• Programming an SIRAM entry to use an MCC channel that is not assigned to that particular TDM.
• Using a channel too often (which would overload the FIFO) without going to superchannels.
• Turning on too many MCC channels at once in the SIRAM (we suggest not to enable more than 32
channels per TDM frame's worth of time when you are first programming the SI).
• Other programming errors, such as incorrect values in the SIRAM entries, etc.
28.8.1.2.4 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
28.8.1.2.5 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.