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 0000000000000000
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 00000000000000 0
TYPE RW RW RW RW RW RW RW RW RW RW RW RW RW RW RO
ADDR 0xFFFC7000 + 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.
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