
Philips Semiconductors
PNX15xx Series
Volume 1 of 1
Chapter 23: LAN100 — Ethernet Media Access Controller
PNX15XX_SER_3
Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Product data sheet
Rev. 3 — 17 March 2006
23-53
5.6 Transmission Retry
If a packet collision occurs on the Ethernet, it usually takes place during the collision
window spanning the rst 64 bytes of a packet. If collision is detected, the LAN100
will retry the transmission. For this reason, the rst 64 bytes of a packet are buffered
by the LAN100 so that it can be used during the retry. A transmission retry within the
rst 64 bytes in a packet is fully transparent to the application and device driver
software.
When a collision occurs outside of the 64-byte collision window, a LateCollision error
is triggered and the transmission is aborted. After a LateCollision error, the remaining
data in the transmit packet is discarded. The LAN100 sets the Error and LateCollision
bits in the packet’s status elds. The Tx(Rt)Error bit in the IntStatus register is set. If
the corresponding bit in the IntEnable register is set, the Tx(Rt)Error bit in the
IntStatus register will be propagated to the CPU. The device driver software should
catch the interrupt and take appropriate actions.
The RETRANSMISSION_MAXIMUM eld of the CLRT register can be used to
congure the maximum number of retries before aborting the transmission.
5.7 time-stamps
The LAN100 has an internal Time-stamp Counter register, readable by software via
the GlobalTimeStamp register. After reset, the Time-stamp Counter is 0. Every clock
tick of the Time-stamp Clock, the value of the Time-stamp Counter is incremented by
1. After 232–1 clock ticks, the counter wraps back to 0.
The Time-stamp Counter is only reset by asserting a hard reset.
Since the time-stamp is 32 bits in length, the maximum time that can be counted is
(232–1) * Tclk where Tclk is the period of the Time-stamp Clock. For a 100 MHz
Time-stamp Clock this corresponds to a 42 second period. The actual frequency of
the Time-stamp Clock may depend upon the software stack. The maximum
frequency supported by the hardware is 200 MHz.
The value of the Time-stamp Counter is copied in the time-stamp eld of the status
word returned with transmit and receive fragments and packets. The device driver is
able to determine the exact moment of transmission, reception and latencies using
the time-stamp from the status word and the actual time-stamp value in the
GlobalTimeStamp register.
5.8 Transmission modes
5.8.1
Overview
The LAN100 hardware has two transmission datapaths: Tx and TxRt. These
transmission datapaths can be switched in two modes:
Real-time/non-real-time mode: In this mode, the TxRt transmission datapath
handles real-time transmissions, and the Tx datapath handles non-real-time
transmissions.