Texas Instruments TMS320C6201 Reference Manual page 241

Table 8–19. Possible Expansion Bus Arbitration Scenarios
(Internal Bus Arbiter Disabled)
XARB = '0'
Current
External Host
XBOFF
Activity
asserted
NO NONE
YES YES N/A N/A
Current DSP state
DMA request to ex-
pansion Bus IO port
pending
DMA request to ex-
pansion bus IO port,
and auxiliary DMA re-
quests are pending
Aux. DMA request
pending
DMA transfer to ex-
pansion bus IO port
in progress
Aux. DMA transfer in
progress
Aux. DMA transfer in
progress, and DMA
request to expansion
bus IO port pending
Actions Actions
The DSP asserts the XHOLD, and once it gets the ex-
pansion bus the transfer starts.
After the DSP gets the expansion bus the pending
auxiliary DMA request is executed first (since for the
expansion bus, the auxiliary DMA channel always has
priority over the rest of the DMA channels). After the
auxiliary DMA transfer is completed, the DSP will start
the DMA transfer and does not drop the XHOLD be
tween these two transfers.
The DSP asserts the XHOLD, and once it gets the ex-
pansion bus the transfer starts.
XBOFF is ignored if a DMA transfer to the expansion
bus IO port is in progress.
The DSP releases ownership of the expansion bus as
soon as possible. After that, the DSP requests the ex-
pansion bus to complete the transfer interrupted by the
XBOFF.
The DSP stops the current auxiliary DMA transfer in
progress, and starts executing the pending DMA trans-
fer to the expansion bus IO port. After the pending DMA
transfer is completed, the DSP releases the expansion
bus to the external device. Some time afterwards, the
DSP requests the expansion bus to complete the trans-
fer interrupted by the XBOFF.
Expansion Bus Arbitration
Expansion Bus 8-47