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length of 64 Bytes. When CRC is not automatically generated (as defined in word 1 of the transmit buffer
descriptor), the frame is assumed to be at least 64 Bytes long and pad is not generated.
An entry in the transmit buffer descriptor list is described in this table:
Table 24-3. Transmit Buffer Descriptor Entry
Bit Function
Word 0
31:0 Byte address of buffer
Word 1
31 Used—must be zero for the GMAC to read data to the transmit buffer. The GMAC sets this to
one for the first buffer of a frame once it has been successfully transmitted. Software must clear
this bit before the buffer can be used again.
30 Wrap—marks last descriptor in transmit buffer descriptor list. This can be set for any buffer within
the frame.
29 Retry limit exceeded, transmit error detected
28 Reserved.
27 Transmit frame corruption due to AHB error—set if an error occurs while midway through reading
transmit frame from the AHB, including HRESP errors and buffers exhausted mid frame (if the
buffers run out during transmission of a frame then transmission stops, FCS shall be bad and
GTXER asserted).
Also set if single frame is too large for configured packet buffer memory size.
26 Late collision, transmit error detected.
25:23 Reserved
22:20 Transmit IP/TCP/UDP checksum generation offload errors:
000: No Error.
001: The Packet was identified as a VLAN type, but the header was not fully complete, or had an
error in it.
010: The Packet was identified as a SNAP type, but the header was not fully complete, or had an
error in it.
011: The Packet was not of an IP type, or the IP packet was invalidly short, or the IP was not of
type IPv4/IPv6.
100: The Packet was not identified as VLAN, SNAP or IP.
101: Non supported packet fragmentation occurred. For IPv4 packets, the IP checksum was
generated and inserted.
110: Packet type detected was not TCP or UDP. TCP/UDP checksum was therefore not
generated. For IPv4 packets, the IP checksum was generated and inserted.
111: A premature end of packet was detected and the TCP/UDP checksum could not be
generated.
19:17 Reserved
SAM D5x/E5x Family Data Sheet
GMAC - Ethernet MAC
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 486