Motorola PowerQUICC II MPC8280 Series Reference Manual page 980

MCC Exceptions
• CPM bandwidth. Refer to Section 29.8.1.2.5.
• CPM priority. Refer to Section 29.8.1.2.6.
29.8.1.2.1 TDM Clock
Glitches on the TDM clock may be interpreted as an overwhelming number of clocks that
the SI may try to process (amongst other anomalous behavior), thus draining the MCC
FIFOs on that TDM much too quickly. This results in a GUN.
29.8.1.2.2 Synchronization Pulse
A TDM frame length, as programmed in SIRAM, that is shorter than the actual gap between
sync pulses may cause an underrun condition (in other words, if SIRAM programming hits
an entry with SIxRam[LST] set and then encounters dead time before the next sync pulse
on the line). This may result in anomalous behavior in the SI and therefore an underrun
condition.
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.
29.8.1.2.3 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.
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
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MPC8280 PowerQUICC II Family Reference Manual
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