Rainbow Electronics DS31256 User Manual
Page 107
DS31256
107 of 181
1) Priority packets are transmitted as soon as the current standard packet (not packet chain) finishes
transmission.
2) All priority packets are transmitted before any more standard packets are transmitted.
3) Priority packets are ordered on a first come, first served basis.
shows an example of a set of priority packets interrupting a set of standard packets. In the
example, the first priority packet chain (shown in column 2) was read by the transmit DMA from the
pending queue while it was transmitting standard packet #1. It waited until standard packet #1 was
complete and then began sending the priority packets. While column 2 was being sent, the priority
packet chains of columns 3 and 4 arrived in the pending queue, so the transmit DMA linked column four
to column three and then waited until all of the priority packets were transmitted before returning to the
standard packet chain in column 1. Note that the packet chain in column 1 was interrupted to transmit the
priority packets. In other words, the transmit DMA did not wait for the complete packet to finish
transmitting, only the current packet.