About the qmk config: how does the layout macro work?

[x4Cx58x54]

Hi! I found this project very interesting and I am trying to understand your qmk configuration code. You see, the keymap array has size num_layerxMATRIX_ROWSxMATRIX_COLS, that is, n x 8 x 10 in this project. However, the LAYOUT macro seems to disagree, as it has a different size. I doubt this definition will map the second row on the left side to the first row of the right side. Would you be so kind to explain why it works?

[pierrechevalier83]

As far as qmk is concerned, the keyboard has 8 rows of 5 columns: 4 per keyboard half.

The layout macro describes how to map one list of keys which are layed out like the physical keys on the keyboard (could be seen as 3 rows of 10 + 1 row of 4) into the firmware's view of the keyboard.

Does that make more sense?

[x4Cx58x54]

And that is to say, although 8x10 space is allocated for keymap array, half of it is used and the other half remains empty. I think I got it. Thanks!

[pierrechevalier83]

Oh. I see. The surprising lines of code are this one: https://github.com/qmk/qmk_firmware/blob/8f660ca1e652b3b53580442d321642165adbc7d0/keyboards/ferris/0_2/config.h#L29 which defines MATRIX_COLS at 10 and this one: https://github.com/qmk/qmk_firmware/blob/8f660ca1e652b3b53580442d321642165adbc7d0/keyboards/ferris/0_2/config.h#L54 which allocates A1 to the 5 rightmost pins.

This does feel like an oversight now we've discussed it. As well as the one where A1 is alloca