1. guide

1.1 Purpose

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

1.2 Overview

DMA is provided in two devices: CPU and SCU. The library supports both.
We have prepared high-level and low-level function libraries for CPU and SCU, respectively.

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

• high level functions
  We have provided basic functions that allow you to perform byte, word, and longword transfers with simple settings.

• low level functions
  We have prepared functions that allow detailed settings such as status acquisition, mode settings, and interrupts.

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

• CPU
  This cannot be achieved with SCU, so it is effective for transfers between the same buses (between work RAMs, 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 when performing high-speed transfers.

1.3 Precautions for use

• Check the access units of the source and destination you want to use for transfer, and use the appropriate function. For access units, please refer to each hardware manual.

• In high-level DMA transfers, if the destination meets the following conditions, the cache in the destination area is purged after the transfer.
  [Condition] When the destination is work RAM.
  [Reason] The RAM that is read using the cache is assumed to be 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 for CPUs.

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

1.4 Calling Sequence

The calling sequence for DMA transfer is shown below.

#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);
/*Transfer data from work RAM to VDP2 VRAM */
     ...
     if(DMA_ScuResult() == DMA_SCU_BUSY){ /* Check completion of DMA_ScuCopyMem() */
     ...
     }
}