CLKX
DX
FSX
A1
B7
B6
B5
B4
B3
B2
B1
B0
A0
XSYNCERR
mcbsp-040
Unexpected frame synchronization
Public Version
McBSP Functional Description
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the MPU/IVA2.2 subsystem or the sDMA controller before internal FSX goes active high, a valid
XB-to-XSR transfer occurs. This allows for the first word of the first frame to be valid even before the
transmit frame-synchronization pulse is generated or detected. Alternatively, if a transmit
frame-synchronization pulse is detected before McBSPi.
is loaded, zeros are output
on mcbspi_dx.
The McBSPi.
[11] XUNDFLSTAT bit indicates a real underflow condition, in
which the frame is corrupted due to lack of data availability during transmit process. According to the
McBSPi.
register settings this condition can generate the McBSPi_IRQ line
to be asserted low. Writing 1 to the corresponding bit in McBSPi.
register
clears the interrupt.
21.4.4.6 Unexpected Transmit Frame-sync Pulse
21.4.4.6.1 Possible Responses to Transmit Frame-sync Pulses
If a frame-synchronization pulse starts the transfer of a new frame before the current frame is fully
transmitted, this pulse is treated as an unexpected frame-synchronization pulse, and the transmitter sets
the transmit frame-synchronization error bit McBSPi.
[7] XSYNCERR (and
the legacy McBSPi.
[3] XSYNCERR bit).
According to the McBSPi.
register settings, this condition can generate the
McBSPi_IRQ line to be asserted low. Writing 1 to the corresponding bit in status register clears the
interrupt.
Using the legacy mode, McBSPi.
[3] XSYNCERR bit can be cleared only by a
transmitter reset or by a write of 0 to this bit. If you want the McBSP module to notify the MPU/IVA2.2
subsystem of frame-synchronization errors, you can set a special transmit interrupt mode with the
McBSPi.
[5:4] XINTM field. When XINTM=0b11, the McBSP module sends a
transmit interrupt request to the MPU/IVA2.2 subsystem each time that XSYNCERR is set.
21.4.4.6.2 Example of Unexpected Transmit Frame-Synchronization Pulse
shows an unexpected transmit frame-synchronization pulse during normal operation of the
serial port with intervals between the data packets.
NOTE:
The unexpected transmit frame-synchronization pulse does not influence the data transmit
process, being ignored by the data transmit state-machine.
Figure 21-45. Unexpected Frame-sync Pulse During a McBSP Transmission
21.4.4.6.3 Preventing Unexpected Transmit Frame-sync Pulses
Each frame transfer can be delayed by 0, 1, or 2 CLKX cycles, depending on the value in the
McBSPi.
[1:0] XDATDLY field. For each possible data delay,
shows
when a new frame-synchronization pulse on FSX can safely occur relative to the last bit of the current
frame.
3112
Multi-Channel Buffered Serial Port
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated