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Diffstat (limited to 'Documentation/getting_started/gpio.md')
| -rw-r--r-- | Documentation/getting_started/gpio.md | 23 |
1 files changed, 16 insertions, 7 deletions
diff --git a/Documentation/getting_started/gpio.md b/Documentation/getting_started/gpio.md index 19e74eec11..5d5623a5d9 100644 --- a/Documentation/getting_started/gpio.md +++ b/Documentation/getting_started/gpio.md @@ -130,24 +130,24 @@ pads defaulting to GPIO mode have this bit set. However, in the mainboard's GPIO configuration the macro `PAD_NC(pad, NONE)` can be used to explicitly configure a pad as unconnected. -In case there are no schematics available for a board and the vendor sets a pad -to something like `GPIORXDIS=1`, `GPIOTXDIS=1` with an internal pull resistor, -an unconnected or otherwise unused pad can be assumed. In this case it is -recommended to keep the pull resistor, because the external circuit might rely -on it. +In case there are no schematics available for a board and the vendor set a +pad to something like `GPIORXDIS=1`, `GPIOTXDIS=1` with an internal pull +resistor, an unconnected or otherwise unused pad can be assumed. In this case it +is recommended to keep the pull resistor, because the external circuit might +rely on it. Unconnected pads defaulting to a native function (input and output) usually don't need to be configured as GPIO with the `GPIORXDIS` bit set. For clarity and documentation purpose the macro may be used as well for them. Some pads configured as native input function explicitly require external -pull-ups when unused, according to the PDGs: +pull-ups when being unused, according to the PDGs: - eDP_HPD - SMBCLK/SMBDATA - SML0CLK/SML0DATA/SML0ALERT - SATAGP* -If the board was designed correctly, nothing needs to be done for them +When the board was designed correctly, nothing needs to be done for them explicitly, while using `PAD_NC(pad, NONE)` can act as documentation. If such a pad is missing the external pull resistor due to bad board design, the pad should be configured with `PAD_NC(pad, NONE)` anyway to disconnect it @@ -162,6 +162,15 @@ The first is configuring a pin as an output, when it was designed to be an input. There is a real risk in this case of short-circuiting a component which could cause catastrophic failures, up to and including your mainboard! +## Soft Straps + +Soft straps, that can be configured by the vendor in the Intel Flash Image Tool +(FIT), can influence some pads' default mode. It is possible to select either a +native function or GPIO mode for some pads on non-server SoCs, while on server +SoCs most pads can be controlled. Thus, it is generally recommended to always +configure all pads and don't just rely on the defaults mentioned in the +datasheet(s) which might not reflect what the vendor configured. + ## Pad-related known issues and workarounds ### LPC_CLKRUNB blocks S0ix states when board uses eSPI |