LAN9500 Datasheet, PDF (45/213 Pages) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

LAN950x
Dropping an Ethernet frame is implemented by rewinding the received frame. A write side rewind is implemented by
setting the rx_wr_ptr to be equal to the rx_wr_hd_ptr. Similarly, a read side rewind is implemented by setting the
rx_rd_ptr to be equal to the rx_rd_hd_ptr.
For the case where the frame is dropped due to overflow, the FCT ignores the remainder of the frame. It will not begin
writing into the RX FIFO again until the next frame is received.
In the read direction, the FCT must also support rewinds for the UTX. This is needed for the case where the USB Bulk
Out packet is not successfully received by the Host and needs to be retransmitted.
5.4.1.2 RX Status Format
Table 5-40 illustrates the format of the RX Status Word.
TABLE 5-40: RX STATUS WORD FORMAT
Bits
Description
31
30
29:16
15
14
13
12
11
10
9:8
7
6
5
4
3
2
RESERVED
Filtering Fail
When set, this bit indicates that the associated frame failed the address recognizing filtering.
Frame Length
The size, in bytes, of the corresponding received frame.
Error Status (ES)
When set, this bit indicates that the TLI has reported an error. This bit is the logical OR of bits 11, 7,
6, 1 in this status word.
RESERVED
Broadcast Frame
When set, this bit indicates that the received frame has a Broadcast address.
Length Error (LE)
When set, this bit indicates that the actual length does not match with the length/type field of the
received frame.
Runt Frame
When set, this bit indicates that frame was prematurely terminated before the collision window (64
bytes). Runt frames are passed on to the Host only if the Pass Bad Frames bit MAC_CR Bit [16] is
set.
Multicast Frame
When set, this bit indicates that the received frame has a Multicast address.
RESERVED
Frame Too Long
When set, this bit indicates that the frame length exceeds the maximum Ethernet specification of 1518
bytes. This is only a frame too long indication and will not cause the frame reception to be truncated.
Collision Seen
When set, this bit indicates that the frame has seen a collision after the collision window. This
indicates that a late collision has occurred.
Frame Type
When set, this bit indicates that the frame is an Ethernet-type frame (Length/Type field in the frame
is greater than 1500). When reset, it indicates the incoming frame was an 802.3 type frame. This bit
is not set for Runt frames less than 14 bytes.
Receive Watchdog time-out
When set, this bit indicates that the incoming frame is greater than 2048 bytes through 2560 bytes,
therefore expiring the Receive Watchdog Timer.
MII Error
When set, this bit indicates that a receive error (RX_ER asserted) was detected during frame
reception.
Dribbling Bit
When set, this bit indicates that the frame contained a no-integer multiple of 8 bits. This error is
reported only if the number of dribbling bits in the last byte is 4 in the MII operating mode, or at least
3 in the 10 Mbps operating mode. This bit will not be set when the Collision Seen bit[6] is set. If set
and the CRC error[1] bit is reset, then the frame is considered to be valid.
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DS00001875A-page 45