Serial Port Exception Conditions; Receive Overrun: Rfull; Data Packing At Maximum Frame Frequency With (R/X)Fig - Texas Instruments TMS320C6000 DSP Reference Manual

Serial Port Exception Conditions

Figure 5-8. Data Packing at Maximum Frame Frequency With (R/X)FIG = 1
CLKR
FSR
DR
CLKX
FSX
DX
5.5 Serial Port Exception Conditions
There are five serial port events that can constitute a system error:
• Receive overrun (RFULL = 1)
• Unexpected receive frame synchronization (RSYNCERR = 1)
• Transmit data overwrite
• Transmit empty (XEMPTY = 0)
• Unexpected transmit frame synchronization (XSYNCERR = 1)
5.5.1

Receive Overrun: RFULL

RFULL = 1 in SPCR indicates that the receiver has experienced overrun and is in an error condition.
RFULL is set when the following conditions are met:
• DRR has not been read since the last RBR-to-DRR transfer.
• RBR is full and an RBR-to-DRR copy has not occurred.
• RSR is full and an RSR-to-RBR transfer has not occurred.
The data arriving on DR is continuously shifted into RSR. Once a complete element is shifted into RSR,
an RSR-to-RBR transfer can occur only if an RBR-to-DRR copy is complete. Therefore, if DRR has not
been read by the CPU or the DMA controller since the last RBR-to-DRR transfer (RRDY = 1), an
RBR-to-DRR copy does not take place until RRDY = 0. This prevents an RSR-to-RBR copy. New data
arriving on the DR pin is shifted into RSR, and the previous contents of RSR is lost. After the receiver
starts running from reset, a minimum of three elements must be received before RFULL can be set,
because there was no last RBR-to-DRR transfer before the first element.
This data loss can be avoided if DRR is read no later than two and a half CLKR cycles before the end of
the third element (data C) in RSR, as shown in
Either of the following events clears the RFULL bit and allows subsequent transfers to be read properly:
• Reading DRR
• Resetting the receiver (RRST = 0) or the device
Another frame synchronization is required to restart the receiver.
44 McBSP Standard Operation
Element 1
Frame ignored Frame ignored
Frame ignored Frame ignored
Figure 5-10.
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Frame ignored
RBR-to-DRR copy
Frame ignored
DXR-to-XSR copy
SPRU580E – December 2005