Chapter 12: 10/100 IEEE802.3 Media Access Controller
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
12-2
12.1.1 C790 and MAC DMA
The MAC provides a powerful host system interface through its own DMA. It manages the
shared memory structures automatically through the frame Descriptors and buffers.
Figure 12-2 MAC Memory Sharing with C790
The MAC’s DMA has one channel to transfer data between memory and the MAC. There
are four tasks for the DMA:
1. Get a frame Descriptor
2. Update the status in a frame Descriptor
3. Transfer transmit frame data from memory to the Transmit FIFO (TxFIFO)
4. Transfer received frame data from the Receive FIFO (RxFIFO) to memory.
The priority for each task depends on whether the RxFIFO is close to being full or the
TxFIFO is close to empty. The software can also select the priority.
The DMA provides logic for controlling the G-Bus master read and write operations. The
functions controlled include:
•
Burst size control
•
Transmit/Receive threshold control
•
Automatic Frame Descriptor polling
•
Frame Descriptor status update
TxFrm
Descriptor 0
TxFrm
Descriptor n
RxFrm
Descriptor 0
RxFrm
Descriptor n
Buffer 0
Buffer 1
Buffer x
Buffer 0
Buffer 1
Buffer y
Initial Command
Interrupt (Error)
MAC
C790
Shared Memory
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Summary of Contents for TMPR7901
Page 1: ...TX System RISC TX79 Family TMPR7901 Symmetric 2 way superscalar 64 bit CPU ...
Page 14: ...Handling Precautions ...
Page 15: ......
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 ...
Page 43: ......
Page 259: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 1 13 Removed ...
Page 260: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 2 ...