mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 257

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

MOTOROLA
11.6.1.1 Ethernet Receive Buffer Descriptor (RxBD)
In the RxBD, the user initializes the E and W bits in the first word and the pointer in the
second word. When the buffer has been sent as a DMA, the FEC will modify the E, L, M,
LG, NO, SH, CR, and OV bits and write the length of the used portion of the buffer in the
first word. The M, LG, NO, SH, CR, and OV bits in the first word of the buffer descriptor
are modified by the FEC only when the L bit is set.
The first word of the RxBD contains control and status bits. Its format is detailed below.
+0
+2
+4
+6
10–9
Bits
15
14
13
12
11
8
7
6
5
15
E
Name
RO1
RO2
MC
BC
RO1
LG
W
—
M
E
L
14
Empty. Written by the FEC (= 0) and user (= 1).
0 The data buffer associated with this BD has been filled with received data, or data reception
has been aborted due to an error condition. The status and length fields have been updated as
required.
1 The data buffer associated with this BD is empty, or reception is currently in progress.
Receive software ownership. This field is reserved for use by software. This read/write bit is not
modified by hardware, nor does its value affect hardware.
Wrap. Written by the user.
0 =The next buffer descriptor is found in the consecutive location.
1 =The next buffer descriptor is found at the location defined in ERDSR.
Receive software ownership. Reserved for use by software. This read/write bit is not modified
by hardware, nor does its value affect hardware.
Last in frame. Written by the FEC.
0 =The buffer is not the last in a frame.
1 =The buffer is the last in a frame.
Reserved, should be cleared.
Miss. Written by the FEC. This bit is set by the FEC for frames that were accepted in
promiscuous mode, but were flagged as a miss by the internal address recognition. Thus, while
in promiscuous mode, the user can use the M-bit to quickly determine whether the frame was
destined to this station. Valid only if the L-bit and the PROM bit are set.
0 The frame was received because of an address recognition hit.
1 The frame was received because of promiscuous mode.
Broadcast. Written by the FEC. Will be set if DA is broadcast. (FF-FF-FF-FF-FF-FF)
Mulitcast. Written by the FEC. Is set if DA is multicast and not BC.
Rx frame length violation. Written by the FEC. A frame length greater than MAX_FL was
recognized. Frames exceeding 2047 bytes are truncated to prevent wrapping hardware length
counters. Valid only if the L-bit is set.
13
W
Figure 11-26. Receive Buffer Descriptor (RxBD)
RO2
12
Table 11-34. RxBD Field Descriptions
11
L
Chapter 11. Ethernet Module
10
Rx Data Buffer Pointer A[31–16]
Rx Data Buffer Pointer A[15–0]
—
9
DATA LENGTH
M
8
Description
BC
7
MC
6
LG
5
NO
4
SH
3
Buffer Descriptors
CR
2
OV
1
11-33
TR
0