Handling Errors In The Smc Transparent Controller; Smc Transparent Receive Bd (Rxbd) - Freescale Semiconductor MPC850 User Manual

SMC in Transparent Mode

30.4.8 Handling Errors in the SMC Transparent Controller

The SMC uses BDs and the SMCE to report message transmit and receive errors.
Table 30-13. SMC Transparent Error Conditions
Error
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
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.

30.4.9 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
Figure 30-13 shows the SMC transparent RxBD format.
0 1
E
Offset + 0 —
Offset + 2
Offset + 4
Offset + 6
Figure 30-13. SMC Transparent Receive BD (RxBD)
Table 30-14 describes SMC transparent RxBD fields.
Table 30-14. SMC Transparent RxBD Field Descriptions
Bits Name
E
0 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.
command is issued.
2 3 4 5
W I CM
—
MPC850 Family User's Manual
Descriptions
command. Underrun cannot occur
RESTART TRANSMIT
6 7 8 9 10
—
Data Length
Rx Buffer Pointer
Description
11 12 13 14
OV
15
—