finish bootloader and memory layout

boot.s

@@ -1,46 +1,67 @@
 /* Simple startup file for Cortex-M3 */
 
- /* Thumb-2 instructions are only supported in unified syntax mode */
- .syntax unified
+/* Thumb-2 instructions are only supported in unified syntax mode */
+.syntax unified
 
 /* Vector table definition */
- .section ".cs3.interrupt_vector"
- .long  __cs3_stack                 /* Top of Stack                 */
- .long  Reset_Handler               /* Reset Handler                */
- .long  NMI_Handler                 /* NMI Handler                  */
- .long  HardFault_Handler           /* Hard Fault Handler           */
- .long  MemManage_Handler           /* MPU Fault Handler            */
- .long  BusFault_Handler            /* Bus Fault Handler            */
- .long  UsageFault_Handler          /* Usage Fault Handler          */
- .long  0                           /* Reserved                     */
- .long  0                           /* Reserved                     */
- .long  0                           /* Reserved                     */
- .long  0                           /* Reserved                     */
- .long  SVC_Handler                 /* SVCall Handler               */
- .long  DebugMon_Handler            /* Debug Monitor Handler        */
- .long  0                           /* Reserved                     */
- .long  PendSV_Handler              /* PendSV Handler               */
- .long  SysTick_Handler             /* SysTick Handler              */
+.section ".isr_vector", "a"
+.long  _sram_end                   /* Top of Stack                 */
+.long  Reset_Handler               /* Reset Handler                */
+.long  NMI_Handler                 /* NMI Handler                  */
+.long  HardFault_Handler           /* Hard Fault Handler           */
+.long  MemManage_Handler           /* MPU Fault Handler            */
+.long  BusFault_Handler            /* Bus Fault Handler            */
+.long  UsageFault_Handler          /* Usage Fault Handler          */
+.long  0                           /* Reserved                     */
+.long  0                           /* Reserved                     */
+.long  0                           /* Reserved                     */
+.long  0                           /* Reserved                     */
+.long  SVC_Handler                 /* SVCall Handler               */
+.long  DebugMon_Handler            /* Debug Monitor Handler        */
+.long  0                           /* Reserved                     */
+.long  PendSV_Handler              /* PendSV Handler               */
+.long  SysTick_Handler             /* SysTick Handler              */
 
- /* Program section */
- .section ".text"
+/* Program section */
+.section ".text"
 
- /* Declare as thumb function. Otherwise it will not be linked
- * correctly
- */
- .thumb_func
- /* Export the symbol so linker can see this */
- .global Reset_Handler
+/* Declare as thumb function. Otherwise it will not be linked
+* correctly
+*/
+.thumb_func
+/* Export the symbol so linker can see this */
+.global Reset_Handler
 Reset_Handler:
- /* Jump to main(), a thumb function */
- LDR     R0, =main
- BX      R0
- /* If main() ever exit, this should hold MCU from running wild */
- B       .
+CopyDataInitializersStart:
+  ldr   r0, =_sdata   /* write to this addr */
+  ldr   r1, =_edata   /* until you get to this addr */
+  ldr   r2, =_sidata  /* reading from this addr */
+  b     CopyDataInitializersEnterLoop
+CopyDataInitializersLoop:
+  ldmia r2!, {r3}
+  stmia r0!, {r3}
+CopyDataInitializersEnterLoop:
+  cmp   r0, r1
+  bcc   CopyDataInitializersLoop
+WriteZeroToBssStart:
+  ldr r0, =_sbss
+  ldr r1, =_ebss
+  movs r2, #0
+  b WriteZeroToBssEnterLoop
+WriteZeroToBssLoop:
+  stmia r0!, {r2}
+WriteZeroToBssEnterLoop:
+  cmp r0, r1
+  bcc WriteZeroToBssLoop
+/* Jump to main(), a thumb function */
+  LDR     R0, =setup
+  BLX     R0
+  LDR     R0, =main
+  BLX     R0
+/* If main() ever exit, this should hold MCU from running wild */
+  B       .
 
-/* This is how the lazy guy doing it: by aliasing all the
- * interrupts into single address
- */
+/* All standard interrupts will land here */
 .thumb_func
 NMI_Handler:
 .thumb_func

linker.ld

@@ -1,23 +1,61 @@
+ENTRY(Reset_Handler)
+
 /* memory layout for an STM32L476RG */
 MEMORY
 {
   FLASH (rx)  : ORIGIN = 0x08000000, LENGTH = 0x100000
   SRAM (xrw)  : ORIGIN = 0x20000000, LENGTH = 0x18000
 }
+/* End of SRAM for top of stack */
+_sram_end = 0x20000000 + 0x18000;
 
-/* output sections */
+/* Sections */
 SECTIONS
 {
-  /* program code into FLASH */
+  .isr_vector :
+  {
+    . = ALIGN(4);
+    KEEP(*(.isr_vector))
+    . = ALIGN(4);
+  } >FLASH
+
   .text :
   {
-    *(.vector_table)    /* Vector table */
-    *(.text)            /* Program code */
+    . = ALIGN(4);
+    *(.text)           /* .text sections (code) */
+    *(.text*)         /* .text sections (code) */
+    *(.rodata)         /* .rodata sections (constants, strings, etc.) */
+    *(.rodata*)       /* .rodata sections (constants, strings, etc.) */
+    . = ALIGN(4);
   } >FLASH
 
-  /* uninitialized global and static variables into SRAM */
+  .rodata :
+  {
+    . = ALIGN(4);
+    *(.rodata)         /* .rodata sections (constants, strings, etc.) */
+    *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
+    . = ALIGN(4);
+  } >FLASH
+
+  _sidata = LOADADDR(.data);
   .data :
   {
-    *(.data)
+    . = ALIGN(4);
+    _sdata = .;        /* create a global symbol at data start */
+    *(.data)           /* .data sections */
+    *(.data*)          /* .data* sections */
+    . = ALIGN(4);
+    _edata = .;        /* define a global symbol at data end */
+  } >SRAM AT> FLASH
+
+  .bss :
+  {
+    . = ALIGN(4);
+    _sbss = .;
+    *(.bss)
+    *(.bss*)
+    *(COMMON)
+    . = ALIGN(4);
+    _ebss = .;
   } >SRAM
 }

main.c

@@ -1,6 +1,6 @@
 #include <stdint.h>
 
-#define MMIO32(addr)    (*(volatile uint32_t *)(addr))
+#define MMIO32(addr)        (*(volatile uint32_t *)(addr))
 #define PERIPH_BASE_AHB2    (0x48000000U)
 #define GPIO_PORT_A_BASE    (PERIPH_BASE_AHB2 + 0x0000)
 #define GPIOA               GPIO_PORT_A_BASE
@@ -13,31 +13,25 @@
 #define RCC_AHB2ENR_OFFSET  0x4c
 #define RCC_AHB2ENR         MMIO32(RCC_BASE + RCC_AHB2ENR_OFFSET)
 
-/* work out end of RAM address as initial stack pointer */
-#define SRAM_BASE       0x20000000
-#define SRAM_SIZE       0x18000 // 96KiB RAM
-#define SRAM_END        (SRAM_BASE + SRAM_SIZE)
-
 # define nop()  __asm__ __volatile__ ("nop" ::)
 
-int main(void) {
+int ontime  = 500000;
+int offtime = 250000;
+
+void setup() {
   RCC_AHB2ENR |= 1;
   nop();
   nop();
   GPIOA_MODER = 0xAB555555;
-  GPIOA_ODR = 0xFFFFFFFF;
+}
+
+int main() {
   int n;
   while (1) {
-    for(n=0;n<500000;n++) nop();
-    GPIOA_ODR = 0x0;
-    for(n=0;n<500000;n++) nop();
     GPIOA_ODR = 0xFFFF;
+    for(n=0;n<ontime;n++) nop();
+    GPIOA_ODR = 0x0;
+    for(n=0;n<offtime;n++) nop();
   }
+  return(0);
 }
-
-/* vector table */
-uint32_t vector_table[] __attribute__((section(".vector_table"))) =
-{
-  (uint32_t)SRAM_END,   // initial stack pointer
-  (uint32_t)main        // main as Reset_Handler
-};

make.sh

@@ -1,5 +1,6 @@
 set -e
 arm-none-eabi-gcc --specs=nosys.specs -std=gnu11 -Wall -pedantic -g -O2 -mlittle-endian -mthumb -mthumb-interwork -mcpu=cortex-m4 -fsingle-precision-constant -Wdouble-promotion -c main.c -o main.o
-arm-none-eabi-ld -o main.elf -T linker.ld main.o
+arm-none-eabi-gcc --specs=nosys.specs -std=gnu11 -Wall -pedantic -g -O2 -mlittle-endian -mthumb -mthumb-interwork -mcpu=cortex-m4 -fsingle-precision-constant -Wdouble-promotion -c boot.s -o boot.o
+arm-none-eabi-ld -o main.elf -T linker.ld boot.o main.o
 arm-none-eabi-objcopy -O binary main.elf main.bin
 st-flash write main.bin 0x8000000