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314 Software Developer’s Manual
Register Descriptions
13.4.40 Transmit Descriptor Tail
TDT (03818h; R/W)
This register contains the tail pointer for the transmit descriptor ring. It holds a value that is an
offset from the base, and indicates the location beyond the last descriptor hardware can process.
This is the location where software writes the first new descriptor. It points to a 16-byte datum.
Software writes the tail pointer to add more descriptors to the transmit ready queue. Hardware
attempts to transmit all packets referenced by descriptors between head and tail.
Table 13-83. TDT Register Bit Description
13.4.41 Transmit Interrupt Delay Value
TIDV (03820h; R/W)
This register contains the transmit interrupt delay value. It determines the amount of time that
elapses between writing back a descriptor that has Report Status (RS) [or Report Packet Sent (RPS)
for the 82544GC/EI] and Interrupt Delay Enable (IDE) set in the transmit descriptor and when the
IMS.TXDW (Transmit Descriptor Written Back) interrupt bit is set. Counts are in units of 1.024
µs. A value of 0b is not allowed. The TIDV value is used to force timely write–back of descriptors
as well. The first packet after timer initialization starts the timer. Timer expiration flushes any
accumulated descriptors and sets an interrupt event (TXDW).
Field Bit(s)
Initial
Value
Description
TDH 15:0 0b Transmit Descriptor Head
Reserved 31:16 0b
Reserved
Reads as 0b. Should be written with 0b for future compatibility.
31 16 15 0
Reserved TDT
Field Bit(s)
Initial
Value
Description
TDT 15:0 0b Transmit Descriptor Tail
Reserved 31:16 0b
Reserved
Reads as 0b. Should be written to 0b for future compatibility.