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NXP Semiconductors
PNX15xx/952x Series
Volume 1 of 1
Chapter 23: LAN100 — Ethernet Media Access Controller
PNX15XX_PNX952X_SER_N_4
NXP B.V. 2007. All rights reserved.
Product data sheet
Rev. 4.0 — 03 December 2007
23-725
Real-time/non-real-time example
Figure 10 shows an example of real-time and non-real-time trafc.
In this example initially both transmission queues have three descriptors; the rst
packet in the real-time queue must be transmitted at time-stamp 90, the second
packet must be transmitted at time-stamp 110, and the third packet must be
transmitted at time-stamp 260. The packets in the non-real-time queue will be
transmitted as soon as possible.
In this example the BlockZone register is set to 30 time-stamp cycles.
After the device driver has set up the descriptors at time-stamp 50, the LAN100 starts
transmission. The initial real-time packet need not be transmitted yet, so a packet
from the non-real-time queue is transmitted rst. During transmission of the
non-real-time packet, the time-stamp of the rst real-time packet expires, and the
real-time packet will be transmitted as soon as transmission of the non-real-time
packet completes.
After transmitting the rst real-time packet, the time-stamp of the second real-time
packet expires, and the transmission of the second real-time packet commences as
soon as the rst real-time packet completes transmission.
After sending the second real-time packet, no new packets are sent out, since the
time-stamp is within the range of the block zone of the third real-time packet. As soon
as the Time-stamp Counter passes the packet’s time-stamp, the third real-time packet
is transmitted.
After completing transmission of the third real-time packet, the real-time queue is
empty, and the remaining non-real-time packets are transmitted as soon as possible.
Figure 10: Real-time/non-real-time transmit example
TxRt descriptors
Tx descriptors
Block zone
Expired
LAN
PRT1@90,
Prt2@110,
Prt3@260
PRT2@110,
Prt3@260
P1
P2
P3
P2
P3
P1
Prt1
Prt2
Prt3
P2
P3
Tx clk cycles
0
50
100
150
200
250
300
350
400
450
500