fix(boards): correct the F412 chip selection and app flash size on ARK cannodes

[dakejahl]

Summary

Name the ARK cannodes after the parts they actually use — STM32F412VG on the 100-pin boards (including DIST), STM32F412CG on CANnode — give every 1MB board 960K of app flash, and open the F412 SRAM region to 256K.

Problem

Flow MR, DIST, Teseo, X20, F9P, Septentrio/MOSAIC/G5 and MAG are STM32F412VGH6 and CANnode is STM32F412CGU6, but Kconfig only listed the 48-pin 512KB CE, so all of them selected it. Note that the chip selection is not what sets the flash size — STM32_FLASH_SIZE comes from CONFIG_STM32_FLASH_CONFIG_G, which these boards already set. CE was wrong as documentation, and it capped STM32_NGPIO at 34.

Separately, the app linker scripts subtracted the 32K param window twice. App flash starts at 0x08010000 after the 64K bootloader+params reservation, so the region is 960K, not 928K; the canbootloader always computed 960K, so the two disagreed by a sector.

The linker scripts also still described the F42x 192K SRAM split, so .data/.bss could not use the upper 64K.

Solution

NuttX 12.12 already has VG/CG (PX4/NuttX#405) and ends the F412 heap at 0x20040000 (PX4/NuttX#407). Select VG/CG per board, set app flash LENGTH to 960K, set sram LENGTH to 256K on all ARK F412 cannodes (VG/CG and the remaining CE boards), and map VG/CG to a DEBUG_DEVICE. The linker comments also described an SRAM split the F412 does not have — it is one contiguous 256KB block at 0x20000000.

[github-actions]

🔎 FLASH Analysis

px4_fmu-v5x [Total VM Diff: 0 byte (0 %)]

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +55  [ = ]       0    .debug_abbrev
  -0.0%      -2  [ = ]       0    .debug_info
  -0.0%      -5  [ = ]       0    .debug_line
     +50%      +2  [ = ]       0    [Unmapped]
    -0.0%      -7  [ = ]       0    [section .debug_line]
  +0.0%     +48  [ = ]       0    TOTAL

px4_fmu-v6x [Total VM Diff: 0 byte (0 %)]

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +55  [ = ]       0    .debug_abbrev
  -0.0%      -2  [ = ]       0    .debug_info
  -0.0%      -5  [ = ]       0    .debug_line
     +50%      +2  [ = ]       0    [Unmapped]
    -0.0%      -7  [ = ]       0    [section .debug_line]
  +0.0%     +48  [ = ]       0    TOTAL

Updated: 2026-09-03T23:58:39

[dakejahl]

Holding off on this until the nuttx bump PR is merged