Fix BCORNE firmware build for vial-qmk on modern Python.

Include m57.c for RGB matrix linking, add Python 3.14 math patch and platform fallback, and keep brightness step in info.json only.

corne/firmware/config.h

@@ -89,7 +89,6 @@
 #    define WS2812_DMA_CHANNEL 5  // DMA Channel for TIMx_UP, see the respective reference manual for the appropriate values for your MCU.
 //#    define WS2812_DMAMUX_ID STM32_DMAMUX1_TIM2_UP // DMAMUX configuration for TIMx_UP -- only required if your MCU has a DMAMUX peripheral, see the respective reference manual for the appropriate values for your MCU.
 #define RGB_MATRIX_SLEEP
-#define RGB_MATRIX_VAL_STEP 1
 
 #define WEAR_LEVELING_LOGICAL_SIZE 2048
 #define WEAR_LEVELING_BACKING_SIZE (WEAR_LEVELING_LOGICAL_SIZE * 2)

corne/firmware/patches/vial-qmk-math-py.patch

@@ -0,0 +1,15 @@
+--- a/lib/python/qmk/math.py
++++ b/lib/python/qmk/math.py
+@@ -23,8 +23,10 @@ def compute(expr):
+ 
+ 
+ def _eval(node):
+-    if isinstance(node, ast.Num):  # <number>
+-        return node.n
++    if isinstance(node, ast.Constant) and isinstance(node.value, (int, float, complex)):
++        return node.value
++    elif isinstance(node, ast.Num):  # <number> (Python <3.14)
++        return node.n
+     elif isinstance(node, ast.BinOp):  # <left> <operator> <right>
+         return operators[type(node.op)](_eval(node.left), _eval(node.right))
+     elif isinstance(node, ast.UnaryOp):  # <operator> <operand> e.g., -1

corne/firmware/post_rules.mk

@@ -0,0 +1,3 @@
+# Fallback when qmk info parsing fails (e.g. Python 3.14+ ast.Num removal).
+MCU ?= STM32F401
+PLATFORM_KEY ?= chibios

corne/firmware/readme.md

@@ -5,7 +5,8 @@ Keyboard target: `sh01/m36:via`
 ## Prerequisites
 
 1. Install [QMK CLI 1.2.0](https://docs.qmk.fm/#/cli) (or QMK MSYS on Windows).
-2. Clone vial-qmk at the IFKB-pinned commit:
+2. Use **Python 3.11 or 3.12** for the build. Python 3.14 breaks the pinned vial-qmk commit unless patched (see Troubleshooting).
+3. Clone vial-qmk at the IFKB-pinned commit:
 
 ```bash
 git clone https://github.com/vial-kb/vial-qmk.git
@@ -25,6 +26,13 @@ cp -r /path/to/kb-layouts/corne/firmware/* keyboards/sh01/m36/
 
 The make target comes from that path: `keyboards/sh01/m36` → `sh01/m36:via`.
 
+If you are on Python 3.14+, apply the QMK math patch from inside your vial-qmk checkout:
+
+```bash
+cd /path/to/vial-qmk
+patch -p1 < /path/to/kb-layouts/corne/firmware/patches/vial-qmk-math-py.patch
+```
+
 ## Build
 
 ```bash
@@ -47,11 +55,25 @@ After flashing, load `../corne.vil` in Vial to restore your keymap.
 
 ## RGB brightness dial
 
-Brightness step size is controlled in `config.h`:
+Brightness step size is set in `info.json` under `rgb_matrix.val_steps` (currently `1`).
 
-```c
-#define RGB_MATRIX_VAL_STEP 1
-```
+With `max_brightness: 50`, step `1` gives 51 brightness levels. Increase to `2` or `4` if the dial feels too slow.
 
-With `max_brightness: 50` in `info.json`, step `1` gives 51 brightness levels.
-Increase to `2` or `4` if the dial feels too slow.
+Do not also define `RGB_MATRIX_VAL_STEP` in `config.h` — QMK warns when both are set.
+
+## Troubleshooting
+
+### `AttributeError: module 'ast' has no attribute 'Num'`
+
+The pinned vial-qmk commit uses `ast.Num`, which was removed in Python 3.14. Fix options:
+
+1. **Recommended:** build with Python 3.11 or 3.12 (`python3.12 -m venv .venv && source .venv/bin/activate && pip install qmk`).
+2. **Alternative:** apply `patches/vial-qmk-math-py.patch` inside your vial-qmk checkout (see Install step above).
+
+### `Platform not defined`
+
+Usually a follow-on error from the `ast.Num` failure — QMK never parses `processor: STM32F401` from `info.json`. Fixing the Python issue should resolve this. `post_rules.mk` also provides a fallback (`PLATFORM_KEY = chibios`, `MCU = STM32F401`).
+
+### `RGB_MATRIX_VAL_STEP in config.h is overwriting rgb_matrix.val_steps in info.json`
+
+Keep the step size in **one place only** — use `val_steps` in `info.json`, not `#define RGB_MATRIX_VAL_STEP` in `config.h`.

corne/firmware/rules.mk

@@ -24,5 +24,6 @@ SRC += rtt_viewer/SEGGER_RTT.c
 
 CUSTOM_MATRIX = lite
 SRC += matrix.c
+SRC += m57.c
 # SRC += split_util_qf.c
 ALLOW_WARNINGS = yes