A1
B2
B3
B4
B5
B6
B7
B4
B5
B6
XSYNCERR
XRDY
DX
FSX
B1
B0
B7
A0
CLKX
Unexpected frame synchronization
Write of DXR (C)
DXR-to-XSR (C)
Write of DXR (D)
DXR-to-XSR copy (B)
Preliminary
Architecture
www.ti.com
The XUNDFLSTAT in IRQSTATUS register indicates a real underflow condition, in which the frame is
corrupted due to lack of data availability during transmit process. According to the IRQENABLE register
settings this condition can generate the COMMONIRQ line to be asserted low. Writing 1 to the
corresponding bit in status register will clear the interrupt.
11.2.3.5 Unexpected Transmit Frame-Sync Pulse
11.2.3.5.1 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 XSYNCERR in IRQSTATUS (and the legacy
XSYNCERR bit in SPCR2_REG[3]) register.
According to the IRQENABLE register settings this condition can generate the COMMONIRQ line to be
asserted low. Writing 1 to the corresponding bit in status register will clear the interrupt.
Using the legacy mode, XSYNCERR bit in SPCR2_REG 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–synchronization errors, you
can set a special transmit interrupt mode with the SPCR2_REG[5:4] register XINTM bits. When XINTM
= 11b, the McBSP sends a transmit interrupt (XINT) request to the CPU each time that XSYNCERR is
set.
11.2.3.5.2 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 that the unexpected transmit frame–synchronization pulse does not influence the data transmit
process, being ignored by the data transmit state machine.
Figure 11-17. Unexpected Frame-Sync Pulse During a McBSP Transmission
11.2.3.5.3 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
XCR2_REG[1:0] register XDATDLY bits. 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.
1142
Multichannel Buffered Serial Port (McBSP)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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