diff --git a/stm/Makefile b/stm/Makefile
index b3483e089d..c0ae6a89c0 100644
--- a/stm/Makefile
+++ b/stm/Makefile
@@ -40,6 +40,7 @@ SRC_C = \
 	string0.c \
 	malloc0.c \
 	systick.c  \
+	gccollect.c \
 	lexerfatfs.c \
 	led.c \
 	lcd.c \
diff --git a/stm/gccollect.c b/stm/gccollect.c
new file mode 100644
index 0000000000..c0f67ac0d5
--- /dev/null
+++ b/stm/gccollect.c
@@ -0,0 +1,39 @@
+#include <stdio.h>
+
+#include "misc.h"
+#include "mpconfig.h"
+#include "qstr.h"
+#include "obj.h"
+#include "gc.h"
+#include "gccollect.h"
+#include "systick.h"
+
+void gc_helper_get_regs_and_clean_stack(machine_uint_t *regs, machine_uint_t heap_end);
+
+void gc_collect(void) {
+    uint32_t start = sys_tick_counter;
+    gc_collect_start();
+    gc_collect_root((void**)&_ram_start, ((uint32_t)&_heap_start - (uint32_t)&_ram_start) / 4);
+    machine_uint_t regs[10];
+    gc_helper_get_regs_and_clean_stack(regs, HEAP_END);
+    gc_collect_root((void**)HEAP_END, (RAM_END - HEAP_END) / 4); // will trace regs since they now live in this function on the stack
+    gc_collect_end();
+    uint32_t ticks = sys_tick_counter - start; // TODO implement a function that does this properly
+
+    if (0) {
+        // print GC info
+        gc_info_t info;
+        gc_info(&info);
+        printf("GC@%lu %lums\n", start, ticks);
+        printf(" %lu total\n", info.total);
+        printf(" %lu : %lu\n", info.used, info.free);
+        printf(" 1=%lu 2=%lu m=%lu\n", info.num_1block, info.num_2block, info.max_block);
+    }
+}
+
+static mp_obj_t pyb_gc(void) {
+    gc_collect();
+    return mp_const_none;
+}
+
+MP_DEFINE_CONST_FUN_OBJ_0(pyb_gc_obj, pyb_gc);
diff --git a/stm/gccollect.h b/stm/gccollect.h
new file mode 100644
index 0000000000..6467ec7d21
--- /dev/null
+++ b/stm/gccollect.h
@@ -0,0 +1,9 @@
+#define HEAP_END  (0x2001c000) // tunable
+#define RAM_END   (0x20020000) // fixed for chip
+
+extern uint32_t _ram_start;
+extern uint32_t _heap_start;
+
+void gc_collect(void);
+
+MP_DECLARE_CONST_FUN_OBJ(pyb_gc_obj);
diff --git a/stm/main.c b/stm/main.c
index 2ce2b6dc61..4114ec1979 100644
--- a/stm/main.c
+++ b/stm/main.c
@@ -28,6 +28,7 @@
 #include "runtime.h"
 #include "repl.h"
 #include "gc.h"
+#include "gccollect.h"
 #include "systick.h"
 #include "led.h"
 #include "servo.h"
@@ -47,8 +48,6 @@
 
 int errno;
 
-extern uint32_t _heap_start;
-
 static FATFS fatfs0;
 
 void flash_error(int n) {
@@ -180,6 +179,7 @@ static mp_obj_t pyb_info(void) {
         printf("_ebss=%p\n", &_ebss);
         printf("_estack=%p\n", &_estack);
         printf("_etext=%p\n", &_etext);
+        printf("_ram_start=%p\n", &_ram_start);
         printf("_heap_start=%p\n", &_heap_start);
     }
 
@@ -455,38 +455,6 @@ bool do_file(const char *filename) {
     }
 }
 
-#define RAM_START (0x20000000) // fixed for chip
-#define HEAP_END  (0x2001c000) // tunable
-#define RAM_END   (0x20020000) // fixed for chip
-
-void gc_helper_get_regs_and_clean_stack(machine_uint_t *regs, machine_uint_t heap_end);
-
-void gc_collect(void) {
-    uint32_t start = sys_tick_counter;
-    gc_collect_start();
-    gc_collect_root((void**)RAM_START, (((uint32_t)&_heap_start) - RAM_START) / 4);
-    machine_uint_t regs[10];
-    gc_helper_get_regs_and_clean_stack(regs, HEAP_END);
-    gc_collect_root((void**)HEAP_END, (RAM_END - HEAP_END) / 4); // will trace regs since they now live in this function on the stack
-    gc_collect_end();
-    uint32_t ticks = sys_tick_counter - start; // TODO implement a function that does this properly
-
-    if (0) {
-        // print GC info
-        gc_info_t info;
-        gc_info(&info);
-        printf("GC@%lu %lums\n", start, ticks);
-        printf(" %lu total\n", info.total);
-        printf(" %lu : %lu\n", info.used, info.free);
-        printf(" 1=%lu 2=%lu m=%lu\n", info.num_1block, info.num_2block, info.max_block);
-    }
-}
-
-mp_obj_t pyb_gc(void) {
-    gc_collect();
-    return mp_const_none;
-}
-
 mp_obj_t pyb_gpio(uint n_args, mp_obj_t *args) {
     //assert(1 <= n_args && n_args <= 2);
 
@@ -655,7 +623,7 @@ soft_reset:
         rt_store_attr(m, MP_QSTR_source_dir, rt_make_function_n(1, pyb_source_dir));
         rt_store_attr(m, MP_QSTR_main, rt_make_function_n(1, pyb_main));
         rt_store_attr(m, MP_QSTR_sync, rt_make_function_n(0, pyb_sync));
-        rt_store_attr(m, MP_QSTR_gc, rt_make_function_n(0, pyb_gc));
+        rt_store_attr(m, MP_QSTR_gc, (mp_obj_t)&pyb_gc_obj);
         rt_store_attr(m, MP_QSTR_delay, rt_make_function_n(1, pyb_delay));
 #if MICROPY_HW_HAS_SWITCH
         rt_store_attr(m, MP_QSTR_switch, (mp_obj_t)&pyb_switch_obj);
diff --git a/stm/stm32f405.ld b/stm/stm32f405.ld
index c19e6a1c19..fbfc584f9d 100644
--- a/stm/stm32f405.ld
+++ b/stm/stm32f405.ld
@@ -69,6 +69,7 @@ SECTIONS
     {
         . = ALIGN(4);
         _sdata = .;        /* 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 */