Chapter 9: DMA Controller
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
9-3
DMA0
DMA7
DMA6
DMA5
DMA4
DMA3
DMA2
DMA1
Figure 9-1 Round-Robin Priority Scheme
9.1.2
Source and Destination
The DMAC conducts data transfers within memory or between a memory and an I/O device.
The device at the data transfer origin is called a
source
device, and the device at the data
transfer destination is called a
destination
device. Memory and I/O devices can be
designated as a source device or a destination device. The DMAC can transfer data from
the C790 bus memory to any other memory or I/O device. The difference between a
memory and an I/O device is the access method to the device. When the DMAC accesses
an I/O device, it always uses the same fixed address. On the other hand, when the DMAC
accesses memory, it either increments or decrements the address after each access.
9.1.3 Block
Transfers
In the block mode, each hardware or software DMA request sends a request to the DMAC
to transfer a block of data. The size of the block of data in bytes is in the current byte count
register (BCR0 – BCR7).
When a block mode DMA channel is granted access, the actual transfer takes place in two
steps.
1. The DMAC arbitrates for the source bus, transfers the data from the source device to the
FIFO when granted the source bus, and aligns the data before they are written to the
FIFO.
2. The DMAC now arbitrates for bus ownership on the destination bus. When the DMAC is
granted the destination bus, it transfers the block of data from the FIFO to the
destination device.
During the block mode transfer, the DMAC ignores other DMA requests, and there is no
interference from other DMA channels. At the end of the block transfer, the DMAC
generates an interrupt to the C790.
The transfer can be from memory to an I/O device, from an I/O device to memory, or from
memory to memory.
Содержание TMPR7901
Страница 1: ...TX System RISC TX79 Family TMPR7901 Symmetric 2 way superscalar 64 bit CPU ...
Страница 14: ...Handling Precautions ...
Страница 15: ......
Страница 17: ...1 Using Toshiba Semiconductors Safely 1 2 ...
Страница 41: ...4 Precautions and Usage Considerations 4 2 ...
Страница 42: ...TX7901 User s Manual Rev 6 30T November 2001 DOCUMENT NUMBER M 99 00004 07 ...
Страница 43: ......
Страница 259: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 1 13 Removed ...
Страница 260: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 2 ...