CHAPTER 7 DMA CONTROL UNIT (DCU)
User’s Manual U14272EJ3V0UM
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Priority of each DMA channel is fixed. The channel priority is as follows.
1. AIU Microphone channel
2. AIU Speaker channel
DCU runs at the MBA bus clock (TClock) frequency.
Remark
The DCU contains a 32-bit temporary storage register for each DMA channel. For memory-to-I/O
transfers, the DCU performs a 32-bit memory read from DRAM and stores the read data into the
temporary storage register. The DCU then transfers data from this register to the target I/O device. For
a 16-bit device such as the Speaker channel, the DCU performs two I/O writes to the D/A converter for
each memory read.
During DMA transfers, all DCU registers are write-protected if valid data is present in the temporary
storage registers. Because of this, to start DMA transfers, software must read the register that is written
immediately after the write to confirm that the register has been correctly set.
Содержание VR4181 mPD30181
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