Rainbow Electronics DS3131 - Manual (Page 89)

DS3131
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Figure 9-8. Receive Done-Queue Structure
Once the receive DMA is activated (through the RDE control bit in the master configuration register, see
Section
5 ), it can begin writing data to the done queue. It knows where to write data into the done queue
by reading the write pointer and adding it to the base address to obtain the actual 32-bit address. Once
the DMA has written to the done queue, it increments the write pointer by one dword. A check must be
made to ensure the incremented address does not exceed the receive done queue end address. If the
incremented address exceeds this address, the incremented write pointer is set equal to 0000h (i.e., the
base address).
Status Bits/Interrupts
On writes to the done queue by the DMA, the DMA sets the status bit for the receive DMA done-queue
write (RDQW) in the status register for DMA (SDMA). The host can configure the DMA to either set
this status bit on each write to the done queue or only after multiple (from 2 to 128) writes. The host
controls this by setting the RDQT0 to RDQT2 bits in the receive DMA queues control (RDMAQ)
register. See the description of the RDMAQ register at the end of Section
9.2.4 for more details. The
DMA also checks the receive done-queue host read pointer to ensure an overflow does not occur. If this
does occur, the DMA then sets the status bit for the receive DMA done-queue write error (RDQWE) in
the status register for DMA (SDMA), and it does not write to the done queue nor does it increment the
write pointer. In such a scenario, packets can be lost and unrecoverable. Each of the status bits can also
(if enabled) cause a hardware interrupt to occur. See Section
5 for more details.
Base + 00h
Base + 04h
Base + 08h
Base + 0Ch
Base + 10h
Base + 14h
Base + End Address
Done-Queue DMA Write Pointer
Done-Queue Host Read Pointer
Maximum of 65,536
Done-Queue Descriptors
DMA Readied
Done-Queue Descriptor
DMA Readied
Done-Queue Descriptor
DMA Readied
Done-Queue Descriptor
DMA Readied
Done-Queue Descriptor
Host Processed
Done-Queue Descriptor
Host Processed
Done-Queue Descriptor
Host Processed
Done-Queue Descriptor