4. DMA
118
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
4.3
Direct Mode DMA Operation
In Direct mode, the contents for all of a DMA channel registers are directly programmed into
PowerSpan II before every DMA operation (see
). This results in higher software overhead
than in Linked-List mode since PowerSpan II register accesses are required for every DMA block
transfer.
4.3.1
Initializing a Direct Mode Operation
The GO bit in the
“DMA x General Control and Status Register” on page 314
is used when the
following conditions are met:
•
The CHAIN bit is zero which indicates a Direct mode operation
•
All status bits in the DMA General Control and Status Register are cleared, including: P1_ERR,
P2_ERR, PB_ERR, STOP, HALT, DONE
The CHAIN bit and status bits can be properly configured on the same register write which sets the GO
bit.
The DMA channel delivers data from the source port to the destination port until:
•
DMA is stopped by setting the STOP_REQ bit
•
DMA encounters an error on one of the buses
•
transfer byte count decrements to zero
When the Direct mode operation completes the programmed transfer, PowerSpan II sets the DONE bit.
The operation completes when the transfer byte count decrements to zero. The operation of a Direct
mode operation is illustrated in