DISK DMA CHANNEL CONTROL
Data is normally transferred to the disk by direct memory access (DMA). The disk DMA is
controlled by four items:
o Pointer to the area into which or from which the data is to be moved
o Length of data to be moved by DMA
o Direction of data transfer (read/write)
o DMA enable
DSKPTH - POINTER TO DATA
You specify the 32-bit-wide address from which or to which the data is to be transferred.
The lowest bit of the address must be zero, and the buffer must be in CHIP memory. The
value must be written as a single long word to the DSKPTH register ($DFF020).
DSKLEN - LENGTH, DIRECTION, DMA ENABLE
All of the control bits relating to this topic are contained in a write-only register, called
DSKLEN:
Table 8-6: DSKLEN Register ($DFF024)
Bit
Number Name Usage
15 DMAEN Secondary disk DMA enable
14 WRITE Disk write (RAM disk if 1)
13-0 LENGTH Number of words to transfer
- 240 Interface Hardware -
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