SPRUHM9H October 2014 – May 2024 TMS320F28075 , TMS320F28075-Q1 , TMS320F28076
The strength of a controller is not measured purely in processor speed, but in total system capabilities. As a part of the equation, any time the CPU bandwidth for a given function can be reduced, the greater the system capabilities. Many times applications spend a significant amount of the bandwidth moving data, whether moving data from off-chip memory to on-chip memory, from a peripheral such as an analog-to-digital converter (ADC) to RAM, or from one peripheral to another. Furthermore, many times this data comes in a format that is not conducive to the optimum processing powers of the CPU. The DMA module described in this chapter has the ability to free up CPU bandwidth and rearrange the data into a pattern for more streamlined processing.
The DMA module is an event-based machine, meaning the DMA module requires a peripheral or software trigger to start a DMA transfer. Although the DMA module can be made into a periodic time-driven machine by configuring a timer as the DMA trigger source, there is no mechanism within the module to start memory transfers periodically. The DMA module has six independent DMA channels that can be configured separately and each channel contains an independent PIE interrupt to let the CPU know when a DMA transfer has either started or completed. Five of the six channels are exactly the same, while Channel 1 has the ability to be configured at a higher priority than the others. At the heart of the DMA is a state machine and tightly coupled address control logic. This address control logic allows for rearrangement of the block of data during the transfer as well as the process of ping-ponging data between buffers. Each of these features is discussed in detail in this chapter.