Programming Model

Field

Reset

R/W

Field

Reset

R/W Address

31

16

GADDR2

Uninitialized

R/W

15

0

GADDR2

Uninitialized

R/W

IPSBAR + 0x1124

Figure 17-20. Descriptor Group Lower Address Register (GALR)

Table 17-29. GALR Field Descriptions

Bits

Name

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.

 

 

 

17.5.4.18 FIFO Transmit FIFO Watermark Register (TFWR)

The TFWR is a 2-bit read/write register programmed by the user to control the amount of data required in the transmit FIFO before transmission of a frame can begin. This allows the user to minimize transmit latency (TFWR = 0x) or allow for larger bus access latency (TFWR = 11) due to contention for the system bus. Setting the watermark to a high value will minimize 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).

Field

Reset

R/W

Field

Reset

R/W Address

31

16

0000_0000_0000_0000

R/W

15

2

1

0

X_WMRK

0000_0000_0000_0000

R/W

IPSBAR + 0x1144

Figure 17-21. FIFO Transmit FIFO Watermark Register (TFWR)

17-40

MCF5282 User’s Manual

MOTOROLA

Page 396
Image 396
Motorola MCF5282, MCF5281 user manual Fifo Transmit Fifo Watermark Register Tfwr, GADDR2, Xwmrk