Unexpected Transmit Frame-Sync Pulse
McBSP Exception/Error Conditions
4-12
SPRU592E
Any one of three cases can occur:
-
Case 1:
Unexpected internal FSX pulses with XFIG = 1 in XCR2.
Unexpected transmit frame-sync pulses are ignored, and the
transmission continues.
-
Case 2:
Normal serial port transmission. Transmission continues
normally because the frame-sync pulse is not unexpected. There are two
possible reasons why a transmit operations might
not
be in progress when
the pulse occurs:
J
This FSX pulse is the first after the transmitter is enabled (XRST = 1).
J
The serial port is in the interpacket intervals. The programmed data
delay for transmission (programmed with the XDATDLY bits of XCR2)
may start during these interpacket intervals before the first bit of the
previous word is transmitted. Therefore, at maximum packet
frequency, frame synchronization can still be received 0 to 2 clock
cycles before the first bit of the synchronized frame.
-
Case 3:
Unexpected transmit frame synchronization with XFIG = 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 transmitted, this pulse is treated as an unexpected
frame-sync pulse, and the transmitter sets the transmit frame-sync error
bit (XSYNCERR) in SPCR2. XSYNCERR
can be cleared only by a
transmitter reset or by a write of 0 to this bit.
If you want the McBSP to notify the CPU of frame-sync errors, you can set
a special transmit interrupt mode with the XINTM bits of SPCR2. When
XINTM = 11b, the McBSP sends a transmit interrupt (XINT) request to the
CPU each time that XSYNCERR is set.
4.6.2 Example of an Unexpected Transmit Frame-Sync Pulse
10 shows an unexpected transmit frame-sync pulse during normal
operation of the serial port, with intervals between the data packets. When the
unexpected frame-sync pulse occurs, the XSYNCERR bit is set and because
no new data has been passed to XSR1 yet, the transmission of data B is
restarted. In addition, if XINTM = 11b, the McBSP sends a transmit interrupt
(XINT) request to the CPU.
Содержание TMS320VC5509
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