Axis mapping is inverted for those systems:

• FBA
• NeoGeo

There's something wrong with the button mapping. I suppose this file should map SNES buttons to X360 buttons. In that case, this line should be :

"a": "b", "b": "a", "x": "y", "y": "x",

With this modification, I get proper button mapping.

I want the stick to be able to manage both the hat and analogic and it works when the compat section contains:

[compat]
axis_dpad1_x = 0
axis_dpad1_y = 1

beside the main section

[dreamcast]
axis_y = 1
axis_x = 0

but reicastControllers isgnore the axis_dpad an removes them (keeps only triggers)
is it possible to have them added to the compat section ?

make a moonlight generator to import ES config since 3.3.0b17 as es_input.cfg now writes the expected button/axis/hat code values expected by moonlight mapping files

Expect some changes in recalbox-buildroot to move configuration files to /recalbox/conf/moonlight

Have 2 joysticks.
Configure :
JOY1 => P1
JOY2 => P2

Unplug JOY1.

P1 is marked as DEFAULT
P2 is marked as JOY2.

This is ok.
Start a game.

It calls :
emulatorlauncher.pyc -p2index 0 -p2guid 03000000a30600000cff000010010000 -p2name "Saitek PLC Cyborg Force Rumble Pad" -p2devicepath /dev/input/event0 -system snes -rom /recalbox/share/roms/snes/DonkeyKongClassic\ (Shiru).smc -emulator default -core default

An it seems that in case there is no p1, no other player switch to p1.
Thus, you cannot quit or play.
More generally, it there is a whole, for example :
p1 p4 => replace p4 by p2...

See
https://github.com/recalbox/recalbox-configgen/blob/master/configgen/controllersConfig.py#L65

In 4.1 unstable, PPSSPP doesn't recognize my Buffalo Classic SNES gamepad at all.
The interesting thing is that the gamepad identifies as USB,2-axis 8-button gamepad in its deviceName.
I strongly guess the comma in the name breaks the SDL gamecontrollerDB.txt file, since it expects comma as the delimiter and no string quotes.
I have no toolchain setup at the moment so I can't test it myself, but I hope this helps.

The gamecontrollerdb.txt entry looks like this:

03000000830500006020000010010000,USB,2-axis 8-button gamepad  ,platform:Linux,b:b0,a:b1,x:b3,leftshoulder:b4,dpup:a1,dpdown:a1,start:b7,dpright:a0,rightshoulder:b5,guide:b6,y:b2,back:b6,dpleft:a0,

Create a directory where configuration files can be added in order to let user override the configuration for a platforme, or even a game.

The directory structure should be like :

/recalbox/share/system/customconfigs/  

in this directory, create the files with names corresponding to the system you want to configure :

/recalbox/share/system/customconfigs/snes.cfg

or even the game

/recalbox/share/system/customconfigs/snes/Street Fighter 2 Turbo.cfg

If one of those files exist, the auto generated config will be ignored, and your configuration will be loaded.

These lines in libretroconfig.py force any bilinear filtering off as soon as shaders are enabled in ES or recalbox.conf. This causes the important statement linear_filter0="true" in any glslp file to have no effect whatsoever:
if defined('shaders', recalboxConfig):
retroarchConfig['video_shader'] = recalboxConfig['shaders']
retroarchConfig['video_shader_enable'] = 'true'
retroarchConfig['video_smooth'] = 'false'

This breaks shaders_glsl/retro/sharp-bilinear.glslp and probably many other presets that rely on linear filtering to actually work as intended. Shaders are NOT just masks. For example sharp-bilinear with a pre-scale of 2 or 3 is the ONLY filter that gives sharp pixels with minimum blurring without any pixelwobble during scrolling at non-integer scalings. It would be great to have sharp-bilinear, with a pre-scale of 2, as one of the presets that the user can choose. But for it to work, the video_smooth should NOT be turned off automatically.

One quick fix would be to add a allow_smoothing_with_shaders option in recalbox.conf to allow advanced users who want to bypass this behaviour to do so.

EDIT: Nevermind it works identical to smoothing if the shader defined linear_filterx = "true" for anything but the LAST shader pass.

It would be nice to match the controller mapping from Glupen64 to the one used by Mupen64plus.

As we are forcing input devices with the generator, we just map joysticks, no keyboard nor mouse