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11.1 Introduction
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 their bandwidth moving data, whether it is
from off-chip memory to on-chip memory, or from a peripheral such as an analog-to-digital converter (ADC) to
RAM, or even 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 reference guide
has the ability to free up CPU bandwidth and rearrange the data into a pattern for more streamlined processing.
11.2 DMA Overview
The DMA module is an event-based machine, meaning it requires a peripheral interrupt trigger to start a DMA
transfer. Although it can be made into a periodic time-driven machine by configuring a timer as the interrupt
trigger source, there is no mechanism within the module itself to start memory transfers periodically. The
interrupt trigger source for each of the six DMA channels can be configured separately and each channel
contains its own independent PIE interrupt to let the CPU know when a DMA transfers has either started or
completed. Five of the six channels are exactly the same, while Channel 1 has one additional feature: 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. It is this address control logic that 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, along
with others will be discussed in detail in this document.
• Six channels with independent PIE interrupts
• Peripheral interrupt trigger sources
– ADC interrupts 1 and 2
– Multichannel buffered serial port transmit and receive
– XINT1-3
– CPU Timers
– ePWM2-7 ADCSOCA and ADSOCB signals
– USB endpoints 1-3 transmit and receive
– Software
• Data sources/destinations:
– L5-L8 32K x 16 SARAM
– ADC memory bus mapped result registers
– McBSP transmit and receive buffers
– ePWM1-8 / HRPWM1-8
The DMA module can access all the PWM modules as shown in
. However, only 6 out of 8 PWM
modules (ePWM2-ePWM7) can trigger DMA using PERINTSEL.
• Word Size: 16-bit or 32-bit (McBSP limited to 16-bit)
• Throughput: 4 cycles/word (5 cycles/word for McBSP reads)
Direct Memory Access (DMA) Module
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TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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