Chapter 11. Ethernet Module
11-35
Buffer Descriptors
The first word of the RxBD contains control and status bits. Its format is detailed below.
Table 11-34. RxBD Field Descriptions
Bits
Name
Description
15
E
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.
14
RO1
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.
13
W
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 R_DES_START.
12
RO2
Receive software ownership. Reserved for use by software. This read/write bit is not
modified by hardware, nor does its value affect hardware.
11
L
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.
10–9
—
Reserved, should be cleared.
8
M
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.
7
BC
Broadcast. Written by the FEC. Will be set if DA is broadcast. (FF-FF-FF-FF-FF-FF)
6
MC
Mulitcast. Written by the FEC. Is set if DA is multicast and not BC.
5
LG
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.
4
NO
Rx non-octet-aligned frame. Written by the FEC. A frame that contained a number of bits
not divisible by 8 was received, and the CRC check that occurred at the preceding byte
boundary generated an error. Valid only if the L-bit is set. If this bit is set, the CR bit is not
set.
3
SH
Short frame. Written by the FEC. A frame length that was less than the minimum defined
for this channel was recognized. The FEC does not support SH and this bit is always
cleared.
2
CR
Rx CRC error. Written by the FEC. Contains a CRC error and is an integral number of
octets in length. Valid only if the L-bit is set.
1
OV
Overrun. Written by the FEC. A receive FIFO overrun occurred during frame reception. If
this bit is set, the other status bits, M, LG, NO, SH, CR, and CL, lose their normal meaning
and are zero. Valid only if the L-bit is set.
0
TR
Truncated receive frame. Written by the FEC. Set if the receive frame is truncated. Frames
greater than or equal to 2048 bytes are truncated.
Содержание DigitalDNA ColdFire MCF5272
Страница 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
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Страница 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Страница 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Страница 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Страница 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Страница 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Страница 338: ...13 44 MCF5272 User s Manual Application Examples ...
Страница 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Страница 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Страница 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Страница 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...
Страница 548: ...INDEX Index 12 MCF5272 User s Manual ...