Pull CMSIS headers from github

README.md

@@ -1315,26 +1315,23 @@ CMSIS is an ARM standard, and since CMSIS headers are supplied by the MCU
 vendor, they are the source of authority. Therefore, using vendor
 headers is a preferred way, rather than writing definitions manually.
 
-In this section, we will replace our API functions in the `mcu.h` by the
-CMSIS vendor header, and leave the rest of the firmware intact.
-
-STM32 CMSIS headers for F4 family can be found at
-https://github.com/STMicroelectronics/cmsis_device_f4 repo. From there,
-copy the following files into our firmware directory,
-[step-5-cmsis](step-5-cmsis):
-- [stm32f429xx.h](https://raw.githubusercontent.com/STMicroelectronics/cmsis_device_f4/master/Include/stm32f429xx.h)
-- [system_stm32f4xx.h](https://raw.githubusercontent.com/STMicroelectronics/cmsis_device_f4/master/Include/system_stm32f4xx.h)
-
-Those two files depend on a standard ARM CMSIS includes, download them too:
-- [core_cm4.h](https://raw.githubusercontent.com/STMicroelectronics/STM32CubeF4/master/Drivers/CMSIS/Core/Include/core_cm4.h)
-- [cmsis_gcc.h](https://raw.githubusercontent.com/STMicroelectronics/STM32CubeF4/master/Drivers/CMSIS/Core/Include/cmsis_gcc.h)
-- [cmsis_version.h](https://raw.githubusercontent.com/STMicroelectronics/STM32CubeF4/master/Drivers/CMSIS/Core/Include/cmsis_version.h)
-- [cmsis_compiler.h](https://raw.githubusercontent.com/STMicroelectronics/STM32CubeF4/master/Drivers/CMSIS/Core/Include/cmsis_compiler.h)
-- [mpu_armv7.h](https://raw.githubusercontent.com/STMicroelectronics/STM32CubeF4/master/Drivers/CMSIS/Core/Include/mpu_armv7.h)
-
-From the `mcu.h`, remove all peripheral API and definitions, and leave only
-standard C inludes, vendor CMSIS include, defines to PIN, BIT, FREQ, and
-`timer_expired()` helper function:
+There are two sets of CMSIS headers:
+- First, there are ARM Core CMSIS headers. They describe ARM core,
+  and published by ARM on github: https://github.com/ARM-software/CMSIS_5
+- Second, there are MCU vendor CMSIS headers. They describe MCU peripherals,
+  and published by the MCU vendor. In our case, ST publishes them at
+  https://github.com/STMicroelectronics/cmsis_device_f4
+
+We can pull those headers by a simple Makefile snippet:
+
+The ST CMSIS package also provides startup files for all their MCUs. We
+can use those instead of hand-writing the startup.c. The ST-provided startup
+file calls `SystemInit()` function, so we define it in the `main.c`.
+
+Now, let's replace our API functions in the `mcu.h` using CMSIS definitions,
+and leave the rest of the firmware intact.  From the `mcu.h`, remove all
+peripheral API and definitions, and leave only standard C inludes, vendor CMSIS
+include, defines to PIN, BIT, FREQ, and `timer_expired()` helper function:
 
 ```c
 #pragma once
@@ -1366,38 +1363,12 @@ If we try to rebuild the firmware - `make clean build`, then GCC will fail
 complaining about missing `systick_init()`, `GPIO_MODE_OUTPUT`, `uart_init()`,
 and `UART3`. Let's add those using STM32 CMSIS files.
 
-Let's start from `systick_init()`. The `core_cm4.h` header defines
-`SysTick_Type` structure which is identical to our `struct systick`, and has
-an appropriate #define for `SysTick` peripheral. Also, `stm32f429xx.h` has
-a `RCC_TypeDef` structure and appropriate #define for the `RCC`. Therefore
-our `systick_init()` function remains almost unchanged: we only have to replace
-`SYSTICK` with `SysTick`:
-
-```c
-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
-}
-```
+Let's start from `systick_init()`. ARM core CMSIS headers provide a
+`SysTick_Config()` function that does the same - so we'll use it.
 
 Next goes `gpio_set_mode()` function. The  `stm32f429xx.h` header has
 `GPIO_TypeDef` structure, identical to our `struct gpio`. Let's use it:
-
-```c
-#define GPIO(bank) ((GPIO_TypeDef *) (GPIOA_BASE + 0x400 * (bank)))
-enum { GPIO_MODE_INPUT, GPIO_MODE_OUTPUT, GPIO_MODE_AF, GPIO_MODE_ANALOG };
-
-static inline void gpio_set_mode(uint16_t pin, uint8_t mode) {
-  GPIO_TypeDef *gpio = GPIO(PINBANK(pin));  // GPIO bank
-  int n = PINNO(pin);                      // Pin number
-  RCC->AHB1ENR |= BIT(PINBANK(pin));       // Enable GPIO clock
-  gpio->MODER &= ~(3U << (n * 2));         // Clear existing setting
-  gpio->MODER |= (mode & 3) << (n * 2);    // Set new mode
-}
-```
+https://github.com/cpq/bare-metal-programming-guide/blob/2a61ea23e44c4531b66f6508238cfc43ca7c2634/step-5-cmsis/mcu.h#L32-L41
 
 The `gpio_set_af()` and `gpio_write()` functions is also trivial -
 simply replace `struct gpio` with `GPIO_TypeDef`, and that's all.
@@ -1419,15 +1390,11 @@ shows the output. Congratulations, we have adopted our firmware code to
 use vendor CMSIS header files. Now let's reorganise the repository a bit
 by moving all standard files into `include` directory and updating Makefile
 to let GCC know about it:
+https://github.com/cpq/bare-metal-programming-guide/blob/2a61ea23e44c4531b66f6508238cfc43ca7c2634/step-5-cmsis/Makefile#L3
 
-```make
-...
-  -g3 -Os -ffunction-sections -fdata-sections -I. -Iinclude \
-```
-
-We have left with
-a project template that can be reused for the future projects.
-A complete project source code you can find in [step-5-cmsis](step-5-cmsis)
+We have left with a project template that can be reused for the future
+projects.  A complete project source code you can find in
+[step-5-cmsis](step-5-cmsis)
 
 
 ## Setting up clocks

step-5-cmsis/Makefile

@@ -1,26 +1,34 @@
 CFLAGS  ?=  -W -Wall -Wextra -Werror -Wundef -Wshadow -Wdouble-promotion \
             -Wformat-truncation -fno-common -Wconversion \
-            -g3 -Os -ffunction-sections -fdata-sections -I. -Iinclude \
+            -g3 -Os -ffunction-sections -fdata-sections \
+            -I. -Iinclude -Icmsis_core/CMSIS/Core/Include -Icmsis_f4/Include \
             -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16 $(EXTRA_CFLAGS)
 LDFLAGS ?= -Tlink.ld -nostartfiles -nostdlib --specs nano.specs -lc -lgcc -Wl,--gc-sections -Wl,-Map=$@.map
-SOURCES = main.c startup.c syscalls.c
+SOURCES = main.c syscalls.c
+SOURCES += cmsis_f4/Source/Templates/gcc/startup_stm32f429xx.s # ST startup file. Compiler-dependent!
 
 ifeq ($(OS),Windows_NT)
   RM = cmd /C del /Q /F
 else
-  RM = rm -f
+  RM = rm -rf
 endif
 
 build: firmware.bin
 
-firmware.elf: $(SOURCES)
-	arm-none-eabi-gcc $(SOURCES) $(CFLAGS) $(LDFLAGS) -o $@
+firmware.elf: cmsis_core cmsis_f4 mcu.h link.ld Makefile $(SOURCES) 
+	arm-none-eabi-gcc $(SOURCES) $(CFLAGS) $(CFLAGS_EXTRA) $(LDFLAGS) -o $@
 
 firmware.bin: firmware.elf
 	arm-none-eabi-objcopy -O binary $< $@
 
 flash: firmware.bin
 	st-flash --reset write $< 0x8000000
 
+cmsis_core:
+	git clone --depth 1 -b 5.9.0 https://github.com/ARM-software/CMSIS_5 $@
+
+cmsis_f4:
+	git clone --depth 1 -b v2.6.8 https://github.com/STMicroelectronics/cmsis_device_f4 $@
+
 clean:
-	$(RM) firmware.*
+	$(RM) firmware.* cmsis_*

step-5-cmsis/link.ld

@@ -1,29 +1,25 @@
-ENTRY(_reset);
+ENTRY(Reset_Handler);
 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
+  .vectors  : { KEEP(*(.isr_vector)) }   > flash
+  .text     : { *(.text*) }              > flash
+  .rodata   : { *(.rodata*) }            > flash
 
   .data : {
-    _sdata = .;   /* .data section start */
+    _sdata = .;
     *(.first_data)
     *(.data SORT(.data.*))
-    _edata = .;  /* .data section end */
+    _edata = .;
   } > sram AT > flash
   _sidata = LOADADDR(.data);
 
-  .bss : {
-    _sbss = .;              /* .bss section start */
-    *(.bss SORT(.bss.*) COMMON)
-    _ebss = .;              /* .bss section end */
-  } > sram
+  .bss : { _sbss = .; *(.bss SORT(.bss.*) COMMON) _ebss = .; } > sram
 
   . = ALIGN(8);
-  _end = .;     /* for cmsis_gcc.h  */
+  _end = .;
 }

step-5-cmsis/main.c

@@ -8,12 +8,17 @@ void SysTick_Handler(void) {
   s_ticks++;
 }
 
+uint32_t SystemCoreClock = FREQ;
+void SystemInit(void) {
+  RCC->APB2ENR |= RCC_APB2ENR_SYSCFGEN;    // Enable SYSCFG
+  SysTick_Config(SystemCoreClock / 1000);  // Tick every 1 ms
+}
+
 int main(void) {
-  uint16_t led = PIN('B', 7);            // Blue LED
-  systick_init(FREQ / 1000);             // Tick every 1 ms
-  gpio_set_mode(led, GPIO_MODE_OUTPUT);  // Set blue LED to output mode
-  uart_init(UART3, 115200);              // Initialise UART
-  uint32_t timer = 0, period = 500;      // Declare timer and 500ms period
+  uint16_t led = PIN('B', 7);                 // Blue LED
+  gpio_set_mode(led, GPIO_MODE_OUTPUT);       // Set blue LED to output mode
+  uart_init(UART_DEBUG, 115200);              // Initialise UART
+  volatile uint32_t timer = 0, period = 500;  // Declare timers
   for (;;) {
     if (timer_expired(&timer, period, s_ticks)) {
       static bool on;       // This block is executed

step-5-cmsis/mcu.h

@@ -21,14 +21,6 @@ static inline void spin(volatile uint32_t count) {
   while (count--) asm("nop");
 }
 
-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
-}
-
 #define GPIO(bank) ((GPIO_TypeDef *) (GPIOA_BASE + 0x400U * (bank)))
 enum { GPIO_MODE_INPUT, GPIO_MODE_OUTPUT, GPIO_MODE_AF, GPIO_MODE_ANALOG };
 
@@ -56,6 +48,10 @@ static inline void gpio_write(uint16_t pin, bool val) {
 #define UART2 USART2
 #define UART3 USART3
 
+#ifndef UART_DEBUG
+#define UART_DEBUG USART3
+#endif
+
 static inline void uart_init(USART_TypeDef *uart, unsigned long baud) {
   // https://www.st.com/resource/en/datasheet/stm32f429zi.pdf
   uint8_t af = 7;           // Alternate function
@@ -95,7 +91,8 @@ static inline uint8_t uart_read_byte(USART_TypeDef *uart) {
   return (uint8_t) (uart->DR & 255);
 }
 
-static inline bool timer_expired(uint32_t *t, uint32_t prd, uint32_t now) {
+static inline bool timer_expired(volatile uint32_t *t, uint32_t prd,
+                                 uint32_t now) {
   if (now + prd < *t) *t = 0;                    // Time wrapped? Reset timer
   if (*t == 0) *t = now + prd;                   // Firt poll? Set expiration
   if (*t > now) return false;                    // Not expired yet, return

step-5-cmsis/syscalls.c

@@ -56,7 +56,7 @@ int _getpid(void) {
 
 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);
+  if (fd == 1) uart_write_buf(UART_DEBUG, ptr, (size_t) len);
   return -1;
 }
 
@@ -84,3 +84,6 @@ int mkdir(const char *path, mode_t mode) {
   (void) path, (void) mode;
   return -1;
 }
+
+void _init(void) {
+}