Achronix Speedster22i 10G/40G/100G Ethernet - Manual (Page 43)

UG029, September 6, 2013 43
Table 22 – Frame Status Word Bits
Bit # Name Description
0 LENGTH_ERROR
Set to ‘1’ if the frame has an invalid length. This can be
either a too long frame (length greater than the value
programmed in register FRM_LENGTH), or a frame which
has a different amount of payload than specified in the
frame's payload length field.
Frames below 64 octets in length are never delivered to the
FIFO interface.
1 CRC_ERROR
Set to ‘1’ if the frame was received with a CRC field that did
not match the CRC calculated by the MAC Core. The frame
is invalid.
2 PHY_ERROR
Set to ‘1’ if the frame was received with an unknown control
character. The frame is invalid.
3 FIFO_OVERFLOW
Set to ‘1’ if a FIFO overflow was detected during frame
reception. The received frame is truncated by the MAC
Core and is invalid.
4 FAULT_SEQ
Set to ‘1’ if a Sequence Error (local or remote fault) has
been received from the PHY during frame reception. The
frame is invalid.
5 STACKED_VLAN
Set to ‘1’ to indicate that the frame is a Stacked VLAN
frame. This information can be used to switch the received
frame to dedicated VLAN frames processing engines.
6 TRANSMIT_ERR
Set to ‘1’ if a transmit error control character (0xFE) has
been received from the line. The frame is invalid.
7 VLAN
Set to ‘1’ to indicate that the frame is a VLAN frame. This
information can be used to switch the received frame to
dedicated VLAN frames processing engines.
23:8 PAYLOAD_LEN
Frame payload length in bytes or type information. The
copied value of the frame's length/type field. For VLAN
frames the value immediately following the 4-octet VLAN
tag is copied.
FIFO Thresholds
The Core implements programmable FIFO thresholds that provide the possibility to
dynamically change the FIFO operation and fixed Almost Full and Almost Empty thresholds
for FIFO overflow / underflow protection.
FIFO Sections Behavior (Watermarks)
The FIFO logic offers to set high- and low-watermarks by setting the configuration registers
RX_FIFO_SECTIONS and TX_FIFO_SECTIONS. The sections are defined in steps of segment
data words (10G: 32-bit, 40G: 128-bit, 100G: 384-bit).

tx/rx_section (section available) defines a low-watermark that is used to assert an
internal signal when this amount of data is available in the FIFO.

tx/rx_section_e (section empty) defines a high-watermark that is used to de-assert an
internal signal when the FIFO is filled to this level and above.