Table 6-14. Rxbqp Register; Table 6-15. Rxbqp Fields; Receive Buffer Queue Pointer (Rxbqp) - Sharp LH79524 User Manual

LH79524/LH79525 User's Guide

6.3.2.5 Receive Buffer Queue Pointer (RXBQP)

This register points to the entry in the receive buffer queue (descriptor list) currently being
used. It is written with the start location of the receive 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 bit 1 of the entry is set. Reading this register returns the location of the
descriptor currently being accessed. This value increments as buffers are used.
Software should not use this register for determining where to remove received frames
from the queue as it constantly changes as new frames are received. Software should
instead work its way through the buffer descriptor queue checking the 'used' bits.
Receive buffer writes also comprise bursts of two words, and as with transmit buffer reads,
it is recommended that bit 2 is always written with zero to prevent a burst from crossing a
1KB boundary, in violation of Section 3.6 of the AMBA specification.
BIT
FIELD
RESET
TYPE
BIT
FIELD
RESET
TYPE
ADDR
BITS
31:2
1:0

Table 6-14. RXBQP 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 6-15. RXBQP Fields

NAME
Receive Buffer Queue Pointer Written with the address of the start of
RXBQP
the receive queue, reads as a pointer to the current buffer being used.
/// Reserved Reading returns 0. Write the reset value.
26 25 24 23
RXBQP
0 0 0 0
RW RW RW RW
10 9 8 7
RXBQP
0 0 0 0
RW RW RW RW
0xFFFC7000 + 0x18
FUNCTION
Version 1.0
Ethernet MAC Controller
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 0
RO RO
6-27