Fast Ethernet Controller (FEC)
16-18
Freescale Semiconductor
MCF51CN128 Reference Manual, Rev. 6
16.4.16 Descriptor Group Lower Address Register (GALR)
GALR contains the lower 32 bits of the 64-bit hash table used in the address recognition process for
receive frames with a multicast address. You must initialize this register.
16.4.17 Transmit FIFO Watermark Register (TFWR)
The TFWR controls the amount of data required in the transmit FIFO before transmission of a frame can
begin. This allows you to minimize transmit latency (TFWR = 00 or 01) or allow for larger bus access
latency (TFWR = 11) due to contention for the system bus. Setting the watermark to a high value
minimizes the risk of transmit FIFO underrun due to contention for the system bus. The byte counts
associated with the TFWR field may need to be modified to match a given system requirement (worst case
bus access latency by the transmit data DMA channel).
Table 16-18. GAUR Field Descriptions
Field
Description
31–0
GADDR1
The GADDR1 register contains the upper 32 bits of the 64-bit hash table used in the address recognition process for
receive frames with a multicast address. Bit 31 of GADDR1 contains hash index bit 63. Bit 0 of GADDR1 contains
hash index bit 32.
Offset: 0x124
Access: User read/write
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R
GADDR2
W
Reset — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —
Figure 16-17. Descriptor Group Lower Address Register (GALR)
Table 16-19. GALR Field Descriptions
Field
Description
31–0
GADDR2
The GADDR2 register contains the lower 32 bits of the 64-bit hash table used in the address recognition process for
receive frames with a multicast address. Bit 31 of GADDR2 contains hash index bit 31. Bit 0 of GADDR2 contains
hash index bit 0.
Offset: 0x144
Access: User read/write
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
TFWR
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0
0
Figure 16-18. Transmit FIFO Watermark Register (TFWR)