by support »
Hello,
In principle, I can think of three directions:
(1) Speed up the configuration of the FPGA from the SPI flash by setting the configuration clock's frequency, if you haven't done that already. I'm however not sure if that will be fast enough.
(2) Apply the TANDEM technique to partially configure the FPGA quickly at powerup so it presents an PCIe interface, and then do the complete configuration at a longer time.
(3) Hold the PC's reset button wire asserted with a pullup/pulldown resistor, and deassert this reset signal one of the FPGA's pins once it's configured (probably through a FET transistor, depending on the voltage on the reset wire). Since the FPGA's pins are all high-Z until it's configured, all you need to do is to assign a constant value to this line in the logic design.
I believe option (3) will be simplest to pull off. The only annoying thing is that if you configure the FPGA through the JTAG cable while the PC is up, you'll have an abrupt reset. It's a refined version of your suggestion to power up the motherboard.
Regards,
Eli