CLKR
DR
FSR
For 0-bit delay:
Next frame-sync pulse
here or later is OK.
For 1-bit delay:
Next frame-sync pulse
here or later is OK.
For 2-bit delay:
Next frame-sync pulse
here or later is OK.
Last bit of
current frame
Earliest possible time
to begin transfer of
next frame
Preliminary
www.ti.com
Architecture
11.2.3.2.3 Preventing Unexpected Receive Frame-Sync Pulses
Each frame transfer can be delayed by 0, 1, or 2 CLKR cycles, depending on the value of the
RCR2_REG[1:0] RDATDLY bits. For each possible data delay,
shows when a new
frame–synchronization pulse on FSR can safely occur relative to the last bit of the current frame.
Figure 11-16. Proper Positioning of Receive Frame-Sync Pulses
11.2.3.3 Underflow in the Receiver
The McBSP indicates a receiver underflow condition by setting the RUNDFLSTAT bit in IRQSTATUS
register. This error occurs when DMA controller or CPU reads data from an empty receive buffer (this
may happen only if the CPU or DMA controller does not respect the DMA length, does not wait for DMA
request or does not check the buffer status before reading data. 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.
11.2.3.4 Underflow in the Transmitter
The McBSP indicates a transmitter empty (or underflow) condition by setting the XUNDFLSTAT bit in
IRQSTATUS register. Also the legacy mode XEMPTY bit in SPCR2_REG[2] register is cleared. Either
of the following events activates XEMPTY (XEMPTY = 0):
•
DXR_REG has not been loaded and transmit buffer is empty, and all bits of the data word in the
XSR have been shifted out on the McBSP.DX pin.
•
The transmitter is reset (by forcing XRST = 0 in SPCR2_REG[0] register, or by an Global reset) and
is then restarted.
XEMPTY is deactivated (XEMPTY = 1) when a new word in DXR_REG is transferred to XB. If FSXM =
1 in PCR_REG[11] and FSGM = 0 in SRGR2_REG[12], the transmit frame-sync signal (FSX) is
generated when transmit buffer is not empty. When FSGM = 0, FPER and FWID are used to determine
the frame synchronization period and width (external FSX is gated by the buffer empty condition).
Otherwise, the transmitter waits for the next frame–synchronization pulse before sending out the next
frame on McBSP.DX.
When the transmitter is taken out of reset (XRST = 1), it is in a transmitter ready state (SPCR2_REG[1]
register XRDY bit = 1) and transmitter empty (XEMPTY = 0) state. If DXR_REG is loaded by the CPU
or the DMA 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 DXR_REG is loaded, zeros are output on McBSP.DX.
1141
SPRUGX9 – 15 April 2011
Multichannel Buffered Serial Port (McBSP)
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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