Table 6-16. Txbqp Register; Table 6-17. Txbqp Fields; Transmit Buffer Queue Pointer (Txbqp) - Sharp LH79524 User Manual

Ethernet MAC Controller

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
BIT
FIELD
RESET
TYPE
BIT
FIELD
RESET
TYPE
ADDR
BITS NAME
31:2 TXBQP
1:0
6-28

Table 6-16. TXBQP Register

31 30 29 28 27
0 0 0 0 0
RW RW RW RW RW
15 14 13 12 11
0 0 0 0 0
RW RW RW RW RW

Table 6-17. TXBQP Fields

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.
/// Reserved Reading returns 0. Write the reset value.
.
26 25 24 23
TXBQP
0 0 0 0
RW RW RW RW
10 9 8 7
TXBQP
0 0 0 0
RW RW RW RW
0xFFFC7000 + 0x1C
FUNCTION
Version 1.0
LH79524/LH79525 User's Guide
22 21 20 19 18
0 0 0 0 0
RW RW RW RW RW
6 5 4 3 2
0 0 0 0 0
RW RW RW RW RW
17 16
0 0
RW RW
1 0
///
0
RO