PERST pin differences LTE Base HAT vs Base Shield

Dear sixfab,

we are experiencing a problem with an LTE modem connected to the BaseHat, specifically an MPCI-L210 u-blox LTE modem, which keeps restarting over and over.

Since software resets we attempted so far have proven to be insufficient, we are looking at the possibility of a hardware reset, which with the MPCI-L series would mean pulling the PERST# pin to GND for 2.1s. For details, see MPCI-L2 DataSheet (UBX-13004749) at chapter 4.2.7, page 19, and TOBY-L2-MPCI-L2 SysIntegrManual (UBX-13004618) at chapter 1.6.3, page 34.

Unfortunately we do not have access to the PERST# PCI pin, even though the PERST pin is connected in the Base HAT schematics, it is not brought to a test point or connected elsewhere. This is when we noticed a design change on the Base HAT with respect to the older Base Shield v2. GPIO26 used to be connected to the PERST# pin in the Base Shield schematics, while on the Base HAT it is connected to the PWR_DISABLE_P.

What was the reason for moving away from the PERST# pin, and implementing a PWR_DISABLE_P in the Base HAT?

We also developed a custom board with the PERST# pin connected normally to the other PCI modules and an FPGA. When the MPCI module reboots, it causes a reboot of the entire system. For this reason we were curious about the design change in the Base HAT, with respect to the Base Shield, as we might face a similar issue.