diff --git a/stm/file.c b/stm/file.c
index 35bfca16a515134a807a6bd1029f7d111b35e121..84f7251fec127da91549af51630cb436a249f40d 100644
--- a/stm/file.c
+++ b/stm/file.c
@@ -3,7 +3,6 @@
 
 #include "misc.h"
 #include "mpconfig.h"
-#include "mpconfigport.h"
 #include "qstr.h"
 #include "obj.h"
 #include "file.h"
diff --git a/stm/gccollect.c b/stm/gccollect.c
index c0f67ac0d54c7397e95dea8fffb064e6fd346dd1..cea0bc56eb4aace68623940d86ccf9c8a8922c21 100644
--- a/stm/gccollect.c
+++ b/stm/gccollect.c
@@ -13,10 +13,10 @@ void gc_helper_get_regs_and_clean_stack(machine_uint_t *regs, machine_uint_t hea
 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);
+    gc_collect_root((void**)&_ram_start, (&_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_helper_get_regs_and_clean_stack(regs, (machine_uint_t)&_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
 
diff --git a/stm/gccollect.h b/stm/gccollect.h
index 6467ec7d21daeb3de7b988ef4443299b3445f001..9187f0e9df1c20ea9c93e8fdb3a39c67f446b8bb 100644
--- a/stm/gccollect.h
+++ b/stm/gccollect.h
@@ -1,8 +1,7 @@
-#define HEAP_END  (0x2001c000) // tunable
-#define RAM_END   (0x20020000) // fixed for chip
-
 extern uint32_t _ram_start;
 extern uint32_t _heap_start;
+extern uint32_t _ram_end;
+extern uint32_t _heap_end;
 
 void gc_collect(void);
 
diff --git a/stm/main.c b/stm/main.c
index 9fc9633ff2dcd9a290e2c7d52fe372b263a3e988..9f2b6d564aaaed4ecbdf195e5badb3f8cc058b74 100644
--- a/stm/main.c
+++ b/stm/main.c
@@ -206,12 +206,14 @@ static mp_obj_t pyb_info(void) {
     return mp_const_none;
 }
 
+#if MICROPY_HW_HAS_SDCARD
 // SD card test
 static mp_obj_t pyb_sd_test(void) {
     extern void sdio_init(void);
     sdio_init();
     return mp_const_none;
 }
+#endif
 
 static void SYSCLKConfig_STOP(void) {
     /* After wake-up from STOP reconfigure the system clock */
@@ -594,7 +596,7 @@ int main(void) {
 soft_reset:
 
     // GC init
-    gc_init(&_heap_start, (void*)HEAP_END);
+    gc_init(&_heap_start, &_heap_end);
 
     // Micro Python init
     qstr_init();
diff --git a/stm/stm32f405.ld b/stm/stm32f405.ld
index fbfc584f9d4cf2e129d7509d70214118b104b654..5cef201a9a8eb6fbd0eacc4d720ef682112e787a 100644
--- a/stm/stm32f405.ld
+++ b/stm/stm32f405.ld
@@ -19,6 +19,9 @@ _minimum_heap_size = 16K;
 /* top end of the stack */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
 
+_ram_end = 0x20020000;
+_heap_end = 0x2001c000;
+
 /* define output sections */
 SECTIONS
 {