Ethernet MAC Controller
LH79524/LH79525 User’s Guide
6-28
Version 1.0
6.3.2.6 Transmit Buffer Queue Pointer (TXBQP)
This register points to the entry in the transmit buffer queue (descriptor list) currently being
used. It is written with the start location of the transmit buffer descriptor list. The lower order
bits increment as buffers are used up and wrap to their original values after either 1,024
buffers, or when the wrap bit of the entry is set. This register can only be written when
transmit is inactive, that is, when TXSTATUS:TXGO is LOW.
As transmit buffer reads consist of a burst of two words, it is recommended that bit 2 is
always written with zero. This is to prevent a burst from crossing a 1KB boundary, in vio-
lation of Section 3.6 of the AMBA specification
.
Table 6-16. TXBQP Register
BIT
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
FIELD
TXBQP
RESET
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
TYPE
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
BIT
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
FIELD
TXBQP
///
RESET
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
TYPE
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
RO
ADDR
0xFF 0x1C
Table 6-17. TXBQP Fields
BITS
NAME
FUNCTION
31:2
TXBQP
Transmit Buffer Queue Pointer
Write the address of the start of the transmit
queue. Reads as a pointer to the first buffer of the frame being transmitted or
about to be transmitted.
1:0
///
Reserved
Reading returns 0. Write the reset value.