Freescale Semiconductor MPC8260 - Manual (Page 888)

Multi-Channel Controllers (MCCs)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
28-40 Freescale Semiconductor
28.8.1.2 Global Transmitter Underrun (GUN)
A global underrun (GUN) event indicates that the MCC’s transmit FIFO array experienced an underrun
condition. This is not due to a lack of ready transmit buffer descriptors (as in the UN condition in an
interrupt queue entry); rather, it indicates a hardware latency issue which could be caused in several ways.
It is not possible to determine exactly which channel's FIFO experienced the underrun, therefore a GUN
is considered a global event affecting that entire MCC. Following the assertion of MCCE[GUN], the MCC
stops transmitting data on all channels and all ones are sent instead. The MCC must be reset either through
an MCC RESET command or a CPM RESET after this error and then the MCC may be reinitialized.
There are several possible causes for an MCC GUN error:
• Glitching on the TDM clock. Refer to Section 28.8.1.2.1.
• Synchronization pulse (sync pulse). Refer to Section 28.8.1.2.2.
• Misprogramming of SIRAM. Refer to Section 28.8.1.2.3 and Section 28.8.1.2.4.
• CPM bandwidth. Refer to Section 28.8.1.2.5.
• CPM priority. Refer to Section 28.8.1.2.6.
28.8.1.2.1 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.
28.8.1.2.2 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.
12 MRF Maximum receive frame length violation. This interrupt occurs when more bytes are received than
the value specified in MFLR. This interrupt is generated as soon as the MFLR value is exceeded;
the remainder of the frame is discarded
13 RXF Rx frame. A complete HDLC frame has been received.
14 BSY Busy. A frame was received but was discarded due to lack of buffers.
15 RXB Rx buffer. A buffer has been received on this channel that was not the last buffer in frame. This
interrupt is also given for different error types that can happen during reception. Error conditions are
reported in the RxBD.
16–17 — Reserved, should be cleared.
18–25 CN Channel number. Identifies the requests channel index (0–255).
26–31 — Reserved, should be cleared.
Table 28-19. Interrupt Circular Table Entry Field Descriptions (continued)
Bits Name Description