1. 1. guide

1.1 Purpose

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

1.2 Overview

DMA is provided on two devices, the CPU and the SCU. The library supports both.
The function provided high-level and low-level libraries for each of the CPU and SCU.

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

• High-level function <BR> We have prepared a basic function that can execute byte, word, longword transfer, etc. with simple settings.

• Low-level function <BR> We have prepared a function that allows you to make detailed settings such as state acquisition, mode setting, and interrupts.

The main differences between CPU and SCU applications are described below (see the hardware manual for details).

• CPU
  This is not possible with SCU, so it is effective for forwarding between the same buses (between work RAMs, etc.).

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

1.3 Precautions for use

• Find out the source and destination access unit you want to use for the transfer, and then use the appropriate function. For the access unit, see each hardware manual.

• For high-level DMA transfers, the destination area cache is purged after the transfer when the destination is as follows:
  [Condition] When the destination is work RAM.
  [Reason] As a premise, the RAM read using the cache is the work RAM.
  The above is assumed because there is little need to use the cache to read anything other than work RAM.

• Burst mode is not available on the CPU.

• When using low-level SCU DMA, allow the DMA end interrupt mask register corresponding to the channel to be used.

1.4 Calling sequence

The following is the calling sequence for DMA transfers.

#define SCLA_CFRAME ((void *) 0x5e60000) / * VDP2 VRAM scroll factor address * /
#define K_NUM (424) / * Scroll coefficient data size * /
Uint32 scl_k_data [512]; / * Scroll coefficient data area of work RAM * /
...
void copyToData ()
{
     DMA_ScuCopyMem (SCLA_CFRAME, scl_k_data, K_NUM);
/ * Data transfer from work RAM to VDP2 VRAM * /
     ...
     if (DMA_ScuResult () == DMA_SCU_BUSY) {/ * Check the end of DMA_ScuCopyMem () * /
     ...
     }
}