Texas Instruments TMS320C3x - Manual (Page 452)

DMA Controller
12-73 Peripherals
12.3.9 DMA Initialization/Reconfiguration
You can control the DMA through memory-mapped registers located on the
dedicated peripheral bus. Following is the general procedure for initializing
and/or reconfiguring the DMA:
1) Halt the DMA by clearing the START bits of the DMA global-control register.
You can do this by writing a 0 to the DMA global-control register. The DMA
is halted on RESET.
2) Configure the DMA through the DMA global-control register (with
START = 00), as well as the DMA source, destination, and transfer-
counter registers, if necessary. Refer to Section 12.3.11 on page 12-74
for more information.
3) Start the DMA by setting the START bits of the DMA global-control register
as necessary.
12.3.10 Hints for DMA Programming
The following hints help you to improve your DMA programming and avoid un-
expected results:
- Reset the DMA register before starting it. This clears any previously
latched interrupt that may no longer exist.
- In the event of a CPU-DMA access conflict, the CPU always prevails. Care-
fully allocate the different sections of the program in memory for faster
execution. If a CPU program access conflicts with a DMA access, enabling
the cache helps if the program is located in external memory. DMA on-chip
access happens during the H3 phase.
Note: Expansion and Peripheral Buses
The expansion and peripheral buses cannot be accessed simultaneously
because they are multiplexed into a common port (see Figure 2–1 on
page 2-3). This might increase CPU-DMA access conflicts.
- Ensure that each interrupt is received when you use interrupt synchroniza-
tion; otherwise, the DMA will never complete the block transfer.
- Use read/write synchronization when reading from or writing to serial ports
to guarantee data validity.
The following are indications that the DMA has finished a set of transfers:
- The DINT bit in the IF register is set to 1 (interrupt polling). This requires
that you set the TCINT bit in the DMA control register first. This interrupt-
polling method does not cause any additional CPU-DMA access conflict.