mirror of
https://github.com/rfivet/stm32bringup.git
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266 lines
7.4 KiB
HTML
266 lines
7.4 KiB
HTML
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<title>1.8 Three-stage Rocket</title>
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<link type="text/css" rel="stylesheet" href="style.css">
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</head>
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<body>
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<h1>1.8 Three-stage Rocket</h1>
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As I merge the cstartup with the ledtick code, I split the
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functionalities between three files according to the three phases: boot,
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initialization and main execution.
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<ul>
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<li> <b>startup.c</b> is mainly concerned with the early set up of the board:
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initializing the memory, calling system initialization and then
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executing the main C function if initialization is successful.
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</ul><ul>
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<li> <b>init.c</b> holds the middleware implementation and will abstract the
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peripherals into higher level interfaces. Its entry point is the
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<code>init()</code> function.
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</ul><ul>
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<li> the <code>main()</code> C function will be the focus of the last file and
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it should be written in a subset of standard C. As an example I will use
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<b>success.c</b>.
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</ul>
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<pre>
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/* success.c -- success does nothing, successfully */
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#include <stdlib.h>
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int main( void) {
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return EXIT_SUCCESS ;
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}
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</pre>
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<h2>startup.c</h2>
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Beside the interrupt vector and the <code>Reset_Handler()</code> that calls
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<code>init()</code> and <code>main()</code>, I have created stubs for all the
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System Exceptions listed in the Programming Manual. For those, if there is no
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implementation avalable in <b>init.c</b>, the linker will use the
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<code>Default_Handler()</code> provided with the <code>__attribute__()</code>
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Gnu C extension.
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<pre>
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/* Memory locations defined by linker script */
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extern long __StackTop ; /* &__StackTop points after end of stack */
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void Reset_Handler( void) ; /* Entry point for execution */
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extern const long __etext[] ; /* start of initialized data copy in flash */
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extern long __data_start__[] ;
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extern long __bss_start__[] ;
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extern long __bss_end__ ; /* &__bss_end__ points after end of bss */
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/* Stubs for System Exception Handler */
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void Default_Handler( void) ;
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#define dflt_hndlr( fun) void fun##_Handler( void) \
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__attribute__((weak,alias("Default_Handler")))
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dflt_hndlr( NMI) ;
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dflt_hndlr( HardFault) ;
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dflt_hndlr( SVCall) ;
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dflt_hndlr( PendSV) ;
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dflt_hndlr( SysTick) ;
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/* Interrupt vector table:
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* 1 Stack Pointer reset value
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* 15 System Exceptions
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* NN Device specific Interrupts
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*/
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typedef void (*isr_p)( void) ;
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isr_p const isr_vector[ 16] __attribute__((section(".isr_vector"))) = {
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(isr_p) &__StackTop,
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/* System Exceptions */
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Reset_Handler,
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NMI_Handler,
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HardFault_Handler,
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0, 0, 0, 0, 0, 0, 0,
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SVCall_Handler,
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0, 0,
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PendSV_Handler,
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SysTick_Handler
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} ;
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extern int init( void) ;
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extern int main( void) ;
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void Reset_Handler( void) {
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const long *f ; /* from, source constant data from FLASH */
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long *t ; /* to, destination in RAM */
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/* Assume:
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** __bss_start__ == __data_end__
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** All sections are 4 bytes aligned
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*/
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f = __etext ;
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for( t = __data_start__ ; t < __bss_start__ ; t += 1)
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*t = *f++ ;
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while( t < &__bss_end__)
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*t++ = 0 ;
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if( init() == 0)
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main() ;
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for( ;;)
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__asm( "WFI") ; /* Wait for interrupt */
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}
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void Default_Handler( void) {
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for( ;;) ;
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}
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</pre>
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Except for the future addition of stubs to handle the device specific
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interrupts, this file will not grow much anymore.
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<h2>init.c</h2>
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This is the embryo of an hardware abstraction layer where most of the
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device specific code will be added. The current code is the peripherals
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part of <b>ledtick.c</b>.
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<pre>
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#define SYSTICK ((volatile long *) 0xE000E010)
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#define SYSTICK_CSR SYSTICK[ 0]
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#define SYSTICK_RVR SYSTICK[ 1]
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#define SYSTICK_CVR SYSTICK[ 2]
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#define RCC ((volatile long *) 0x40021000)
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#define RCC_AHBENR RCC[ 5]
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#define RCC_AHBENR_IOPBEN 0x00040000 /* 18: I/O port B clock enable */
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#define GPIOB ((volatile long *) 0x48000400)
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#define GPIOB_MODER GPIOB[ 0]
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#define GPIOB_ODR GPIOB[ 5]
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int init( void) {
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/* By default SYSCLK == HSI [8MHZ] */
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/* SYSTICK */
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SYSTICK_RVR = 1000000 - 1 ; /* HBA / 8 */
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SYSTICK_CVR = 0 ;
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SYSTICK_CSR = 3 ; /* HBA / 8, Interrupt ON, Enable */
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/* SysTick_Handler will execute every 1s from now on */
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/* User LED ON */
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RCC_AHBENR |= RCC_AHBENR_IOPBEN ; /* Enable IOPB periph */
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GPIOB_MODER |= 1 << (1 * 2) ; /* PB1 Output [01], over default 00 */
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/* OTYPER Push-Pull by default */
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/* PB1 output default LOW at reset */
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return 0 ;
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}
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void SysTick_Handler( void) {
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GPIOB_ODR ^= 1 << 1 ; /* Toggle PB1 (User LED) */
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}
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</pre>
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<h2>Makefile</h2>
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As I now build from multiple source files, I have modified the
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<b>Makefile</b> to list the sources that combine together. All steps I have
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done so far can be found in the commented <code>SRCS</code> lines. Single file
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steps can be build explicitly (<code>make ledon.hex</code>) or implicitly
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(<code>make</code>) after removing the comment on the corresponding
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<code>SRCS</code> line. Multiple file steps can only be build implicitly when
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their <code>SRCS</code> line is uncommented.
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<pre>
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### Build environment selection
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ifeq (linux, $(findstring linux, $(MAKE_HOST)))
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GCCDIR = $(HOME)/Packages/arm-gnu-toolchain-13.3.rel1-x86_64-arm-none-eabi
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else
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GCCDIR = "D:/Program Files (x86)/GNU Arm Embedded Toolchain/arm-gnu-toolchain-13.3.rel1-mingw-w64-i686-arm-none-eabi"
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endif
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BINPFX = @$(GCCDIR)/bin/arm-none-eabi-
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CC = $(BINPFX)gcc
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LD = $(BINPFX)ld
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OBJCOPY = $(BINPFX)objcopy
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OBJDUMP = $(BINPFX)objdump
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SIZE = $(BINPFX)size
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### STM32F030F4P6 based board
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PROJECT = f030f4
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#SRCS = boot.c
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#SRCS = ledon.c
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#SRCS = blink.c
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#SRCS = ledtick.c
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#SRCS = cstartup.c
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SRCS = startup.c init.c success.c
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OBJS = $(SRCS:.c=.o)
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CPU = -mthumb -mcpu=cortex-m0
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CFLAGS = $(CPU) -g -Wall -Wextra -Os
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LD_SCRIPT = $(PROJECT).ld
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### Build rules
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.PHONY: clean all
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all: $(PROJECT).hex $(PROJECT).bin
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clean:
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@echo CLEAN
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@rm -f *.o *.elf *.map *.lst *.bin *.hex
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$(PROJECT).elf: $(OBJS)
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@echo $@
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$(LD) -T$(LD_SCRIPT) -Map=$(PROJECT).map -cref -o $@ $(OBJS)
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$(SIZE) $@
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$(OBJDUMP) -hS $@ > $(PROJECT).lst
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%.elf: %.o
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@echo $@
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$(LD) -T$(LD_SCRIPT) -Map=$*.map -cref -o $@ $<
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$(SIZE) $@
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$(OBJDUMP) -hS $@ > $*.lst
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%.bin: %.elf
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@echo $@
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$(OBJCOPY) -O binary $< $@
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%.hex: %.elf
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@echo $@
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$(OBJCOPY) -O ihex $< $@
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</pre>
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A successful build will generate the files <b>f030f4.hex</b>, <b>f030f4.bin</b>,
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<b>f030f4.map</b>, <b>f030f4.lst</b>.
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<h2>Build and Test</h2>
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Even if <b>stdlib.h</b> is included in <b>success.c</b>, there is no C
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libraries needed to complete the build as only the constant
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<code>EXIT_SUCCESS</code> from that header is used. Furthermore, default
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location of the header files is derived by the compiler from the location of
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gcc.
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<pre>
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$ make
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f030f4.elf
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text data bss dec hex filename
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216 0 0 216 d8 f030f4.elf
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f030f4.hex
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f030f4.bin
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</pre>
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Building shows an increase in code, still no data.
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<p>
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Once <b>f030f4.hex</b> is loaded into the board, the behavior is the same
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as <b>ledtick.hex</b>. The new file structure and data initialization
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didn’t introduce any <del>bugs</del> changes, just code overhead.
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<h2>Checkpoint</h2>
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This step was mainly to achieve a better structure for future evolution.
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<p>
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<a href="19_publish.html">Next</a>, I will make the code available in a
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public git repository.
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<hr>© 2020-2024 Renaud Fivet
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</body>
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</html>
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