Rainbow Electronics DS3131 - Manual (Page 104)

DS3131
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descriptor pointer and PV fields in the packet descriptor to 0 to ready them for transmission). The second
option allows the software a cleaner error-recovery technique. See
Figure 9-14 for more details.
Figure 9-14. Transmit DMA Error Recovery Algorithm
Host Actions
The host typically handles the transmit DMA as follows:
1) The host places readied packets into the pending queue.
2) The host either polls (or is interrupted) that some outgoing packets have completed transmission and
that it should read the done queue.
3) If done queue reports that an error was incurred and that a packet was not transmitted, the host must
requeue the packet for transmission.
Transmit DMA Actions
A typical scenario for the transmit DMA is as follows:
1) The transmit DMA constantly reads the pending queue looking for packets that are queued for
transmission.
2) The transmit DMA updates the done queue as packets or data buffers to complete transmission.
3) If an error occurs, the transmit DMA disables the channel and waits for the host to request that the
channel be enabled.
Read Done Queue
Status = 1xx?
No
Data Buffers and
Packet Descriptor
Space Available
for Reuse
Yes
Set CHRST = 1 for
the Next Descriptor
Written to the
Pending Queue
Set the PV and the Next
Pending Descriptor Pointer
Fields to 0 in the Errored
Packet Descriptor
Place the Errored Packet
Descriptor Back into the
Pending Queue for
Retransmission