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Figure 9-6. Receive Free-Queue Structure
Once the receive DMA is activated (by setting the RDE control bit in the master configuration register,
see Section 5
), it can begin reading data out of the free queue. It knows where to read data out of the free
queue by reading the read pointer and adding it to the base address to obtain the actual 32-bit address.
Once the DMA has read the free queue, it increments the read pointer by two dwords. A check must be
made to ensure the incremented address does not equal or exceed either the receive free-queue small-
buffer start address (in the case of the large buffer circular queue) or the receive free-queue end address
(in the case of the small buffer circular queue). If the incremented address does equal or exceed either of
these addresses, the incremented read pointer is set equal to 0000h.
Base + 00h
Base + 08h
Base + 10h
Base + 18h
Base + 20h
Base + End Address
Free-Queue Large Buffe
Host Write Pointe
Free-Queue Large Buffe
DMA Read Pointe
Maximum of 65,536
Free-Queue Descriptors
DMA Acquired
Free-Queue Descripto
Free-Queue Small Buffe
DMA Read Pointe
Free-Queue Small Buffe
Host Write Pointe
Free-Queue Small Buffe
Start Address
Large
Buffe
Circula
Queue
Small
Buffe
Circula
Queue
Host Readied
Free-Queue Descripto
DMA Acquired
Free-Queue Descripto
DMA Acquired
Free-Queue Descripto
DMA Acquired
Free-Queue Descripto
DMA Acquired
Free-Queue Descripto
DMA Acquired
Free-Queue Descripto
Host Readied
Free-Queue Descripto
Host Readied
Free-Queue Descripto
Host Readied
Free-Queue Descripto
Host Readied
Free Queue Descripto
Host Readied
Free-Queue Descripto
Host Readied
Free-Queue Descripto
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