stm: Tidy up memory labels; optimise GC root scanning.

Addresses issues #272 and #273.

stm/gccollect.c

@@ -8,20 +8,36 @@
 #include "gccollect.h"
 #include "systick.h"
 
-void gc_helper_get_regs_and_clean_stack(machine_uint_t *regs, machine_uint_t heap_end);
+machine_uint_t gc_helper_get_regs_and_sp(machine_uint_t *regs);
+
+// obsolete
+// void gc_helper_get_regs_and_clean_stack(machine_uint_t *regs, machine_uint_t heap_end);
 
 void gc_collect(void) {
+    // get current time, in case we want to time the GC
     uint32_t start = sys_tick_counter;
+
+    // start the GC
     gc_collect_start();
-    gc_collect_root((void**)&_ram_start, ((uint32_t)&_heap_start - (uint32_t)&_ram_start) / sizeof(uint32_t));
+
+    // scan everything in RAM before the heap
+    // this includes the data and bss segments
+    // TODO possibly don't need to scan data, since all pointers should start out NULL and be in bss
+    gc_collect_root((void**)&_ram_start, ((uint32_t)&_bss_end - (uint32_t)&_ram_start) / sizeof(uint32_t));
+
+    // get the registers and the sp
     machine_uint_t regs[10];
-    gc_helper_get_regs_and_clean_stack(regs, (machine_uint_t)&_heap_end);
-    gc_collect_root((void**)&_heap_end, ((uint32_t)&_ram_end - (uint32_t)&_heap_end) / sizeof(uint32_t)); // will trace regs since they now live in this function on the stack
+    machine_uint_t sp = gc_helper_get_regs_and_sp(regs);
+
+    // trace the stack, including the registers (since they live on the stack in this function)
+    gc_collect_root((void**)sp, ((uint32_t)&_ram_end - sp) / sizeof(uint32_t));
+
+    // end the GC
     gc_collect_end();
-    uint32_t ticks = sys_tick_counter - start; // TODO implement a function that does this properly
 
     if (0) {
         // print GC info
+        uint32_t ticks = sys_tick_counter - start; // TODO implement a function that does this properly
         gc_info_t info;
         gc_info(&info);
         printf("GC@%lu %lums\n", start, ticks);

stm/gccollect.h

+// variables defining memory layout
+// (these probably belong somewhere else...)
+extern uint32_t _text_end;
+extern uint32_t _data_start_init;
 extern uint32_t _ram_start;
+extern uint32_t _data_start;
+extern uint32_t _data_end;
+extern uint32_t _bss_start;
+extern uint32_t _bss_end;
 extern uint32_t _heap_start;
-extern uint32_t _ram_end;
 extern uint32_t _heap_end;
+extern uint32_t _stack_end;
+extern uint32_t _ram_end;
 
 void gc_collect(void);
 

stm/gchelper.s

@@ -4,6 +4,32 @@
     .text
     .align  2
 
+@ uint gc_helper_get_regs_and_sp(r0=uint regs[10])
+    .global gc_helper_get_regs_and_sp
+    .thumb
+    .thumb_func
+    .type   gc_helper_get_regs_and_sp, %function
+gc_helper_get_regs_and_sp:
+    @ store registers into given array
+    str     r4, [r0], #4
+    str     r5, [r0], #4
+    str     r6, [r0], #4
+    str     r7, [r0], #4
+    str     r8, [r0], #4
+    str     r9, [r0], #4
+    str     r10, [r0], #4
+    str     r11, [r0], #4
+    str     r12, [r0], #4
+    str     r13, [r0], #4
+
+    @ return the sp
+    mov     r0, sp
+    bx      lr
+
+
+@ this next function is now obsolete
+
+    .size   gc_helper_get_regs_and_clean_stack, .-gc_helper_get_regs_and_clean_stack
 @ void gc_helper_get_regs_and_clean_stack(r0=uint regs[10], r1=heap_end)
     .global gc_helper_get_regs_and_clean_stack
     .thumb

stm/main.c

@@ -171,20 +171,13 @@ static mp_obj_t pyb_info(void) {
 
     // to print info about memory
     {
-        extern void *_sidata;
-        extern void *_sdata;
-        extern void *_edata;
-        extern void *_sbss;
-        extern void *_ebss;
-        extern void *_estack;
-        extern void *_etext;
-        printf("_etext=%p\n", &_etext);
-        printf("_sidata=%p\n", &_sidata);
-        printf("_sdata=%p\n", &_sdata);
-        printf("_edata=%p\n", &_edata);
-        printf("_sbss=%p\n", &_sbss);
-        printf("_ebss=%p\n", &_ebss);
-        printf("_estack=%p\n", &_estack);
+        printf("_text_end=%p\n", &_text_end);
+        printf("_data_start_init=%p\n", &_data_start_init);
+        printf("_data_start=%p\n", &_data_start);
+        printf("_data_end=%p\n", &_data_end);
+        printf("_bss_start=%p\n", &_bss_start);
+        printf("_bss_end=%p\n", &_bss_end);
+        printf("_stack_end=%p\n", &_stack_end);
         printf("_ram_start=%p\n", &_ram_start);
         printf("_heap_start=%p\n", &_heap_start);
         printf("_heap_end=%p\n", &_heap_end);

stm/startup_stm32f40xx.s

@@ -47,15 +47,15 @@
 
 /* start address for the initialization values of the .data section. 
 defined in linker script */
-.word  _sidata
+.word  _data_start_init
 /* start address for the .data section. defined in linker script */  
-.word  _sdata
+.word  _data_start
 /* end address for the .data section. defined in linker script */
-.word  _edata
+.word  _data_end
 /* start address for the .bss section. defined in linker script */
-.word  _sbss
+.word  _bss_start
 /* end address for the .bss section. defined in linker script */
-.word  _ebss
+.word  _bss_end
 /* stack used for SystemInit_ExtMemCtl; always internal RAM used */
 
 /**
@@ -90,9 +90,9 @@ LoopCopyDataInit:
   cmp  r2, r3
   bcc  CopyDataInit
   */
-    ldr     r0, =_sidata        @ source pointer
-    ldr     r1, =_sdata         @ destination pointer
-    ldr     r2, =_edata         @ maximum destination pointer
+    ldr     r0, =_data_start_init   @ source pointer
+    ldr     r1, =_data_start        @ destination pointer
+    ldr     r2, =_data_end          @ maximum destination pointer
     b       data_init_entry
 data_init_loop:
     ldr     r3, [r0], #4
@@ -117,8 +117,8 @@ LoopFillZerobss:
   */
 
     movs    r0, #0              @ source value
-    ldr     r1, =_sbss          @ destination pointer
-    ldr     r2, =_ebss          @ maximum destination pointer
+    ldr     r1, =_bss_start     @ destination pointer
+    ldr     r2, =_bss_end       @ maximum destination pointer
     b       bss_init_entry
 bss_init_loop:
     str     r0, [r1], #4
@@ -158,7 +158,7 @@ Infinite_Loop:
     
     
 g_pfnVectors:
-  .word  _estack
+  .word  _stack_end
   .word  Reset_Handler
   .word  NMI_Handler
   .word  HardFault_Handler

stm/stm32f405.ld

@@ -17,7 +17,7 @@ _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
  
 /* top end of the stack */
-_estack = ORIGIN(RAM) + LENGTH(RAM);
+_stack_end = ORIGIN(RAM) + LENGTH(RAM);
 
 /* RAM extents for the garbage collector */
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
@@ -47,8 +47,8 @@ SECTIONS
     /*  *(.glue_7t)  */    /* glue thumb to arm code */
 
         . = ALIGN(4);
-        _etext = .;        /* define a global symbol at end of code */
-        _sidata = _etext;  /* This is used by the startup in order to initialize the .data secion */
+        _text_end = .;     /* define a global symbol at end of code */
+        _data_start_init = _text_end; /* This is used by the startup in order to initialize the .data secion */
     } >FLASH_TEXT
      
     /*
@@ -69,29 +69,29 @@ SECTIONS
     The program executes knowing that the data is in the RAM
     but the loader puts the initial values in the FLASH (inidata).
     It is one task of the startup to copy the initial values from FLASH to RAM. */
-    .data : AT ( _sidata )
+    .data : AT ( _data_start_init )
     {
         . = ALIGN(4);
-        _sdata = .;        /* create a global symbol at data start; used by startup code in order to initialise the .data section in RAM */
+        _data_start = .;   /* create a global symbol at data start; used by startup code in order to initialise the .data section in RAM */
         _ram_start = .;    /* create a global symbol at ram start for garbage collector */
         *(.data)           /* .data sections */
         *(.data*)          /* .data* sections */
 
         . = ALIGN(4);
-        _edata = .;        /* define a global symbol at data end; used by startup code in order to initialise the .data section in RAM */
+        _data_end = .;     /* define a global symbol at data end; used by startup code in order to initialise the .data section in RAM */
     } >RAM
             
     /* Uninitialized data section */
     .bss :
     {
         . = ALIGN(4);
-        _sbss = .;         /* define a global symbol at bss start; used by startup code */
+        _bss_start = .;    /* define a global symbol at bss start; used by startup code */
         *(.bss)
         *(.bss*)
         *(COMMON)
 
         . = ALIGN(4);
-        _ebss = .;         /* define a global symbol at bss end; used by startup code */
+        _bss_end = .;      /* define a global symbol at bss end; used by startup code and GC */
     } >RAM
 
     /* this is to define the start of the heap, and make sure we have a minimum size */