Unexpected Receive Frame-Sync Pulse
McBSP Exception/Error Conditions
4-6
SPRU592E
Any one of three cases can occur:
-
Case 1:
Unexpected internal FSR pulses with RFIG = 1 in RCR2. Receive
frame-sync pulses are ignored, and the reception continues.
-
Case 2:
Normal serial port reception. Reception continues normally
because the frame-sync pulse is not unexpected. There are three possible
reasons why a receive operation might
not
be in progress when the pulse
occurs:
J
The FSR pulse is the first pulse after the receiver is enabled
(RRST = 1 in SPCR1).
J
The FSR pulse is the first pulse after DRR[1,2] is read, clearing a
receiver full (RFULL = 1 in SPCR1) condition.
J
The serial port is in the interpacket intervals. The programmed data
delay for reception (programmed with the RDATDLY bits in RCR2)
may start during these interpacket intervals for the first bit of the next
word to be received. Thus, at maximum frame frequency, frame
synchronization can still be received 0 to 2 clock cycles before the first
bit of the synchronized frame.
-
Case 3:
Unexpected receive frame synchronization with RFIG = 0
(frame-sync pulses not ignored). Unexpected frame-sync pulses can
originate from an external source or from the internal sample rate
generator.
If a frame-sync pulse starts the transfer of a new frame before the current
frame is fully received, this pulse is treated as an unexpected frame-sync
pulse, and the receiver sets the receive frame-sync error bit (RSYNCERR)
in SPCR1. RSYNCERR
can be cleared only by a receiver reset or by a
write of 0 to this bit.
If you want the McBSP to notify the CPU of receive frame-sync errors, you
can set a special receive interrupt mode with the RINTM bits of SPCR1.
When RINTM = 11b, the McBSP sends a receive interrupt (RINT) request
to the CPU each time that RSYNCERR is set.
4.3.2 Example of an Unexpected Receive Frame-Sync Pulse
4 shows an unexpected receive frame-sync pulse during normal
operation of the serial port, with time intervals between data packets. When
the unexpected frame-sync pulse occurs, the RSYNCERR bit is set, the
reception of data B is aborted, and the reception of data C begins. In addition,
if RINTM = 11b, the McBSP sends a receive interrupt (RINT) request to the
CPU.
Содержание TMS320VC5509
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