VR4102 datasheet(271/701 Pages) NEC

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CHAPTER 11 DMAAU (DMA ADDRESS UNIT)

This chapter describes the DMAAU register’s operations and settings.

11.1 GENERAL

The DMAAU register controls the DMA addresses for the AIU and IrDA 4-Mbps communication module (FIR).

The DMA channel used for each unit can set a DMA start address as any half-word address in the space from

0x0000 0000 to 0x01FF FFFE, and is retained in DRAM as a 2-Kbyte block that starts at the address which is

generated by masking the low-order 10 bits of the DMA start address.

After a DMA start address is set to the DMA base address register, the VR4102 performs DMA transfer using the

registers of DMAAU as below.

(1) When the DMA start address is included in the first page of the DMA space

1. The VR4102 starts a DMA transfer after writing the start address to the DMA address register.

2. When the DMA transfer reaches the first page boundary, the VR4102 adds 1 Kbyte to the contents of the DMA

base address register, writes the value to the DMA address register, and continues the DMA transfer.

3. When the DMA transfer reaches the second page boundary, the VR4102 writes the contents of the DMA base

address register to the DMA address register and continues the DMA transfer.

4. The VR4102 repeats 2. and 3. until all the data is transferred.

(2) When the DMA start address is included in the second page of the DMA space

1. The VR4102 starts a DMA transfer after writing the start address to the DMA address register.

2. When the DMA transfer reaches the second page boundary, the VR4102 subtracts 1 Kbyte from the contents

of the DMA base address register, writes the value to the DMA address register, and continues the DMA

transfer.

3. When the DMA transfer reaches the first page boundary, the VR4102 writes the contents of the DMA base

address register to the DMA address register and continues the DMA transfer.

4. The VR4102 repeats 2. and 3. until all the data is transferred.

Figure 11-1. DMA Space Used in DMA Transfers

Second page

First page boundary

Base address

DMA space address

Second page

First page boundary

Base address

DMA space address

(a) When the DMA start address is included

in the first page of the DMA space

(b) When the DMA start address is included

in the second page of the DMA space

Caution

DMA operations are not guaranteed if an address overlaps with another DMA buffer.

VR4102 Datasheet(PDF) 271 Page - NEC