I am trying to build a board to bridge the MXM slot in my laptop with a PCIe riser. Have just started working out which pins from the MXM slot should connect to which pin on a PCIe slot. I have put my initial planning work on github - https://github.com/gautamz/mxm3-pcie-rise-connector.
I need help with the following MXM pins,
- PWR_GOOD & PEX_RST# - PWR_GOOD indicates to the board that the internal power state of the endpoint is fine. On PCIe this is indicated by PERST#. So I am connecting these two. But then what do I connect the PEX_RST# pin on the MXM slot to? Can I just leave this unconnected? Setting PWR_GOOD is important to ensure I get PCIe v3 speeds, or else the system will default to PCIe v1.
- PEX_STD_SW# - This determines the swing for the MXM GPU. However I saw nothing for this in PCIe specifications. There the swing appears to be managed by the REFCLK signals. In the MXM specs if I connect this to ground I am indicating standard (desktop) swing. Should I connect this to ground, or leave it unconnected?
- 3V3 - Do I need to connect the PCIe 3.3V pins to the 3V3 pins on the MXM slot?
- I am planning to only connect to the following MXM pins - WAKE#, PWR_GOOD, SMB_DAT, SMB_CLK, PEXRXn & PEXTXn (n = 0 to 15), PEX_REFCLK, PEX_CLK_REQ#, PEX_RST#(?), PEX_STD_SW#(?). This should be enough for the PCIe card since I will power it with an external PSU. Any other MXM connections are mandatory?
In the github repo I have a spread sheet where I am working out the needed pin connections before I begin working on the PCB layout. If you have any other advice for this, it would be appreciated. I will also put up the PCB layouts on the github repo.