Introduce minimal chip support for the STMicro STM32N6 family
(Cortex-M55, ARMv8.1-M with TrustZone and FPU), sufficient to bring
up an NSH console over USART1.
Scope (deliberately minimal first drop):
- Chip selector ARCH_CHIP_STM32N6 wired into arch/arm/Kconfig and
chip-name mapping ("stm32n6").
- Sub-Kconfig under arch/arm/src/stm32n6 with the STM32N657X0 chip
selector and a single user-selectable USART (USART1).
- Boot path: stm32_start with a naked dispatcher that clears the
boot-ROM MSPLIM/PSPLIM stack limits before any compiler-emitted
prologue, then runs vector relocation and SRAM-only heap init.
The chip runs entirely in the Secure state; SAU is left in its
reset configuration.
- PLL1-based clock tree fed from HSI64 targeting 200 MHz CPU, with
USART1 kernel-clock routed to HSI for a predictable BRR that is
independent of any later clock change.
- Low-level USART driver with full serial framework support.
stm32_serial.c is adapted from arch/arm/src/stm32h5/stm32_serial.c
(sibling ARMv8-M Mainline port with the same USART IP), stripped
of DMA-RX, LPUART, the per-USART2..5 plumbing, RS-485 driver-enable,
TIOCSINVERT/SWAP and HALFDUPLEX paths.
- SysTick system timer.
- GPIO, PWR and RCC helpers.
TrustZone, MPU, I/D-cache and Helium (MVE) are left disabled to
minimise bring-up surface; these will be added in follow-up patches
alongside the drivers that need them.
Signed-off-by: ImBonkers <samuelnlinden@pm.me>
CI Build Job `arm-05` (runtime 2 hours) has become the Performance Bottleneck for CI Workflow. That's because `arm-05` builds too many targets for nRF, RP2040, SAM 3, SAM A and SAM D. This PR splits `arm-05` into multiple smaller jobs, to reduce the CI Build Duration.
Before the PR: `arm-05` is overloaded, build requires 2 hours
- `arm-05` (2 hours): nRF, RP2040, SAM 3, SAM A, SAM D
- `arm-06` (56 mins): STM32 [a-m]*
After the PR: `arm-05` is offloaded (to `arm-06` and `arm-07`), completes within 1 hour
- `arm-05` (47 mins): nRF
- `arm-06` (1 hour): Reserve for RP2040 exclusively
- `arm-07` (1 hour 15 mins): SAM 3, SAM A, SAM D, STM32 [a-m]*
Build Jobs are sorted by Target Name. So we cascade the changes and rename the Build Jobs: `arm-07` becomes `arm-08`, `arm-08` becomes `arm-09` etc. Then `arm-13` becomes a new job `arm-14`. (Which we added to `build.yml`)
Performance of `arm-05` is discussed in https://github.com/apache/nuttx/issues/13775 and https://github.com/apache/nuttx/issues/12773
ImBonkers
Lup Yuen Lee