bootloaders-embedded

Name: bootloaders-embedded
Author: mohitmishra786

141stars19forks

How to install bootloaders-embedded?

mohitmishra786/low-level-dev-skills/bootloaders-embedded

$npx -y skills add mohitmishra786/low-level-dev-skills --skill bootloaders-embedded

Installs into the current project.

Summary

Embedded bootloader skill for firmware update and app handoff. Use when writing a custom bootloader, jumping to application code, relocating VTOR, or implementing DFU/USB firmware update on Cortex-M. Activates on queries about bootloader jump, vector table relocation, application

Files · 1

View on GitHub

SKILL.md

1	# Embedded Bootloaders
2
3	## Purpose
4
5	Guide agents through embedded bootloader fundamentals: vector table relocation, safe handoff from bootloader to application, flash partitioning, and basic firmware-update patterns (UART, USB DFU, or custom protocol) on Cortex-M and similar MCUs.
6
7	## When to Use
8
9	- Application must run at non-zero flash offset (e.g. `0x08010000`)
10	- Implementing OTA or USB DFU without vendor HAL
11	- Debugging "app works when flashed alone but not via bootloader"
12	- Integrating with `skills/baremetal/baremetal-startup` and `skills/baremetal/stm32-baremetal`
13
14	## Workflow
15
16	### 1. Memory layout (typical STM32)
17
18	\| Region \| Address \| Size \| Content \|
19	\|--------\|---------\|------\|---------\|
20	\| Bootloader \| `0x08000000` \| 16–64 KB \| BL code, update logic \|
21	\| Application \| `0x08010000` \| remainder \| App vector + code \|
22
23	Linker script for app must set `FLASH ORIGIN` to app base; vector table must live at app base.
24
25	### 2. Valid application image check
26
27	Before jump, verify:
28
29	```
30	App vector[0] (initial SP) points into RAM region
31	App vector[1] (Reset) points into flash region and has Thumb bit set (LSB=1)
32	Optional: CRC or magic word in app metadata section
33	```
34
35	```c
36	#define APP_BASE 0x08010000U
37
38	static int app_valid(uint32_t base)
39	{
40	uint32_t sp = (uint32_t )base;
41	uint32_t reset = (uint32_t )(base + 4);
42	if (sp < SRAM_BASE \|\| sp > SRAM_END)
43	return 0;
44	if ((reset & 1U) == 0U)
45	return 0;
46	if (reset < base \|\| reset > FLASH_END)
47	return 0;
48	return 1;
49	}
50	```
51
52	### 3. Cortex-M handoff sequence
53
54	```c
55	typedef void (*app_entry_t)(void);
56
57	void jump_to_app(uint32_t app_base)
58	{
59	uint32_t sp = (uint32_t )app_base;
60	uint32_t reset = (uint32_t )(app_base + 4);
61
62	/* Disable interrupts and de-init peripherals/boot-owned hardware */
63	__disable_irq();
64	SysTick->CTRL = 0;
65	for (int i = 0; i < 8; i++) {
66	NVIC->ICER[i] = 0xFFFFFFFFU;
67	NVIC->ICPR[i] = 0xFFFFFFFFU;
68	}
69
70	SCB->VTOR = app_base;
71	__set_MSP(sp);
72	__DSB();
73	__ISB();
74
75	app_entry_t entry = (app_entry_t)reset;
76	entry(); /* does not return */
77	}
78	```
79
80	Application must set `SCB->VTOR = APP_BASE` early in `Reset_Handler` if startup assumes relocatable vector table.
81
82	### 4. Bootloader responsibilities
83
84	```
85	Power-on
86	├── Init minimal clock + UART/USB for update
87	├── Check update flag in RTC backup / GPIO strap
88	├── If update requested → receive image, verify, program flash
89	└── Else if valid app → jump_to_app()
90	└── Else stay in bootloader shell
91	```
92
93	### 5. STM32 system memory DFU (factory ROM)
94
95	STM32 chips expose USB DFU in system memory when BOOT0=1. Custom bootloaders are separate — do not confuse ROM DFU with user flash BL.
96
97	### 6. Update safety
98
99	- Write to scratch sector, verify CRC, then swap metadata pointer (A/B)
100	- Never erase the only valid image without recovery path
101	- Reset watchdog only after verified commit
102
103	### 7. Agent usage
104
105	```
106	/bootloaders-embedded Write STM32F4 jump-to-app at 0x08010000 with VTOR setup
107	```
108
109	## Common Problems
110
111	\| Symptom \| Cause \| Fix \|
112	\|---------\|-------\|-----\|
113	\| HardFault after jump \| SP invalid or Thumb bit missing \| Validate vectors; ensure `reset \\| 1` \|
114	\| IRQs hit bootloader handlers \| VTOR not relocated \| Set `SCB->VTOR` before enabling IRQs \|
115	\| App OK standalone, fails via BL \| Linker still at `0x08000000` \| Relink app with correct ORIGIN \|
116	\| UART garbage after jump \| BL left UART running \| De-init or reset peripherals \|
117	\| Brick after OTA \| Power loss mid-erase \| Dual-bank or metadata rollback \|
118
119	## Related Skills
120
121	- `skills/baremetal/baremetal-startup` — vector table and Reset_Handler
122	- `skills/baremetal/stm32-baremetal` — flash map and CMSIS
123	- `skills/baremetal/interrupts-and-exceptions-baremetal` — NVIC disable pattern
124	- `skills/embedded/linker-scripts` — VMA/LMA for split images
125	- `skills/embedded/openocd-jtag` — recover bricked flash

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Type

bootloaders-embedded

141stars19forks

View on GitHub

How to install bootloaders-embedded?

mohitmishra786/low-level-dev-skills/bootloaders-embedded

$npx -y skills add mohitmishra786/low-level-dev-skills --skill bootloaders-embedded

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Embedded Bootloaders
2
3	## Purpose
4
5	Guide agents through embedded bootloader fundamentals: vector table relocation, safe handoff from bootloader to application, flash partitioning, and basic firmware-update patterns (UART, USB DFU, or custom protocol) on Cortex-M and similar MCUs.
6
7	## When to Use
8
9	- Application must run at non-zero flash offset (e.g. `0x08010000`)
10	- Implementing OTA or USB DFU without vendor HAL
11	- Debugging "app works when flashed alone but not via bootloader"
12	- Integrating with `skills/baremetal/baremetal-startup` and `skills/baremetal/stm32-baremetal`
13
14	## Workflow
15
16	### 1. Memory layout (typical STM32)
17
18	\| Region \| Address \| Size \| Content \|
19	\|--------\|---------\|------\|---------\|
20	\| Bootloader \| `0x08000000` \| 16–64 KB \| BL code, update logic \|
21	\| Application \| `0x08010000` \| remainder \| App vector + code \|
22
23	Linker script for app must set `FLASH ORIGIN` to app base; vector table must live at app base.
24
25	### 2. Valid application image check
26
27	Before jump, verify:
28
29	```
30	App vector[0] (initial SP) points into RAM region
31	App vector[1] (Reset) points into flash region and has Thumb bit set (LSB=1)
32	Optional: CRC or magic word in app metadata section
33	```
34
35	```c
36	#define APP_BASE 0x08010000U
37
38	static int app_valid(uint32_t base)
39	{
40	uint32_t sp = (uint32_t )base;
41	uint32_t reset = (uint32_t )(base + 4);
42	if (sp < SRAM_BASE \|\| sp > SRAM_END)
43	return 0;
44	if ((reset & 1U) == 0U)
45	return 0;
46	if (reset < base \|\| reset > FLASH_END)
47	return 0;
48	return 1;
49	}
50	```
51
52	### 3. Cortex-M handoff sequence
53
54	```c
55	typedef void (*app_entry_t)(void);
56
57	void jump_to_app(uint32_t app_base)
58	{
59	uint32_t sp = (uint32_t )app_base;
60	uint32_t reset = (uint32_t )(app_base + 4);
61
62	/* Disable interrupts and de-init peripherals/boot-owned hardware */
63	__disable_irq();
64	SysTick->CTRL = 0;
65	for (int i = 0; i < 8; i++) {
66	NVIC->ICER[i] = 0xFFFFFFFFU;
67	NVIC->ICPR[i] = 0xFFFFFFFFU;
68	}
69
70	SCB->VTOR = app_base;
71	__set_MSP(sp);
72	__DSB();
73	__ISB();
74
75	app_entry_t entry = (app_entry_t)reset;
76	entry(); /* does not return */
77	}
78	```
79
80	Application must set `SCB->VTOR = APP_BASE` early in `Reset_Handler` if startup assumes relocatable vector table.
81
82	### 4. Bootloader responsibilities
83
84	```
85	Power-on
86	├── Init minimal clock + UART/USB for update
87	├── Check update flag in RTC backup / GPIO strap
88	├── If update requested → receive image, verify, program flash
89	└── Else if valid app → jump_to_app()
90	└── Else stay in bootloader shell
91	```
92
93	### 5. STM32 system memory DFU (factory ROM)
94
95	STM32 chips expose USB DFU in system memory when BOOT0=1. Custom bootloaders are separate — do not confuse ROM DFU with user flash BL.
96
97	### 6. Update safety
98
99	- Write to scratch sector, verify CRC, then swap metadata pointer (A/B)
100	- Never erase the only valid image without recovery path
101	- Reset watchdog only after verified commit
102
103	### 7. Agent usage
104
105	```
106	/bootloaders-embedded Write STM32F4 jump-to-app at 0x08010000 with VTOR setup
107	```
108
109	## Common Problems
110
111	\| Symptom \| Cause \| Fix \|
112	\|---------\|-------\|-----\|
113	\| HardFault after jump \| SP invalid or Thumb bit missing \| Validate vectors; ensure `reset \\| 1` \|
114	\| IRQs hit bootloader handlers \| VTOR not relocated \| Set `SCB->VTOR` before enabling IRQs \|
115	\| App OK standalone, fails via BL \| Linker still at `0x08000000` \| Relink app with correct ORIGIN \|
116	\| UART garbage after jump \| BL left UART running \| De-init or reset peripherals \|
117	\| Brick after OTA \| Power loss mid-erase \| Dual-bank or metadata rollback \|
118
119	## Related Skills
120
121	- `skills/baremetal/baremetal-startup` — vector table and Reset_Handler
122	- `skills/baremetal/stm32-baremetal` — flash map and CMSIS
123	- `skills/baremetal/interrupts-and-exceptions-baremetal` — NVIC disable pattern
124	- `skills/embedded/linker-scripts` — VMA/LMA for split images
125	- `skills/embedded/openocd-jtag` — recover bricked flash

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6 picks

Type