Freescale Semiconductor MCF5480 User Manual
Page 796
MCF548x Reference Manual, Rev. 3
26-34
Freescale Semiconductor
there are no safeguards to prevent retransmitting data which has been overwritten. When FRMEN in the
PSCRFCR and PSCTFCR is cleared, then this pointer has no meaning. The last read frame pointer is reset
to zero, and non-functional bits of this pointer will always remain zero.
26.3.3.29 Rx and Tx FIFO Last Write Frame Pointer (PSCRLWFPn, PSCTLWFPn)
The last write frame pointer (LWFP) is a FIFO-maintained pointer that indicates the location of the start
of the last frame written into the FIFO. 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 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.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
R
0
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 + 0x867A (PSCRFWP0); 0x877A (PSCRFWP1); 0x887A (PSCRFWP2) ; 0x897A (PSCRFWP3)
and MBAR + 0x869A( PSCTFWP0); 0x879A(PSCTFWP1); 0x889A (PSCTFWP2); 0x899A (PSCTFWP3)
Figure 26-25. TxFIFO (PSCTLRFPn) and RxFIFO (PSCRLRFPn) Last Read Frame Pointer
Table 26-35. PSCRLRFPn / PSCTLRFPn Field Descriptions
Bits
Name
Description
15–9
—
Reserved, should be cleared.
8–0
LRFP
Last read frame pointer. FIFO-maintained pointer which indicates the start of the most recently read
frame or the start of the frame currently in transmission. This register can be read and written for
debug purposes. For the frame retransmit function, the LRFP indicates which point to begin
retransmission of the data frame. There are no safeguards to prevent retransmitting data which has
been overwritten. When the FRMEN bit in the PSCRFCR or PSCTFCR is not set, then this pointer
has no meaning.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
R
0
0
0
0
0
0
0
LWFP
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Reg
Addr
MBAR + 0x867E (PSCRFWP0); 0x877E (PSCRFWP1); 0x887E (PSCRFWP2) ; 0x897E (PSCRFWP3)
and MBAR + 0x869E (PSCTFWP0); 0x879E (PSCTFWP1); 0x889E (PSCTFWP2); 0x899E (PSCTFWP3)
Figure 26-26. TxFIFO (PSCTLWFPn) and RxFIFO (PSCRLWFPn) Last Write Frame Pointer