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
mcbsp-039
Public Version
www.ti.com
McBSP Functional Description
Figure 21-44. Proper Positioning of Receive Frame-sync Pulses
21.4.4.4 Underflow in the Receiver
The McBSP module indicates a receiver underflow condition by setting the
McBSPi.
[4] RUNDFLSTAT bit. This error occurs when sDMA controller or
MPU/IVA2.2 subsystem reads data from an empty RB this happens only if the MPU/IVA2.2 subsystem or
sDMA 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 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.
21.4.4.5 Underflow in the Transmitter
The McBSP module indicates a transmitter empty (or underflow) condition by setting the
McBSPi.
[11] XUNDFLSTAT bit. Also the legacy mode
McBSPi.
[2] XEMPTY bit is cleared. Either of the following events activates
XEMPTY bit (XEMPTY = 0):
•
has not been loaded and XB is empty, and all bits of the data word in
the XSR have been shifted out on the mcbspi_dx pin.
•
The transmitter is reset (by forcing McBSPi.
[0] XRST=0, or by an global
reset) and is then restarted.
XEMPTY bit is deactivated (XEMPTY=1) when a new word in McBSPi.
is
transferred to Transmit Buffer (XB). If McBSPi.
[11] FSXM=1 and
McBSPi.
[12] FSGM=0, the transmit frame-sync signal (FSX) is generated when
Transmit Buffer (XB) is not empty. When McBSPi.
[12] FSGM=0,
McBSPi.
[11:0] FPER and McBSPi.
[15:8] 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 mcbspi_dx.
When the transmitter is taken out of reset (McBSPi.
[0] XRST=1), it is in a
transmitter ready state (McBSPi.
[1] XRDY bit =1) and transmitter empty
(McBSPi.
[2] XEMPTY=0) state. If McBSPi.
is loaded by
3111
SWPU177N – December 2009 – Revised November 2010
Multi-Channel Buffered Serial Port
Copyright © 2009–2010, Texas Instruments Incorporated