Merge pull request #1695 from cesanta/nucleo-f429zi-baremetal

Add baremetal example on Nucleo-F429ZI
2025-08-06 13:37:34 +08:00 · 2022-08-30 12:24:15 +01:00 · 2022-08-30 12:24:15 +01:00 · 229b7810df
commit 229b7810df
parent 0a265e79a6 42c1bee8ea
7 changed files with 651 additions and 0 deletions
--- a/examples/stm32/nucleo-f429zi-baremetal/Makefile
+++ b/examples/stm32/nucleo-f429zi-baremetal/Makefile
@ -0,0 +1,42 @@
+TARGET  = firmware
+ROOT    ?= $(realpath $(CURDIR)/../../..)
+D ?= docker
+DOCKER 	?= $(D) run --rm -v $(ROOT):$(ROOT) -w $(CURDIR) mdashnet/armgcc
+CROSS   ?= arm-none-eabi
+CFLAGS  ?=  -W -Wall -Wextra -Werror -Wundef -Wshadow -Wdouble-promotion \
+						-Wformat-truncation -fno-common -Wconversion \
+						-g3 -Os -ffunction-sections -fdata-sections -I. -I$(ROOT) \
+            -DMG_ARCH=MG_ARCH_NEWLIB -DMIP_DEBUG=1 -DMG_ENABLE_PACKED_FS=1 \
+						-DMG_ENABLE_CUSTOM_MILLIS=1 -DxMG_ENABLE_LINES=1 -DMG_ENABLE_MIP=1 \
+						-mcpu=cortex-m4 -mthumb -mfloat-abi=soft $(EXTRA_CFLAGS)
+LDFLAGS ?= -Tlink.ld -nostartfiles -nostdlib --specs nano.specs -lc -lgcc -Wl,--gc-sections -Wl,-Map=$@.map
+SOURCES = boot.c main.c syscalls.c \
+          $(ROOT)/mongoose.c \
+          $(ROOT)/examples/device-dashboard/packed_fs.c \
+          $(ROOT)/examples/device-dashboard/net.c
+
+all build example: $(TARGET).bin
+
+$(TARGET).bin: $(TARGET).elf
+	$(DOCKER) $(CROSS)-objcopy -O binary $< $@
+
+$(TARGET).elf: $(SOURCES) mcu.h
+	$(DOCKER) $(CROSS)-gcc $(SOURCES) $(CFLAGS) $(LDFLAGS) -o $@
+
+# Build on Windows. Download Win32 Zip from ARM GCC downloads, unzip to c:\armgcc
+ARMGCC ?= c:/armgcc
+windows: $(TARGET).bin
+windows: CROSS = $(ARMGCC)/bin/arm-none-eabi
+windows: DOCKER =
+
+# Show top 10 stack-hungry functions
+su: CFLAGS += -fstack-usage
+su: $(TARGET).elf
+	cat *.su | sort -rnk2 | head -10
+
+# Note: on "unknown chip id" flash error, wire BOOT0 to VDD and st-flash erase
+flash: $(TARGET).bin
+	st-flash --reset write $(TARGET).bin 0x8000000
+
+clean:
+	@rm -rf $(TARGET).* *.su
--- a/examples/stm32/nucleo-f429zi-baremetal/README.md
+++ b/examples/stm32/nucleo-f429zi-baremetal/README.md
@ -0,0 +1,36 @@
+# Baremetal webserver on NUCLEO-F429ZG
+
+This firmware uses experimental TCP/IP stack of the Mongoose Network Library,
+which implements the following:
+
+- Implements HTTP server and SNTP time synchronisation
+- No dependencies: no HAL, no CMSIS, no RTOS
+- Hand-written [mcu.h](mcu.h) header based on a [datasheet](https://www.st.com/resource/en/reference_manual/rm0090-stm32f405415-stm32f407417-stm32f427437-and-stm32f429439-advanced-armbased-32bit-mcus-stmicroelectronics.pdf)
+- Interrupt-driven [mip_driver_stm32.h](../../../drivers/mip_driver_stm32.h) ethernet driver
+- Blue LED blinky, based on SysTick interrupt
+- User button handler, turns off/on green LED, based on EXTI, interrupt-driven 
+- HardFault handler that blinks red LED
+- Debug log on UART3 (st-link)
+
+## Requirements
+
+- GNU make
+- [ARM GCC](https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm) toolchain for build
+- [st-link](https://github.com/stlink-org/stlink) for flashing
+
+## Usage
+
+Plugin your Nucleo board into USB, and attach an Ethernet cable.
+To build and flash:
+
+```sh
+$ make clean flash
+```
+
+To see debug log, use any serial monitor program like `picocom` at 115200 bps and configure it to insert carriage returns after line feeds:
+
+```sh
+$ picocom /dev/ttyACM0 -i -b 115200 --imap=lfcrlf
+```
+
+For more details and benchmark data on MIP, check the [F746ZG example](../nucleo-f746zg-baremetal/)
--- a/examples/stm32/nucleo-f429zi-baremetal/boot.c
+++ b/examples/stm32/nucleo-f429zi-baremetal/boot.c
@ -0,0 +1,162 @@
+// Copyright (c) 2022 Cesanta Software Limited
+// All rights reserved
+
+// Startup code
+__attribute__((naked, noreturn)) void _reset(void) {
+  // Init stack
+  asm("ldr sp, = _estack");
+
+  // Initialise memory
+  extern long _sbss, _ebss, _sdata, _edata, _sidata;
+  for (long *src = &_sbss; src < &_ebss; src++) *src = 0;
+  for (long *src = &_sdata, *dst = &_sidata; src < &_edata;) *src++ = *dst++;
+
+  // Call main()
+  extern void main(void);
+  main();
+  for (;;) (void) 0;
+}
+
+void __attribute__((weak)) DefaultIRQHandler(void) {
+  for (;;) (void) 0;
+}
+
+#define WEAK_ALIAS __attribute__((weak, alias("DefaultIRQHandler")))
+
+WEAK_ALIAS void NMI_Handler(void);
+WEAK_ALIAS void HardFault_Handler(void);
+WEAK_ALIAS void MemManage_Handler(void);
+WEAK_ALIAS void BusFault_Handler(void);
+WEAK_ALIAS void UsageFault_Handler(void);
+WEAK_ALIAS void SVC_Handler(void);
+WEAK_ALIAS void DebugMon_Handler(void);
+WEAK_ALIAS void PendSV_Handler(void);
+WEAK_ALIAS void SysTick_Handler(void);
+
+WEAK_ALIAS void WWDG_IRQHandler(void);
+WEAK_ALIAS void PVD_IRQHandler(void);
+WEAK_ALIAS void TAMP_STAMP_IRQHandler(void);
+WEAK_ALIAS void RTC_WKUP_IRQHandler(void);
+WEAK_ALIAS void FLASH_IRQHandler(void);
+WEAK_ALIAS void RCC_IRQHandler(void);
+WEAK_ALIAS void EXTI0_IRQHandler(void);
+WEAK_ALIAS void EXTI1_IRQHandler(void);
+WEAK_ALIAS void EXTI2_IRQHandler(void);
+WEAK_ALIAS void EXTI3_IRQHandler(void);
+WEAK_ALIAS void EXTI4_IRQHandler(void);
+WEAK_ALIAS void EXTI9_5_IRQHandler(void);
+WEAK_ALIAS void EXTI15_10_IRQHandler(void);
+WEAK_ALIAS void DMA1_Stream0_IRQHandler(void);
+WEAK_ALIAS void DMA1_Stream1_IRQHandler(void);
+WEAK_ALIAS void DMA1_Stream2_IRQHandler(void);
+WEAK_ALIAS void DMA1_Stream3_IRQHandler(void);
+WEAK_ALIAS void DMA1_Stream4_IRQHandler(void);
+WEAK_ALIAS void DMA1_Stream5_IRQHandler(void);
+WEAK_ALIAS void DMA1_Stream6_IRQHandler(void);
+WEAK_ALIAS void ADC_IRQHandler(void);
+WEAK_ALIAS void CAN1_TX_IRQHandler(void);
+WEAK_ALIAS void CAN1_RX0_IRQHandler(void);
+WEAK_ALIAS void CAN1_RX1_IRQHandler(void);
+WEAK_ALIAS void CAN1_SCE_IRQHandler(void);
+WEAK_ALIAS void TIM1_BRK_TIM9_IRQHandler(void);
+WEAK_ALIAS void TIM1_UP_TIM10_IRQHandler(void);
+WEAK_ALIAS void TIM1_TRG_COM_TIM11_IRQHandler(void);
+WEAK_ALIAS void TIM1_CC_IRQHandler(void);
+WEAK_ALIAS void TIM2_IRQHandler(void);
+WEAK_ALIAS void TIM3_IRQHandler(void);
+WEAK_ALIAS void TIM4_IRQHandler(void);
+WEAK_ALIAS void I2C1_EV_IRQHandler(void);
+WEAK_ALIAS void I2C1_ER_IRQHandler(void);
+WEAK_ALIAS void I2C2_EV_IRQHandler(void);
+WEAK_ALIAS void I2C2_ER_IRQHandler(void);
+WEAK_ALIAS void SPI1_IRQHandler(void);
+WEAK_ALIAS void SPI2_IRQHandler(void);
+WEAK_ALIAS void USART1_IRQHandler(void);
+WEAK_ALIAS void USART2_IRQHandler(void);
+WEAK_ALIAS void USART3_IRQHandler(void);
+WEAK_ALIAS void RTC_Alarm_IRQHandler(void);
+WEAK_ALIAS void OTG_FS_WKUP_IRQHandler(void);
+WEAK_ALIAS void TIM8_BRK_TIM12_IRQHandler(void);
+WEAK_ALIAS void TIM8_UP_TIM13_IRQHandler(void);
+WEAK_ALIAS void TIM8_TRG_COM_TIM14_IRQHandler(void);
+WEAK_ALIAS void TIM8_CC_IRQHandler(void);
+WEAK_ALIAS void DMA1_Stream7_IRQHandler(void);
+WEAK_ALIAS void FMC_IRQHandler(void);
+WEAK_ALIAS void SDMMC1_IRQHandler(void);
+WEAK_ALIAS void TIM5_IRQHandler(void);
+WEAK_ALIAS void SPI3_IRQHandler(void);
+WEAK_ALIAS void UART4_IRQHandler(void);
+WEAK_ALIAS void UART5_IRQHandler(void);
+WEAK_ALIAS void TIM6_DAC_IRQHandler(void);
+WEAK_ALIAS void TIM7_IRQHandler(void);
+WEAK_ALIAS void DMA2_Stream0_IRQHandler(void);
+WEAK_ALIAS void DMA2_Stream1_IRQHandler(void);
+WEAK_ALIAS void DMA2_Stream2_IRQHandler(void);
+WEAK_ALIAS void DMA2_Stream3_IRQHandler(void);
+WEAK_ALIAS void DMA2_Stream4_IRQHandler(void);
+WEAK_ALIAS void ETH_IRQHandler(void);
+WEAK_ALIAS void ETH_WKUP_IRQHandler(void);
+WEAK_ALIAS void CAN2_TX_IRQHandler(void);
+WEAK_ALIAS void CAN2_RX0_IRQHandler(void);
+WEAK_ALIAS void CAN2_RX1_IRQHandler(void);
+WEAK_ALIAS void CAN2_SCE_IRQHandler(void);
+WEAK_ALIAS void OTG_FS_IRQHandler(void);
+WEAK_ALIAS void DMA2_Stream5_IRQHandler(void);
+WEAK_ALIAS void DMA2_Stream6_IRQHandler(void);
+WEAK_ALIAS void DMA2_Stream7_IRQHandler(void);
+WEAK_ALIAS void USART6_IRQHandler(void);
+WEAK_ALIAS void I2C3_EV_IRQHandler(void);
+WEAK_ALIAS void I2C3_ER_IRQHandler(void);
+WEAK_ALIAS void OTG_HS_EP1_OUT_IRQHandler(void);
+WEAK_ALIAS void OTG_HS_EP1_IN_IRQHandler(void);
+WEAK_ALIAS void OTG_HS_WKUP_IRQHandler(void);
+WEAK_ALIAS void OTG_HS_IRQHandler(void);
+WEAK_ALIAS void DCMI_IRQHandler(void);
+WEAK_ALIAS void RNG_IRQHandler(void);
+WEAK_ALIAS void FPU_IRQHandler(void);
+WEAK_ALIAS void UART7_IRQHandler(void);
+WEAK_ALIAS void UART8_IRQHandler(void);
+WEAK_ALIAS void SPI4_IRQHandler(void);
+WEAK_ALIAS void SPI5_IRQHandler(void);
+WEAK_ALIAS void SPI6_IRQHandler(void);
+WEAK_ALIAS void SAI1_IRQHandler(void);
+WEAK_ALIAS void LTDC_IRQHandler(void);
+WEAK_ALIAS void LTDC_ER_IRQHandler(void);
+WEAK_ALIAS void DMA2D_IRQHandler(void);
+
+// IRQ table
+__attribute__((section(".vectors"))) void (*tab[16 + 91])(void) = {
+    // Cortex interrupts
+    0, _reset, NMI_Handler, HardFault_Handler, MemManage_Handler,
+    BusFault_Handler, UsageFault_Handler, 0, 0, 0, 0, SVC_Handler,
+    DebugMon_Handler, 0, PendSV_Handler, SysTick_Handler,
+
+    // Interrupts from peripherals
+    WWDG_IRQHandler, PVD_IRQHandler, TAMP_STAMP_IRQHandler, RTC_WKUP_IRQHandler,
+    FLASH_IRQHandler, RCC_IRQHandler, EXTI0_IRQHandler, EXTI1_IRQHandler,
+    EXTI2_IRQHandler, EXTI3_IRQHandler, EXTI4_IRQHandler,
+    DMA1_Stream0_IRQHandler, DMA1_Stream1_IRQHandler, DMA1_Stream2_IRQHandler,
+    DMA1_Stream3_IRQHandler, DMA1_Stream4_IRQHandler, DMA1_Stream5_IRQHandler,
+    DMA1_Stream6_IRQHandler, ADC_IRQHandler, CAN1_TX_IRQHandler,
+    CAN1_RX0_IRQHandler, CAN1_RX1_IRQHandler, CAN1_SCE_IRQHandler,
+    EXTI9_5_IRQHandler, TIM1_BRK_TIM9_IRQHandler, TIM1_UP_TIM10_IRQHandler,
+    TIM1_TRG_COM_TIM11_IRQHandler, TIM1_CC_IRQHandler, TIM2_IRQHandler,
+    TIM3_IRQHandler, TIM4_IRQHandler, I2C1_EV_IRQHandler, I2C1_ER_IRQHandler,
+    I2C2_EV_IRQHandler, I2C2_ER_IRQHandler, SPI1_IRQHandler, SPI2_IRQHandler,
+    USART1_IRQHandler, USART2_IRQHandler, USART3_IRQHandler,
+    EXTI15_10_IRQHandler, RTC_Alarm_IRQHandler, OTG_FS_WKUP_IRQHandler,
+    TIM8_BRK_TIM12_IRQHandler, TIM8_UP_TIM13_IRQHandler,
+    TIM8_TRG_COM_TIM14_IRQHandler, TIM8_CC_IRQHandler, DMA1_Stream7_IRQHandler,
+    FMC_IRQHandler, SDMMC1_IRQHandler, TIM5_IRQHandler, SPI3_IRQHandler,
+    UART4_IRQHandler, UART5_IRQHandler, TIM6_DAC_IRQHandler, TIM7_IRQHandler,
+    DMA2_Stream0_IRQHandler, DMA2_Stream1_IRQHandler, DMA2_Stream2_IRQHandler,
+    DMA2_Stream3_IRQHandler, DMA2_Stream4_IRQHandler, ETH_IRQHandler,
+    ETH_WKUP_IRQHandler, CAN2_TX_IRQHandler, CAN2_RX0_IRQHandler,
+    CAN2_RX1_IRQHandler, CAN2_SCE_IRQHandler, OTG_FS_IRQHandler,
+    DMA2_Stream5_IRQHandler, DMA2_Stream6_IRQHandler, DMA2_Stream7_IRQHandler,
+    USART6_IRQHandler, I2C3_EV_IRQHandler, I2C3_ER_IRQHandler,
+    OTG_HS_EP1_OUT_IRQHandler, OTG_HS_EP1_IN_IRQHandler, OTG_HS_WKUP_IRQHandler,
+    OTG_HS_IRQHandler, DCMI_IRQHandler, 0, RNG_IRQHandler, FPU_IRQHandler,
+    UART7_IRQHandler, UART8_IRQHandler, SPI4_IRQHandler, SPI5_IRQHandler,
+    SPI6_IRQHandler, SAI1_IRQHandler, LTDC_IRQHandler, LTDC_ER_IRQHandler,
+    DMA2D_IRQHandler};
--- a/examples/stm32/nucleo-f429zi-baremetal/link.ld
+++ b/examples/stm32/nucleo-f429zi-baremetal/link.ld
@ -0,0 +1,29 @@
+ENTRY(_reset);
+MEMORY {
+  flash(rx)  : ORIGIN = 0x08000000, LENGTH = 2048k
+  sram(rwx) : ORIGIN = 0x20000000, LENGTH = 192k  /* remaining 64k in a separate address space */
+}
+_estack     = ORIGIN(sram) + LENGTH(sram);    /* stack points to end of SRAM */
+
+SECTIONS {
+  .vectors  : { KEEP(*(.vectors)) }   > flash
+  .text     : { *(.text*) }           > flash
+  .rodata   : { *(.rodata*) }         > flash
+
+  .data : {
+    _sdata = .;   /* for init_ram() */
+    *(.first_data)
+    *(.data SORT(.data.*))
+    _edata = .;  /* for init_ram() */
+  } > sram AT > flash
+  _sidata = LOADADDR(.data);
+
+  .bss : {
+    _sbss = .;              /* for init_ram() */
+    *(.bss SORT(.bss.*) COMMON)
+    _ebss = .;              /* for init_ram() */
+  } > sram
+
+  . = ALIGN(8);
+  _end = .;     /* for cmsis_gcc.h and init_ram() */
+}
--- a/examples/stm32/nucleo-f429zi-baremetal/main.c
+++ b/examples/stm32/nucleo-f429zi-baremetal/main.c
@ -0,0 +1,82 @@
+// Copyright (c) 2022 Cesanta Software Limited
+// All rights reserved
+
+#include "mcu.h"
+#include "mongoose.h"
+
+#define LED1 PIN('B', 0)   // On-board LED pin (green)
+#define LED2 PIN('B', 7)   // On-board LED pin (blue)
+#define LED3 PIN('B', 14)  // On-board LED pin (red)
+#define BTN1 PIN('C', 13)  // On-board user button
+
+static uint64_t s_ticks, s_exti;  // Counters, increased by IRQ handlers
+
+static void blink_cb(void *arg) {  // Blink periodically
+  // MG_INFO(("ticks: %u", (unsigned) s_ticks));
+  gpio_toggle(LED2);
+  (void) arg;
+}
+
+uint64_t mg_millis(void) {  // Declare our own uptime function
+  return s_ticks;           // Return number of milliseconds since boot
+}
+
+void HardFault_Handler(void) {                // Escalated fault handler
+  gpio_output(LED3);                          // Setup red LED
+  for (;;) spin(2999999), gpio_toggle(LED3);  // Blink LED infinitely
+}
+
+void SysTick_Handler(void) {  // SyStick IRQ handler, triggered every 1ms
+  s_ticks++;
+}
+
+void EXTI15_10_IRQHandler(void) {  // External interrupt handler
+  s_exti++;
+  if (EXTI->PR & BIT(PINNO(BTN1))) EXTI->PR = BIT(PINNO(BTN1));
+  gpio_write(LED1, gpio_read(BTN1));  // No debounce. Turn LED if button pressed
+}
+
+int main(void) {
+  static struct uart *uart = UART3;  // Use UART3 - its attached to debug
+  clock_init();                      // Set clock to 180MHz
+  systick_init(FREQ / 1000);         // Increment s_ticks every ms
+  gpio_output(LED1);                 // Setup green LED
+  gpio_output(LED2);                 // Setup blue LED
+  gpio_input(BTN1);                  // Set button to input
+  irq_exti_attach(BTN1);             // Attach BTN1 to exti
+  uart_init(uart, 115200);           // It is wired to the debug port
+
+  // Initialise Ethernet. Enable MAC GPIO pins, see
+  // https://www.farnell.com/datasheets/2014265.pdf section 6.10
+  uint16_t pins[] = {PIN('A', 1),  PIN('A', 2),  PIN('A', 7),
+                     PIN('B', 13), PIN('C', 1),  PIN('C', 4),
+                     PIN('C', 5),  PIN('G', 11), PIN('G', 13)};
+  for (size_t i = 0; i < sizeof(pins) / sizeof(pins[0]); i++) {
+    gpio_init(pins[i], GPIO_MODE_AF, GPIO_OTYPE_PUSH_PULL, GPIO_SPEED_INSANE,
+              GPIO_PULL_NONE, 11);
+  }
+  nvic_enable_irq(61);                          // Setup Ethernet IRQ handler
+  RCC->APB2ENR |= BIT(14);                      // Enable SYSCFG
+  SYSCFG->PMC |= BIT(23);                       // Use RMII. Goes first!
+  RCC->AHB1ENR |= BIT(25) | BIT(26) | BIT(27);  // Enable Ethernet clocks
+  RCC->AHB1RSTR |= BIT(25);                     // ETHMAC force reset
+  RCC->AHB1RSTR &= ~BIT(25);                    // ETHMAC release reset
+
+  struct mg_mgr mgr;        // Initialise Mongoose event manager
+  mg_mgr_init(&mgr);        // and attach it to the MIP interface
+  mg_log_set(MG_LL_DEBUG);  // Set log level
+  mg_timer_add(&mgr, 500, MG_TIMER_REPEAT, blink_cb, &mgr);
+
+  // Initialise Mongoose network stack
+  // Specify MAC address, and use 0 for IP, mask, GW - i.e. use DHCP
+  // For static configuration, specify IP/mask/GW in network byte order
+  struct mip_ipcfg c = {.mac = {0, 0, 1, 2, 3, 4}, .ip = 0, .mask = 0, .gw = 0};
+  mip_init(&mgr, &c, &mip_driver_stm32, NULL);
+  MG_INFO(("Init done, starting main loop"));
+
+  extern void device_dashboard_fn(struct mg_connection *, int, void *, void *);
+  mg_http_listen(&mgr, "http://0.0.0.0", device_dashboard_fn, &mgr);
+  for (;;) mg_mgr_poll(&mgr, 0);  // Infinite event loop
+
+  return 0;
+}
--- a/examples/stm32/nucleo-f429zi-baremetal/mcu.h
+++ b/examples/stm32/nucleo-f429zi-baremetal/mcu.h
@ -0,0 +1,217 @@
+// Copyright (c) 2022 Cesanta Software Limited
+// All rights reserved
+// https://www.st.com/resource/en/reference_manual/dm00124865-stm32f75xxx-and-stm32f74xxx-advanced-arm-based-32-bit-mcus-stmicroelectronics.pdf
+
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+#define BIT(x) (1UL << (x))
+#define SETBITS(R, CLEARMASK, SETMASK) (R) = ((R) & ~(CLEARMASK)) | (SETMASK)
+#define PIN(bank, num) ((((bank) - 'A') << 8) | (num))
+#define PINNO(pin) (pin & 255)
+#define PINBANK(pin) (pin >> 8)
+
+/* System clock
+6.3.3: APB1 clock <= 45MHz; APB2 clock <= 90MHz
+3.5.1, Table 11: configure flash latency (WS) in accordance to clock freq
+33.4: The AHB clock frequency must be at least 25 MHz when the Ethernet controller is used */
+enum { APB1_PRE = 5 /* AHB clock / 4 */, APB2_PRE = 4 /* AHB clock / 2 */ };
+enum { PLL_HSI = 16, PLL_M = 8, PLL_N = 180, PLL_P = 2 };  // Run at 180 Mhz
+//#define PLL_FREQ PLL_HSI
+#define PLL_FREQ (PLL_HSI * PLL_N / PLL_M / PLL_P)
+#define FLASH_LATENCY 5 
+#define FREQ (PLL_FREQ * 1000000)
+
+static inline void spin(volatile uint32_t count) {
+  while (count--) asm("nop");
+}
+
+struct rcc {
+  volatile uint32_t CR, PLLCFGR, CFGR, CIR, AHB1RSTR, AHB2RSTR, AHB3RSTR,
+      RESERVED0, APB1RSTR, APB2RSTR, RESERVED1[2], AHB1ENR, AHB2ENR, AHB3ENR,
+      RESERVED2, APB1ENR, APB2ENR, RESERVED3[2], AHB1LPENR, AHB2LPENR,
+      AHB3LPENR, RESERVED4, APB1LPENR, APB2LPENR, RESERVED5[2], BDCR, CSR,
+      RESERVED6[2], SSCGR, PLLI2SCFGR;
+};
+#define RCC ((struct rcc *) 0x40023800)
+
+struct pwr {
+  volatile uint32_t CR, CSR;
+};
+#define PWR ((struct pwr *) 0x40007000)
+
+struct nvic {
+  volatile uint32_t ISER[8], RESERVED0[24], ICER[8], RSERVED1[24], ISPR[8],
+      RESERVED2[24], ICPR[8], RESERVED3[24], IABR[8], RESERVED4[56], IP[240],
+      RESERVED5[644], STIR;
+};
+#define NVIC ((struct nvic *) 0xe000e100)
+static inline void nvic_set_prio(int irq, uint32_t prio) {
+  NVIC->IP[irq] = prio << 4;
+}
+static inline void nvic_enable_irq(int irq) {
+  NVIC->ISER[irq >> 5] = (uint32_t) (1 << (irq & 31));
+}
+
+struct systick {
+  volatile uint32_t CTRL, LOAD, VAL, CALIB;
+};
+#define SYSTICK ((struct systick *) 0xe000e010)  // 2.2.2
+static inline void systick_init(uint32_t ticks) {
+  if ((ticks - 1) > 0xffffff) return;  // Systick timer is 24 bit
+  SYSTICK->LOAD = ticks - 1;
+  SYSTICK->VAL = 0;
+  SYSTICK->CTRL = BIT(0) | BIT(1) | BIT(2);  // Enable systick
+  RCC->APB2ENR |= BIT(14);                   // Enable SYSCFG
+}
+
+struct flash {
+  volatile uint32_t ACR, KEYR, OPTKEYR, SR, CR, AR, RESERVED, OBR, WRPR;
+};
+#define FLASH ((struct flash *) 0x40023c00)
+
+struct scb {
+  volatile uint32_t CPUID, ICSR, VTOR, AIRCR, SCR, CCR, SHPR[3], SHCSR, CFSR,
+      HFSR, DFSR, MMFAR, BFAR, AFSR, ID_PFR[2], ID_DFR, ID_AFR, ID_MFR[4],
+      ID_ISAR[5], RESERVED0[1], CLIDR, CTR, CCSIDR, CSSELR, CPACR,
+      RESERVED3[93], STIR, RESERVED4[15], MVFR0, MVFR1, MVFR2, RESERVED5[1],
+      ICIALLU, RESERVED6[1], ICIMVAU, DCIMVAC, DCISW, DCCMVAU, DCCMVAC, DCCSW,
+      DCCIMVAC, DCCISW, RESERVED7[6], ITCMCR, DTCMCR, AHBPCR, CACR, AHBSCR,
+      RESERVED8[1], ABFSR;
+};
+#define SCB ((struct scb *) 0xe000e000)
+
+enum { GPIO_MODE_INPUT, GPIO_MODE_OUTPUT, GPIO_MODE_AF, GPIO_MODE_ANALOG };
+enum { GPIO_OTYPE_PUSH_PULL, GPIO_OTYPE_OPEN_DRAIN };
+enum { GPIO_SPEED_LOW, GPIO_SPEED_MEDIUM, GPIO_SPEED_HIGH, GPIO_SPEED_INSANE };
+enum { GPIO_PULL_NONE, GPIO_PULL_UP, GPIO_PULL_DOWN };
+
+struct gpio {
+  volatile uint32_t MODER, OTYPER, OSPEEDR, PUPDR, IDR, ODR, BSRR, LCKR, AFR[2];
+};
+#define GPIO(N) ((struct gpio *) (0x40020000 + 0x400 * (N)))
+
+static struct gpio *gpio_bank(uint16_t pin) {
+  return GPIO(PINBANK(pin));
+}
+static inline void gpio_toggle(uint16_t pin) {
+  struct gpio *gpio = gpio_bank(pin);
+  uint32_t mask = BIT(PINNO(pin));
+  gpio->BSRR |= mask << (gpio->ODR & mask ? 16 : 0);
+}
+static inline int gpio_read(uint16_t pin) {
+  return gpio_bank(pin)->IDR & BIT(PINNO(pin)) ? 1 : 0;
+}
+static inline void gpio_write(uint16_t pin, bool val) {
+  struct gpio *gpio = gpio_bank(pin);
+  gpio->BSRR |= BIT(PINNO(pin)) << (val ? 0 : 16);
+}
+static inline void gpio_init(uint16_t pin, uint8_t mode, uint8_t type,
+                             uint8_t speed, uint8_t pull, uint8_t af) {
+  struct gpio *gpio = gpio_bank(pin);
+  uint8_t n = (uint8_t) (PINNO(pin));
+  RCC->AHB1ENR |= BIT(PINBANK(pin));  // Enable GPIO clock
+  SETBITS(gpio->OTYPER, 1UL << n, ((uint32_t) type) << n);
+  SETBITS(gpio->OSPEEDR, 3UL << (n * 2), ((uint32_t) speed) << (n * 2));
+  SETBITS(gpio->PUPDR, 3UL << (n * 2), ((uint32_t) pull) << (n * 2));
+  SETBITS(gpio->AFR[n >> 3], 15UL << ((n & 7) * 4),
+          ((uint32_t) af) << ((n & 7) * 4));
+  SETBITS(gpio->MODER, 3UL << (n * 2), ((uint32_t) mode) << (n * 2));
+}
+static inline void gpio_input(uint16_t pin) {
+  gpio_init(pin, GPIO_MODE_INPUT, GPIO_OTYPE_PUSH_PULL, GPIO_SPEED_HIGH,
+            GPIO_PULL_NONE, 0);
+}
+static inline void gpio_output(uint16_t pin) {
+  gpio_init(pin, GPIO_MODE_OUTPUT, GPIO_OTYPE_PUSH_PULL, GPIO_SPEED_HIGH,
+            GPIO_PULL_NONE, 0);
+}
+
+struct syscfg {
+  volatile uint32_t MEMRMP, PMC, EXTICR[4], RESERVED[2], CMPCR;
+};
+#define SYSCFG ((struct syscfg *) 0x40013800)
+
+struct exti {
+  volatile uint32_t IMR, EMR, RTSR, FTSR, SWIER, PR;
+};
+#define EXTI ((struct exti *) 0x40013c00)
+
+static inline void irq_exti_attach(uint16_t pin) {
+  uint8_t bank = (uint8_t) (PINBANK(pin)), n = (uint8_t) (PINNO(pin));
+  RCC->APB2ENR |= BIT(14);  // Enable SYSCFG
+  SYSCFG->EXTICR[n / 4] &= ~(15UL << ((n % 4) * 4));
+  SYSCFG->EXTICR[n / 4] |= (uint32_t) (bank << ((n % 4) * 4));
+  EXTI->IMR |= BIT(n);
+  EXTI->RTSR |= BIT(n);
+  EXTI->FTSR |= BIT(n);
+  int irqvec = n < 5 ? 6 + n : n < 10 ? 23 : 40;  // IRQ vector index, 10.1.2
+  nvic_set_prio(irqvec, 3);
+  nvic_enable_irq(irqvec);
+}
+
+struct uart {
+  volatile uint32_t SR, DR, BRR, CR1, CR2, CR3, GTPR;
+};
+#define UART1 ((struct uart *) 0x40011000)
+#define UART2 ((struct uart *) 0x40004400)
+#define UART3 ((struct uart *) 0x40004800)
+
+static inline void uart_init(struct uart *uart, unsigned long baud) {
+  // https://www.st.com/resource/en/datasheet/stm32f429zi.pdf
+  uint8_t af = 0;           // Alternate function
+  uint16_t rx = 0, tx = 0;  // pins
+
+  if (uart == UART1) RCC->APB2ENR |= BIT(4);
+  if (uart == UART2) RCC->APB1ENR |= BIT(17);
+  if (uart == UART3) RCC->APB1ENR |= BIT(18);
+
+  if (uart == UART1) af = 4, tx = PIN('A', 9), rx = PIN('A', 10);
+  if (uart == UART2) af = 4, tx = PIN('A', 2), rx = PIN('A', 3);
+  if (uart == UART3) af = 7, tx = PIN('D', 8), rx = PIN('D', 9);
+
+  gpio_init(tx, GPIO_MODE_AF, GPIO_OTYPE_PUSH_PULL, GPIO_SPEED_HIGH, 0, af);
+  gpio_init(rx, GPIO_MODE_AF, GPIO_OTYPE_PUSH_PULL, GPIO_SPEED_HIGH, 0, af);
+  uart->CR1 = 0;                          // Disable this UART
+  uart->BRR = FREQ / 4 / baud;      // Baud rate x16 (with 4dp), "4" is APBx prescaler, different from APBx_PRE
+                                    // TODO(): make this configurable ?
+  uart->CR1 |= BIT(13) | BIT(2) | BIT(3);  // Set UE, RE, TE
+}
+static inline void uart_write_byte(struct uart *uart, uint8_t byte) {
+  uart->DR = byte;
+  while ((uart->SR & BIT(7)) == 0) spin(1);
+}
+static inline void uart_write_buf(struct uart *uart, char *buf, size_t len) {
+  while (len-- > 0) uart_write_byte(uart, *(uint8_t *) buf++);
+}
+static inline int uart_read_ready(struct uart *uart) {
+  return uart->SR & BIT(5);  // If RXNE bit is set, data is ready
+}
+static inline uint8_t uart_read_byte(struct uart *uart) {
+  return (uint8_t) (uart->DR & 255);
+}
+
+static inline void clock_init(void) {  // Set clock frequency
+#if 0
+  RCC->APB1ENR |= BIT(28);                     // Power enable
+  PWR->CR |= 3UL << 14;                       // Voltage regulator scale 3
+  PWR->CR |= BIT(16);                         // Enable overdrive
+  while ((PWR->CSR & BIT(16)) == 0) spin(1);  // Wait until done
+  PWR->CR |= BIT(17);                         // Enable overdrive switching
+  while ((PWR->CSR & BIT(17)) == 0) spin(1);  // Wait until done
+  SCB->CPACR |= ((3UL << 10 * 2) | (3UL << 11 * 2));  // Enable FPU
+#endif
+  FLASH->ACR |= FLASH_LATENCY | BIT(8) | BIT(9);    // Flash latency, prefetch, Icache, Dcache
+  RCC->PLLCFGR &= ~((BIT(17) - 1));                 // Clear PLL multipliers
+  RCC->PLLCFGR |= (((PLL_P - 2) / 2) & 3) << 16;    // Set PLL_P
+  RCC->PLLCFGR |= PLL_M | (PLL_N << 6);             // Set PLL_M and PLL_N
+  RCC->CR |= BIT(24);                               // Enable PLL
+  while ((RCC->CR & BIT(25)) == 0) spin(1);         // Wait until done
+  RCC->CFGR = (APB1_PRE << 10) | (APB2_PRE << 13);  // Set prescalers
+  RCC->CFGR |= 2;                                   // Set clock source to PLL
+  while ((RCC->CFGR & 12) == 0) spin(1);            // Wait until done
+}
--- a/examples/stm32/nucleo-f429zi-baremetal/syscalls.c
+++ b/examples/stm32/nucleo-f429zi-baremetal/syscalls.c
@ -0,0 +1,83 @@
+#include <sys/stat.h>
+
+#include "mcu.h"
+
+int _fstat(int fd, struct stat *st) {
+  if (fd < 0) return -1;
+  st->st_mode = S_IFCHR;
+  return 0;
+}
+
+void *_sbrk(int incr) {
+  extern char _end;
+  static unsigned char *heap = NULL;
+  unsigned char *prev_heap;
+  if (heap == NULL) heap = (unsigned char *) &_end;
+  prev_heap = heap;
+  heap += incr;
+  return prev_heap;
+}
+
+int _open(const char *path) {
+  (void) path;
+  return -1;
+}
+
+int _close(int fd) {
+  (void) fd;
+  return -1;
+}
+
+int _isatty(int fd) {
+  (void) fd;
+  return 1;
+}
+
+int _lseek(int fd, int ptr, int dir) {
+  (void) fd, (void) ptr, (void) dir;
+  return 0;
+}
+
+void _exit(int status) {
+  (void) status;
+  for (;;) asm volatile("BKPT #0");
+}
+
+void _kill(int pid, int sig) {
+  (void) pid, (void) sig;
+}
+
+int _getpid(void) {
+  return -1;
+}
+
+int _write(int fd, char *ptr, int len) {
+  (void) fd, (void) ptr, (void) len;
+  if (fd == 1) uart_write_buf(UART3, ptr, (size_t) len);
+  return -1;
+}
+
+int _read(int fd, char *ptr, int len) {
+  (void) fd, (void) ptr, (void) len;
+  return -1;
+}
+
+int _link(const char *a, const char *b) {
+  (void) a, (void) b;
+  return -1;
+}
+
+int _unlink(const char *a) {
+  (void) a;
+  return -1;
+}
+
+int _stat(const char *path, struct stat *st) {
+  (void) path, (void) st;
+  return -1;
+}
+
+int mkdir(const char *path, mode_t mode) {
+  (void) path, (void) mode;
+  return -1;
+}