Chapter 9: DMA Controller
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
9-2
9.1 Modes of Operation
The DMAC has eight independent channels. As channels become active, the Arbiter grants
control to the highest priority channel. The DMAC then begins reading the source data from
the source address and puts the data into the FIFO queue. When the data are ready in the
FIFO queue, the DMAC transfers the data out to the destination address. Figure 9-6 shows
the DMAC operation.
The data FIFO unit contains a FIFO and an aligner. The FIFO can accommodate 16 quad-
words of data. The FIFO gets data from the source device, and the aligner shifts data into
the correct destination alignment depending on the destination address. A request is
generated to the destination device once one of the following results: a non-aligned write
data condition, a FIFO size of more than 8 quad-words, or a “no more read data” condition.
9.1.1
DMA Channel Priority
The DMAC has two types of priority schemes for the DMA channels depending on the
setting of the FRP. If FRP=0, a fixed priority scheme is used. If FRP=1, a round-robin
priority scheme is used.
When fixed priority is programmed, the DMA channel priority corresponds to the FPL[3:0]
field in the CCR registers. FPL[3:0]=0000 is the highest priority whereas FPL[3:0] = 1111 is
the lowest priority. If two DMA channels have the same priority level, the DMA channel
number determines the priority. The DMA channel with the lower channel number is
assigned the higher priority. For example, if channel 1 and channel 5 have the same priority
level 3, channel 1 is assigned a higher priority.
If FRP=1, a round-robin priority scheme is used: the next sequential DMA channel after the
DMA channel that has the token is assigned the highest priority. Upon power-up, DMA
channel 0 has the token. Each time a channel is granted DMA access, the token is
transferred to that channel and the next sequential channel is assigned the highest priority.
For example, if DMA channel 1 has the token originally, then DMA channel 2 has the
highest priority, and DMA channel 3 has the second highest priority. At this time, if DMA
channel 4 submits a request and it is granted, the token is transferred from DMA channel 1
to DMA channel 4. Once the token is transferred, DMA channel 5 has the highest priority,
and DMA channel 6 has the second highest priority. Figure 9-1 illustrates this round-robin
priority scheme described above.
Summary of Contents for TMPR7901
Page 1: ...TX System RISC TX79 Family TMPR7901 Symmetric 2 way superscalar 64 bit CPU ...
Page 14: ...Handling Precautions ...
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Page 17: ...1 Using Toshiba Semiconductors Safely 1 2 ...
Page 41: ...4 Precautions and Usage Considerations 4 2 ...
Page 42: ...TX7901 User s Manual Rev 6 30T November 2001 DOCUMENT NUMBER M 99 00004 07 ...
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