NXP Semiconductors UM10237 - page 243

UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 243 o f 792
NXP Semiconductors UM10237
Chapter 11: LPC24XX Ethernet
The StatusInfo word contains flags returned by the MAC and flags generated by the
receive datapath reflecting the status of the reception. Table 11–237 lists the bit definitions
in the StatusInfo word.
[1] The EMAC doesn't distinguish the frame type and frame length, so, e.g. when the IP(0x8000) or
ARP(0x0806) packets are received, it compares the frame type with the max length and gives the "Range"
error. In fact, this bit is not an error indication, but simply a statement by the chip regarding the status of the
received frame.
For multi-fragment frames, the value of the AlignmentError, RangeError, LengthError,
SymbolError and CRCError bits in all but the last fragment in the frame will be 0; likewise
the value of the FailFilter, Multicast, Broadcast, VLAN and ControlFrame bits is undefined.
The status of the last fragment in the frame will copy the value for these bits from the
MAC. All fragment statuses will have valid LastFrag, RxSize, Error, Overrun and
NoDescriptor bits.
Table 237. Rec eive status information word
Bit Symbol Description
10:0 RxSize The size in bytes of the actual data transferred into one fragment buffer. In
other words, this is the size of the frame or fragment as actually written by
the DMA manager for one descriptor. This may be different from the Size
bits of the Control field in the descriptor that indicate the size of the buffer
allocated by the device driver. Size is -1 encoded e.g. if the buffer has
8 bytes the RxSize value will be 7.
17:11 - Unused
18 ControlFrame Indicates this is a control frame for flow control, either a pause frame or a
frame with an unsupported opcode.
19 VLAN Indicates a VLAN frame.
20 FailFilter Indicates this frame has failed the Rx filter. These frames will not normally
pass to memory. But due to the limitation of the size of the buffer, part of
this frame may already be passed to memory. Once the frame is found to
have failed the Rx filter, the remainder of the frame will be discarded
without being passed to the memory. However, if the PassRxFilter bit in
the Command register is set, the whole frame will be passed to memory.
21 Multicast Set when a multicast frame is received.
22 Broadcast Set when a broadcast frame is received.
23 CRCError The received frame had a CRC error.
24 SymbolError The PHY reports a bit error over the MII during reception.
25 LengthError The frame length field value in the frame specifies a valid length, but does
not match the actual data length.
26 RangeError[1] The received packet exceeds the maximum packet size.
27 AlignmentError An alignment error is flagged when dribble bits are detected and also a
CRC error is detected. This is in accordance with IEEE std. 802.3/clause
4.3.2.
28 Overrun Receive overrun. The adapter can not accept the data stream.
29 NoDescriptor No new Rx descripto r is avai lable and the frame is too long for the buffer
size in the current receive descriptor.
30 LastFlag When set to 1, indicates this descriptor is for the last fragment of a frame.
If the frame consists of a single fragment, this bit is also set to 1.
31 Error An error occurred during reception of this frame. This is a logical OR of
AlignmentError, RangeError, LengthError, SymbolError, CRCError, and
Overrun.