Freescale Semiconductor MCF5480 User Manual
Page 968
MCF548x Reference Manual, Rev. 3
30-38
Freescale Semiconductor
30.3.3.30 FEC Transmit FIFO Last Write Frame Pointer Register (FECTLWFP)
The last read frame pointer (LWFP) is a FIFO-maintained pointer that indicates the location of the next
byte after the last frame that has been completely written. If no frames have been written into the FIFO,
the register indicates the first byte location in the FIFO(the reset state).The LWFP updates on FIFO write
data accesses which create a frame boundary, whether that be by setting the WFR bit in the FIFO Control
Register, or by feeding a frame bit in on the appropriate bus. The LWFP can be read and written for debug
purposes. For the frame discard function, the LWFP divides the valid data region of the FIFO (the area
in-between the read and write pointers) into framed and unframed data. Data between the LWFP and write
pointer constitutes an incomplete frame, while data between the read pointer and the LWFP has been
received as whole frames. When FECTFCR[FRMEN] is not set, then this pointer has no meaning. The last
written frame pointer is reset to zero, and non-functional bits of this pointer will always remain zero.
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
R
0
0
0
0
0
0
LRFP
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Reg
Addr
MBAR + 0x91B0 (FEC0), 0x99B0 (FEC1)
Figure 30-32. FEC Transmit FIFO Last Write Frame Pointer Register (FECTLRFP)
Table 30-36. FECTLRFP Field Descriptions
Bits
Name
Descriptions
31–10
—
Reserved, should be cleared.
9–0
LRFP
Last read frame pointer. This pointer indicates the location of the next byte after the last frame that
has been completely read. If no frames have been read out of the FIFO, LRFP indicates the first
byte location in the FIFO( the reset state).