Using Keyrah V3
3.7 Using a custom Keymap
The builtin default keyboard mapping can be replaced by a custom mapping. This mapping needs to
be created in an external tool in .uf2 format and then flashed: Either press and hold the button, then
connect Keyrah to USB, or press and hold the button for about 5 seconds. Your computer will detect
a new mass storage device – open it and then drag&drop the .uf2 file on it. The file will get flashed
and the device will unmount itself. The new mapping is now active. This mapping will then be used
for ALL keyboards, so in order to use Keyrah with a different type of keyboard (or the default
mapping) again, you will have to remove the custom mapping again (just flash an empty file that
contains no signature tag).
Details on the .uf2 format can be found on the Microsoft github repository and are out of scope of
this document: https://github.com/microsoft/uf2
3.7.1 Flash organisation
The last 4KiB of the Flash Memory are reserved for a user defined Keyboard configuration. Those
4KiB are organised in 4 blocks, each of which contains the keyboard mapping for one of the 4
configurations that can be selected by using the power switch and the EN/DE jumper.
Jumper Switch Flash Offset Block
US normal
101FF000
Block 0
US emu
101FF400
Block 1
DE normal
101FF800
Block 2
DE emu
101FFC00
Block 3
Now, each block contains 3 keyboard mapping layers, plus a tag at the end.
Offset
+ 0x000 Normal Keymap (Layer 1)
+ 0x100 (Layer 2) extra Keys with Shift (CBM Keyboards only)
+ 0x200 (Layer 3) extra Keys with “Fn”
+ 0x3F0 “KeyrahV3 Keymap”, 0
The tag is checked per block, so only blocks with a valid tag will enable the custom mapping for
that configuration.
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