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DMA library

1. Guide

1.1 Purpose

DMA performs data transfer processing on behalf of the CPU to reduce the load on the CPU. This library provides basic DMA functionality.

1.2 Overview

DMA is prepared for two devices, CPU and SCU. The library supports both.
∙ For the functions of the CPU and SCU, high-level and low-level libraries are prepared.

The contents of the high-level and low-level functions are described below.

  • High-level function
    Basic functions that can execute byte, word, longword transfer, etc. with simple settings are now available.

  • Low-level functions
    Functions that can make detailed settings such as status acquisition, mode setting, and interrupts are provided.

    The main differences in usage between the CPU and SCU are explained below (see the hardware manual for details).

  • CPU
    Since it cannot be realized by SCU, it is effective for transfer between the same buses (between work RAM, etc.)

  • SCU
    Since the CPU can operate in parallel during transfer, it is effective for transfers that do not use CPU_Bus. Since it is faster than the CPU, it is effective for high-speed transfer.

    1.3 Precautions

    • Check the access unit of the source and destination you want to use for transfer, and use the appropriate function. For details on the access unit, see the hardware manual.
    • In high-level DMA transfer, the destination area cache is purged after transfer when the destination is under the following conditions. 
       [Conditions] When the destination is work RAM.
[Reason] RAM to be read using cache is assumed to be work RAM.
      The above is assumed because it is not necessary to read anything other than work RAM using a cache.
    • The burst mode cannot be used with the CPU.

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