Delaying a motherboard's BIOS/UEFI boot is a simple trick that solves issues related to the PCIe Specification's 100ms time limit. This can be done by toggling a computer's POWER button, then pressing and holding the RESET button for a second before releasing it. Or, connect a capacitor across the reset pins of an ATX motherboard's Front Panel Header.
This board is a simple 9-Pin Front Panel Header in-line replacement for ATX motherboards that allows choosing capacitor(s) to connect accross the RESET pins to delay boot.
To use the RESET button on the board, hold it long enough to overcome the capacitor discharge delay which can be a couple of seconds.
Close-up:
| Designator(s) | Part Number | Quantity | Value | Footprint | Availability |
|---|---|---|---|---|---|
| C1 | 860010674014 | 1 | 100uF | C_Radial_D8.0mm_H11.5mm_P3.50mm | DigiKey |
| C2 | 860010374011 | 1 | 330uF | C_Radial_D8.0mm_H11.5mm_P3.50mm | DigiKey |
| C3 | 860020274013 | 1 | 680uF | C_Radial_D8.0mm_H11.5mm_P3.50mm | DigiKey |
| C4 | 860010274015 | 1 | 1000uF | C_Radial_D8.0mm_H11.5mm_P3.50mm | DigiKey |
| SW1, SW2 | TS02-66-60-BK-100-LCR-D | 2 | N/A | SW_PUSH_6mm | DigiKey |
| J1 | PREC005DBAN-M71RC | 1 | N/A | PinSocket_2x05_P2.54mm_Horizontal | DigiKey |
| J2 | PPTC052LJBN-RC | 1 | N/A | PinHeader_2x05_P2.54mm_Horizontal | DigiKey |
| J3 | 9-146257-0-04 | 1 | N/A | PinHeader_2x04_P2.54mm_Vertical | DigiKey |
| D1 | C503B-RAN-CZ0C0AA2 | 1 | RED | LED_D5.0mm | DigiKey |
| D2 | LTL-4234 | 1 | GREEN | LED_D5.0mm | DigiKey |
| R1, R2, R3 | CF14JT220R | 1 | 220-Ohm | R_Axial_DIN0207_L6.3mm_D2.5mm | DigiKey |
| Jumpers | QPC02SXGN-RC | 4 | N/A | N/A | DigiKey |
The capacitor across RESET works thanks to an RC Delay on the reset signal buffer. The OpenCompute project has a public schematic and the RESET Button is on Pg#151 in Project_Olympus_Intel_XSP_Schematics_20171016.pdf found in Project_Olympus_Intel_XSP_Collateral.zip.
A standard Schmitt-Trigger inverter such as the SN74LVC1G14 has a positive-going threshold voltage of about 1.5V with a 3.3V supply. I have measured 1k-Ohm between the RESET+ pin and the 3.3V ATX Power supply rail. A 330uF capacitor therefore delays boot by about 200ms. RC Calculator:
I found out about this technique here:
