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Receive and Transmit Description
Software Developer’s Manual 39
Notes:
1. VLE, IFCS, and IC are qualified by EOP. That is, hardware interprets these bits ONLY when
EOP is set.
2. Hardware only sets the DD bit for descriptors with RS set.
3. Descriptors with the null address (0b) or zero length transfer no data. If they have the RS bit
set then the DD field in the status word is written when hardware processes them.
4. Although the transmit interrupt may be delayed, the descriptor write-back requested by setting
the RS bit is performed without delay unless descriptor write-back bursting is enabled.
3.3.3.2 Transmit Descriptor Status Field Format
The STATUS field stores the applicable transmit descriptor status and has the fields shown in Table
3-11.
The transmit descriptor status field is only present in cases where RS (or RPS for the 82544GC/EI
only) is set in the command field.
Table 3-11. Transmit Status Layout
IC (bit 2)
Insert Checksum
When set, the Ethernet controller needs to insert a checksum at the offset indicated
by the CSO field. The checksum calculations are performed for the entire packet
starting at the byte indicated by the CCS field. IC is ignored if CSO and CCS are out
of the packet range. This occurs when (CSS ≥ length) OR (CSO ≥ length - 1). IC is
valid only when EOP is set.
IFCS (bit 1)
Insert FCS
Controls the insertion of the FCS/CRC field in normal Ethernet packets. IFCS is
valid only when EOP is set.
EOP (bit 0)
End Of Packet
When set, indicates the last descriptor making up the packet. One or many
descriptors can be used to form a packet.
TDESC.CMD Description
321 0
RSV
TU
a
a. 82544GC/EI only.
LC EC DD