Information

Enhanced Three-Speed Ethernet Controllers
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
Freescale Semiconductor 16-69
16.5.3.5.4 Half-Duplex Register (HAFDUP)
The HAFDUP register is written by the user. Figure 16-38 describes the HAFDUP register.
Table 16-42 describes the fields of the HAFDUP register.
Offset eTSEC1:0x2_450C; eTSEC2:0x2_550C Access: Read/Write
0781112131415
R
—
Alternate BEB
Tr unc at io n
Alt BEB BP No BackOff No BackOff Excess Defer
W
Reset 0 0 0 0 00 0 01010 0 0 0 1
16 19 20 21 22 31
R
Retransmission Maximum — Collision Window
W
Reset 1 1 1 1 00 0 00011 0 1 1 1
Figure 16-38. Half-Duplex Register Definition
Table 16-42. HAFDUP Field Descriptions
Bits Name Description
0–7 — Reserved
8–11 Alternate BEB
Truncation
This field is used while ALTERNATE BINARY EXPONENTIAL BACKOFF ENABLE is set. The
value programmed is substituted for the Ethernet standard value of ten. Its default is 0xA.
12 Alt BEB Alternate binary exponential backoff. This bit is cleared by default.
0 The Tx MAC follows the standard binary exponential back off rule.
1 The Tx MAC uses the ALTERNATE BINARY EXPONENTIAL BACKOFF TRUNCATION setting
instead of the 802.3 standard tenth collision. The standard specifies that any collision after the
tenth uses one less than 210 as the maximum backoff time.
13 BP No
BackOff
Back pressure no backoff. This bit is cleared by default.
0 The Tx MAC follows the binary exponential back off rule.
1 The Tx MAC immediately re-transmits, following a collision, during back pressure operation.
14 No BackOff No backoff. This bit is cleared by default.
0 The Tx MAC follows the binary exponential back off rule.
1 The Tx MAC immediately re-transmits following a collision.
15 Excess Defer Excessively deferred. This bit is set by default.
0 The Tx MAC aborts the transmission of a packet that is excessively deferred.
1 The Tx MAC allows the transmission of a packet that is excessively deferred.
16–19 Retransmission
Maximum
This is a programmable field specifying the number of retransmission attempts following a collision
before aborting the packet due to excessive collisions. The standard specifies the attempt limit to
be 0xF (15d). Its default value is 0xF.
20–21 — Reserved
22–31 Collision Window This is a programmable field representing the slot time or collision window during which collisions
occur in properly configured networks. Because the collision window starts at the beginning of
transmission, the preamble and SFD are included. Its default of 0x37 (55d) corresponds to the
count of frame bytes at the end of the window.