Verwendung
- Installationsbefehl kopieren und das Quellpaket vor der Installation in der eigenen Agentenumgebung prüfen.
- Benötigte Werkzeuge, Zugangsdaten und Hosts im Original prüfen.
- Eingabe und gewünschtes Ergebnis beschreiben und die Ausgabe mit den Quellen abgleichen.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill baremetal-startupVor dem Start
- Die Installation umfasst weder Modellabo noch API-Kontingent oder Dateizugriffsrechte.
- Sterne und Installationen zeigen Aktivität, keine unabhängige Qualitäts- oder Sicherheitsprüfung.
Originales Skill-Dokument
Aus dem Quell-Repository gerendert; Überschriften, Beispiele, Code, Tabellen, Links und Bilder bleiben erhalten.
Bare-Metal Startup
Purpose
Guide agents through bare-metal startup from reset to main(): reset and exception vectors, .data/.bss initialization, stack and heap setup, C runtime integration with linker scripts, and common Cortex-M and RISC-V bring-up bugs.
When to Use
- Firmware hangs before reaching
main() - Porting to a new MCU without vendor HAL
- Writing custom
startup.sorReset_Handler - Integrating with
skills/embedded/linker-scripts - Debugging uninitialized globals or stack overflows at boot
Workflow
1. Boot sequence mental model
Power-on / reset
├── CPU loads SP from vector[0]
├── CPU branches to Reset_Handler from vector[1]
├── Reset_Handler: init clocks (optional), copy .data, zero .bss
├── Configure stack pointer (if not already from vector)
├── Call SystemInit() / platform_init()
└── Call main() — must not return (loop or WFI)2. Cortex-M vector table
On Cortex-M, the vector table starts at address 0 or a relocatable base (VTOR):
| Index | Entry |
|---|---|
| 0 | Initial stack pointer (_estack) |
| 1 | Reset_Handler |
| 2 | NMI_Handler |
| 3 | HardFault_Handler |
| 4+ | IRQ handlers per NVIC |
asm
/* startup.s — minimal Cortex-M */
.syntax unified
.thumb
.section .isr_vector,"a",%progbits
.global g_pfnVectors
g_pfnVectors:
.word _estack
.word Reset_Handler
.word NMI_Handler
.word HardFault_Handler
/* ... device IRQ vectors from vendor CMSIS ... */
.section .text.Reset_Handler
.thumb_func
.global Reset_Handler
Reset_Handler:
ldr r0, =_sidata /* .data load address (LMA) */
ldr r1, =_sdata /* .data VMA start */
ldr r2, =_edata
b LoopCopyDataInit
CopyDataInit:
ldr r3, [r0], #4
str r3, [r1], #4
LoopCopyDataInit:
cmp r1, r2
blt CopyDataInit
ldr r2, =_sbss
ldr r4, =_ebss
movs r3, #0
b LoopFillZerobss
FillZerobss:
str r3, [r2], #4
LoopFillZerobss:
cmp r2, r4
blt FillZerobss
bl SystemInit
bl main
b .c
/* Linker symbols — declared extern in startup */
extern uint32_t _estack, _sidata, _sdata, _edata, _sbss, _ebss;3. VTOR relocation (Cortex-M)
c
#include "core_cm4.h" /* CMSIS */
void relocate_vector_table(uint32_t base) {
SCB->VTOR = base & 0xFFFFFF80U; /* must be aligned per ARM ref manual */
__DSB();
__ISB();
}Bootloader jumping to app often requires setting VTOR to the application's vector table address (e.g., 0x08020000 on STM32 flash).
4. RISC-V startup (overview)
asm
/* entry.S — simplified */
.section .text.entry
.global _start
_start:
la sp, _stack_top
la t0, _bss_start
la t1, _bss_end
clear_bss:
beq t0, t1, bss_done
sw zero, 0(t0)
addi t0, t0, 4
j clear_bss
bss_done:
call main
j .Trap vector: mtvec for M-mode; see skills/platform/riscv-privileged.
5. crt0 responsibilities
| Task | Who does it |
|---|---|
Copy .data LMA→VMA | Reset_Handler / crt0 |
Zero .bss | Reset_Handler |
| Init stack | Vector[0] or explicit sp |
Heap (_sbrk) | Optional; libc or custom |
| C++ constructors | __libc_init_array() if using full libc |
| FPU enable | SystemInit on Cortex-M4F/M7 |
6. Linker script integration
ld
_estack = ORIGIN(RAM) + LENGTH(RAM);
_sidata = LOADADDR(.data);Cross-link skills/embedded/linker-scripts for MEMORY/SECTIONS layout.
7. Agent usage examples
/baremetal-startup My STM32 never reaches main — what should Reset_Handler do?
/baremetal-startup How do I relocate the vector table after bootloader jump?Common Problems
| Symptom | Cause | Fix |
|---|---|---|
| HardFault immediately | Stack pointer invalid | Set _estack to valid RAM top |
| Globals wrong at boot | .data not copied | Copy LMA→VMA in Reset_Handler |
| BSS non-zero | .bss not zeroed | Add bss clear loop |
| IRQs don't fire | VTOR points to wrong table | SCB->VTOR = app_vector_addr |
main returns into garbage | No loop after main | while(1) or WFI loop |
| C++ static init crash | Constructors before clocks | Call SystemInit first |
Related Skills
skills/embedded/linker-scripts—_estack, LMA/VMA, section placementskills/baremetal/interrupts-and-exceptions-baremetal— vector table IRQ entriesskills/baremetal/bootloaders-embedded— VTOR relocation on app jumpskills/embedded/openocd-jtag— halt atReset_Handlerwith GDBskills/low-level-programming/assembly-arm— Thumb-2 syntaxskills/platform/riscv-privileged— RISC-V trap setup
