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Adapter Host Registers
A-16
Table A–5. Host
_
CMD Register Bits (Continued)
Bit FunctionName
14 Ld_Tmr Load interrupt timer
4
: Writing a 1 to this bit causes the interrupt holdoff timer to be loaded
from the Ack Count field. Ack Count indicates the time-out period in 4-µs units (based
on a 33-MHz PCI clock). The interrupt holdoff timer is used to pace interrupts to the host.
Host interrupts are disabled (PCI interrupt request line deasserted) for the time-out peri-
od of the timer after an Ack bit write. The timer is restarted on every Ack bit write.
13 Ld_Thr Load Tx interrupt threshold
5
: Writing a 1 to this bit causes selected transmit channel
interrupt threshold to be loaded from the Ack count field. For this operation to be valid
(take effect), the following parameters must be set: Nes = 0, EOC = 0, R/T = 0, and
Ch_Sel must indicate the selected transmit channel.
Set Ack count to
indicate the Tx interrupt threshold in number of EOF interrupts. This
threshold determines the number of Tx EOF interrupts that must occur before a Tx EOF
interrupt is posted. If the threshold is set to 0, no Tx EOF interrupts are posted.
12 Req_Int Request host interrupt: Writing a 1 to this bit creates a dummy ThunderLAN interrupt.
Writing a 0 to this bit has no effect. This bit is always read as 0.
11 Ints_off Turn PCI interrupts off: Writing a 1 to this bit disables ThunderLAN interrupts to the host
(PINTA# will never be asserted). Writing a 0 to this bit has no effect. This bit is always
read as 0.
10 Ints_on Turn PCI interrupts on: Writing a 1 to this bit reenables ThunderLAN interrupts after an
Ints_off command bit write. Writing a 0 to this bit has no effect. This bit is always read
as 0.
9–8 0 These bits are reserved and are always written as 0s.
7–0 Ack count EOF acknowledge count: This field is primarily used to acknowledge Rx or Tx EOF in-
terrupts in conjunction with the Ack command bit. It is set with the number of frames
(lists) serviced by the host interrupt routine in response to the interrupt. The adapter
then uses this parameter to determine if the host has serviced all outstanding frame in-
terrupts, and therefore, whether to generate a further EOF interrupt.
This field is also used to pass interrupt threshold and timer values in conjunction with
the Ld_Tmr and Ld_Thr command bits.
4) The interrupt timer value may be reloaded at any time. If the timer had already timed out, it remains that way.
If it has not yet timed out, it does so when the new timer value is reached or surpassed.
5) The threshold value may be reloaded at any time. Increasing the threshold value causes a current interrupt
to be deasserted if the old threshold value has been reached and the new threshold hasn’t.