Serial Management Controllers (SMCs)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
29-26
Freescale Semiconductor
29.4.8
Handling Errors in the SMC Transparent Controller
The SMC uses BDs and the SMCE to report message transmit and receive errors.
29.4.9
SMC Transparent Receive BD (RxBD)
Using BDs, the CP reports information about the received data for each buffer and closes the current
buffer, generates a maskable interrupt, and starts to receive data into the next buffer after one of the
following events:
•
An overrun error occurs.
•
A full receive buffer is detected.
•
The
ENTER
HUNT
MODE
command is issued.
Figure 29-13
shows the SMC transparent RxBD format.
Table 29-14
describes SMC transparent RxBD fields.
Table 29-13. SMC Transparent Error Conditions
Error
Descriptions
Underrun
The channel stops sending the buffer, closes it, sets UN in the BD, and generates a TXE interrupt if
it is enabled. The channel resumes sending after a
RESTART
TRANSMIT
command. Underrun cannot
occur between frames.
Overrun
The SMC maintains an internal FIFO for receiving data. If the buffer is in external memory, the CP
begins programming the SDMA channel when the first character is received into the FIFO. If a FIFO
overrun occurs, the SMC writes the received data character over the previously received character.
The previous character and its status bits are lost. Then the channel closes the buffer, sets OV in
the BD, and generates the RX interrupt if it is enabled. Reception continues as normal.
0
1
2
3
4
5
6
7
13
14
15
0
E
—
W
I
—
CM
—
OV
—
2
Data Length
4
Rx Buffer Pointer
6
Figure 29-13. SMC Transparent Receive BD (RxBD)
Table 29-14. SMC Transparent RxBD Field Descriptions
Bits
Name
Description
0
E
Empty.
0 The buffer is full or reception was aborted due to an error. The core can read or write any fields
of this RxBD. The CP does not use this BD while E = 0.
1 The buffer is empty or is receiving data. The CP owns this RxBD and its buffer. Once E is set, the
core should not write any fields of this RxBD.
1
—
Reserved, should be cleared.
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