Buffer Descriptors; Data Buffer Descriptors - Freescale Semiconductor MPC8313E Family Reference Manual

Enhanced Three-Speed Ethernet Controllers
Table 15-161. Tx Frame Control Block Description (continued)
Bytes Bits Name
0–1 5 CIP
6 CTU
7 NPH
8–14 —
15 PTP
2–3 0–7 L4OS
8–15 L3OS
4–5 0–15 PHCS
6–7 0–15 VLCTL/
PTP_ID
15.6.7

Buffer Descriptors

The eTSEC buffer descriptor (BD) is modeled after the MPC8260 Fast Ethernet controller BD for ease of
reuse across the PowerQUICC network processor family. Drawing from the MPC8260 FEC BD
programming model, the eTSEC descriptor base registers point to the beginning of BD rings. The eTSEC
BD also expands upon the MPC8260 BD model to accommodate the eTSEC's unique features. However,
the 8-byte data BD format is designed to be compatible with the existing MPC8260 BD model.
15.6.7.1

Data Buffer Descriptors

Data buffers are used in the transmission and reception of Ethernet frames (see
encapsulate all information necessary for the eTSEC to transmit or receive an Ethernet frame. Within each
data BD there is a status field, a data length field, and a data pointer. The BD completely describes an
MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3
15-186
Checksum IP header enable.
0 Do not generate an IP header checksum.
1 Generate an IPv4 header checksum.
Checksum TCP or UDP header enable.
0 Do not generate a TCP or UDP header checksum. RFC 768 advises that UDP packets
not requiring checksum validation should have their checksum field set to zero.
1 Generate a TCP header checksum if IP = 1 and TUP = 1 and UDP = 0.
Disable calculation of TCP or UDP pseudo-header checksum. This bit should be set if IP
options need to be consulted in forming the pseudo-header checksum, as eTSEC does not
examine IP options or extension headers for TCP/IP offload on transmit.
0 Calculate TCP or UDP pseudo-header checksum as normal, assuming that the IP header
has no options.
1 Do not calculate a TCP or UDP pseudo-header checksum, but instead use the value in
field PHCS when determining the overall TCP or UDP checksum.
Reserved
Indication to the transmitter that this is a PTP packet. Enabling PTP disables per packet
VLAN tag insertion. Instead, VLAN tag will be read from the DFVLAN when the PTP field is
true.
0 Do not attempt to capture transmission event time
1 Valid PTP_ID field. When this packet is transmitted, capture the time of transmission.
Must be clear if TMR_CTRL[TE] is clear.
Layer 4 header offset from start of layer 3 header. The layer 4 header starts L4OS octets
after the layer 3 header if it is present. The maximum layer 3 header length supported is thus
255 bytes, which may prevent TCP/IP offload on particularly large IPv6 headers.
Layer 3 header offset from start of frame not including the 8 bytes for this FCB. The layer 3
header starts L3OS octets from the start of the frame including any custom preamble header
that may be present. The maximum layer 2 header length supported is thus 255 bytes.
Pseudo-header checksum (16-bit one's complement sum with carry wraparound, but without
result inversion) for TCP or UDP packets, calculated by software. Valid only if NPH = 1.
VLAN control word for insertion in the transmitted VLAN tag. Valid only if VLN = 1.Tx PTP
packet identification number. This number will be copied into the Tx PTP packet time stamp
identification field. PTP field takes precedence over VLN field.
Description
Figure 15-147). Data BDs
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