External Device Requests The Bus From The Tms320C6202 Using Xboff - Texas Instruments TMS320C6201 Reference Manual

Preventing Deadlocks with Backoff
Figure 8–21. External Device Requests the Bus From the TMS320C6202 Using XBOFF
XHOLD (output)
XHOLDA (input)
XHOLD (input)
XHOLDA (output)
XAS (output)
XW/R (output)
XBLAST (output)
XBOFF (input)
To prevent deadlocks while the 'C6202 is performing a master transfer, the ex-
pansion bus has the XBOFF signal. When asserted, XBOFF suspends the
current access and causes the 'C6202 to release ownership of the expansion
bus. Figure 8–21 is timing diagram for the XBOFF signal.
The backoff is only recognized during active master transfers when XRDY
indicates a not ready status and:
1) The external device is requesting the expansion bus (XHOLD = 1), when
the internal bus arbiter is enabled (XARB = 1)
or
2) The DSP is the expansion bus master (XHOLD = 1 and XHOLDA = 1), and
the internal bus arbiter is disabled (XARB = 0).
The backoff request is not serviced until all current master transfers are
completed internally. This allows read data to be flushed out of the pipeline.
The XBOFF signal is not recognized during I/O port transfers.
1
XCLKIN
XD[31:0]
AD
XRDY
2 3 4 5 6
Expansion Bus Host Port Operation
7 8
AD D0 D1 D2
Expansion Bus
D3
8-33