iPXE normally operates in polling mode with interrupts disabled. Drivers may choose to support the use of interrupts, but this is not required.
Interrupt-based operation can be tested by using iPXE to boot into the undionly.kpxe build of iPXE.
Create a 512MB file containing pseudo-random data, using e.g.:
dd if=/dev/urandom of=512mb bs=1M count=512
Download undionly.kpxe.
Copy both your pseudo-random data file and undionly.kpxe to a web server on your local network.
undionly.kpxe.net0).dhcp net0.undionly.kpxe using chain.Ctrl-B to enter the iPXE shell provided by undionly.kpxe.ifstat to verify that undionly.kpxe has detected a single interface net0 with the correct MAC address and using the undionly driver.dhcp net0.imgfetch.imgstat to verify that the downloaded file has the correct size.