From 8cc9fc21a973bd5b9cdf8be47b14b1373eb9ac02 Mon Sep 17 00:00:00 2001 From: Tobias Schramm Date: Fri, 23 Oct 2020 23:49:36 +0200 Subject: [PATCH] Explain jumper settings --- README.md | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/README.md b/README.md index 18e56de..227c312 100644 --- a/README.md +++ b/README.md @@ -24,3 +24,41 @@ This board has been designed to bring the front FlexibleLOM mounting hole as close as possible to the PCIe bracket retention screw on a full size PCIe slot. You can use a small angled metal piece or a even a 3d printed one to mount the card into place. + +# Jumpers + +This adapter cards has several jumpers. You should not need to touch them, however +the following sections will explain their purpose. + +## PERST + +This jumper selects where the PCIe reset signal is routed. By default it is routed +to A1 on the FlexibleLOM slot. I believe this to be the PCIe reset signal. However, +there is also another pin on the connector, A14 which behaves similarly to A1. +Testing has shown that the cards does not always enumerate properly when using A14 +as PCIe reset. +The two resistor footprints next to this jumper can be populated in case you are +having issues with floating resets on the cards resulting in spurious resets. I +have not encountered any such issues. + +## Vdet + +The Vdet jumper bridges +12V to pin B1 on the FlexibleLOM slot. I assume B1 to be +some sort of voltage detection pin since it is routed very differently from all +other +12V power signals on the card. + +## 3v3 aux + +The 3v3 aux jumper connects what I think is the auxiliary 3v3 volt voltage supply +on the FlexibleLOM slot to the auxiliary 3v3 supply of the PCIe connector. Most +cards I've seen do not use this voltage rail. However I assume there might be some +that utilize it for WOL capability. + +## lanes + +This jumper controls which PRSNT2 pin is bridged to PRSNT1. It defaults to PRSNT2 +for 8x cards since that is the maximum number of lanes on a FlexibleLOM slot. You +can try setting this jumper to 4x if you are having issues with card detection. +However, a lot of modern devices tend to ignore the PRSNT2 line and rely solely on +detecting the lane transmitters/receivers. Thus this setting will be irrelevant for +most devices.