diff --git a/Makefile.firmware b/Makefile.firmware
index 301d7d74..d3c89383 100644
--- a/Makefile.firmware
+++ b/Makefile.firmware
@@ -313,6 +313,7 @@ OBJ_MP += $(addprefix $(BUILD_MP)/,\
 # OBJ micropython/
 OBJ_FW += $(addprefix $(BUILD_FW)/, \
 	firmware/main.o \
+	firmware/mphalport.o \
 	trezorhal/flash.o \
 	trezorhal/rng.o \
 	trezorhal/sdcard.o \
diff --git a/micropython/firmware/main.c b/micropython/firmware/main.c
index c55830f6..5cf675df 100644
--- a/micropython/firmware/main.c
+++ b/micropython/firmware/main.c
@@ -20,10 +20,6 @@
 #include "usb.h"
 
 void SystemClock_Config(void);
-void USBD_CDC_TxAlways(const uint8_t * buf, uint32_t len);
-int USBD_CDC_Rx(uint8_t * buf, uint32_t len, uint32_t timeout);
-
-// Errors
 
 void NORETURN nlr_jump_fail(void *val) {
     for (;;) {}
@@ -60,6 +56,11 @@ int main(void) {
     }
     RCC->CSR |= RCC_CSR_RMVF;
 
+    // Enable CPU ticks
+    CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
+    DWT->CYCCNT = 0;
+    DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
+
     pendsv_init();
 
     if (0 != flash_init()) {
@@ -114,7 +115,7 @@ void MP_WEAK __assert_func(const char *file, int line, const char *func, const c
 }
 #endif
 
-// I/O
+// Micropython file I/O stubs
 
 mp_lexer_t *mp_lexer_new_from_file(const char *filename) {
     return NULL;
@@ -129,32 +130,6 @@ mp_obj_t mp_builtin_open(uint n_args, const mp_obj_t *args, mp_map_t *kwargs) {
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_open_obj, 1, mp_builtin_open);
 
-int mp_hal_stdin_rx_chr(void) {
-    for (;;) {
-        byte c;
-        if (USBD_CDC_Rx(&c, 1, 0) != 0) {
-            return c;
-        }
-    }
-}
-
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
-    USBD_CDC_TxAlways((const uint8_t*)str, len);
-}
-
 int mp_reader_new_file(mp_reader_t *reader, const char *filename) {
     return 2; // assume error was "file not found"
 }
-
-// Time
-
-bool mp_hal_ticks_cpu_enabled;
-
-void mp_hal_ticks_cpu_enable(void) {
-    if (!mp_hal_ticks_cpu_enabled) {
-        // CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
-        // DWT->CYCCNT = 0;
-        // DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
-        mp_hal_ticks_cpu_enabled = true;
-    }
-}
diff --git a/micropython/firmware/mpconfigport.h b/micropython/firmware/mpconfigport.h
index 4ff5cb6e..21aa0f24 100644
--- a/micropython/firmware/mpconfigport.h
+++ b/micropython/firmware/mpconfigport.h
@@ -24,12 +24,8 @@
  * THE SOFTWARE.
  */
 
-#include <limits.h>
-#include <stdint.h>
-#include <stdbool.h>
-#include <alloca.h>
-
-#define MICROPY_DEBUG_PRINTERS (1)
+#include <stdbool.h> // bool
+#include <alloca.h>  // alloca
 
 // Memory allocation policies
 #define MICROPY_ALLOC_PATH_MAX      (128)
@@ -117,21 +113,16 @@
 #include STM32_HAL_H
 
 #define BYTES_PER_WORD (4)
-#define MP_HAL_UNIQUE_ID_ADDRESS (0x1fff7a10)
+
 #define MICROPY_MAKE_POINTER_CALLABLE(p) ((void*)((mp_uint_t)(p) | 1))
-#define MP_PLAT_PRINT_STRN(str, len) mp_hal_stdout_tx_strn_cooked(str, len)
 
-// This port is intended to be 32-bit, but unfortunately, int32_t for
-// different targets may be defined in different ways - either as int
-// or as long. This requires different printf formatting specifiers
-// to print such value. So, we avoid int32_t and use int directly.
+#define INT_FMT  "%d"
 #define UINT_FMT "%u"
-#define INT_FMT "%d"
-typedef int mp_int_t; // must be pointer size
-typedef unsigned mp_uint_t; // must be pointer size
-typedef long mp_off_t;
+#define MP_SSIZE_MAX (0x0fffffff)
 
-#define MP_SSIZE_MAX INT_MAX
+typedef long mp_off_t;
+typedef int mp_int_t;
+typedef unsigned mp_uint_t;
 
 static inline void enable_irq(mp_uint_t state) {
     __set_PRIMASK(state);
@@ -147,15 +138,15 @@ static inline mp_uint_t disable_irq(void) {
 #define MICROPY_END_ATOMIC_SECTION(state)  enable_irq(state)
 #define MICROPY_EVENT_POLL_HOOK            __WFI();
 
-#define MICROPY_MIN_USE_CORTEX_CPU  (1)
-#define MICROPY_MIN_USE_STM32_MCU   (1)
 #define MICROPY_HW_BOARD_NAME "TREZORv2"
 #define MICROPY_HW_MCU_NAME "STM32F405VG"
 #define MICROPY_PY_SYS_PLATFORM "trezor"
 
-#define MP_STATE_PORT MP_STATE_VM
 #define MICROPY_PORT_ROOT_POINTERS
 
+#define MP_STATE_PORT MP_STATE_VM
+
+// Extra built in modules to add to the list of known ones
 extern const struct _mp_obj_module_t mp_module_utime;
 extern const struct _mp_obj_module_t mp_module_TrezorConfig;
 extern const struct _mp_obj_module_t mp_module_TrezorCrypto;
@@ -163,8 +154,6 @@ extern const struct _mp_obj_module_t mp_module_TrezorDebug;
 extern const struct _mp_obj_module_t mp_module_TrezorMsg;
 extern const struct _mp_obj_module_t mp_module_TrezorUi;
 extern const struct _mp_obj_module_t mp_module_TrezorUtils;
-
-// Extra built in modules to add to the list of known ones
 #define MICROPY_PORT_BUILTIN_MODULES \
     { MP_OBJ_NEW_QSTR(MP_QSTR_utime), (mp_obj_t)&mp_module_utime }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_TrezorConfig), (mp_obj_t)&mp_module_TrezorConfig }, \
@@ -178,17 +167,7 @@ extern const struct _mp_obj_module_t mp_module_TrezorUtils;
 #define MICROPY_PORT_BUILTINS \
     { MP_OBJ_NEW_QSTR(MP_QSTR_open), (mp_obj_t)&mp_builtin_open_obj },
 
+// Make sure all allocations are done through GC
 #define malloc(n) m_malloc(n)
 #define free(p) m_free(p)
 #define realloc(p, n) m_realloc(p, n)
-
-extern bool mp_hal_ticks_cpu_enabled;
-
-void mp_hal_ticks_cpu_enable(void);
-
-static inline mp_uint_t mp_hal_ticks_cpu(void) {
-    if (!mp_hal_ticks_cpu_enabled) {
-        mp_hal_ticks_cpu_enable();
-    }
-    return DWT->CYCCNT;
-}
diff --git a/micropython/firmware/mphalport.c b/micropython/firmware/mphalport.c
new file mode 100644
index 00000000..8cc1f850
--- /dev/null
+++ b/micropython/firmware/mphalport.c
@@ -0,0 +1,17 @@
+#include "py/mphal.h"
+
+void USBD_CDC_TxAlways(const uint8_t *buf, uint32_t len);
+int USBD_CDC_Rx(uint8_t *buf, uint32_t len, uint32_t timeout);
+
+int mp_hal_stdin_rx_chr(void) {
+    for (;;) {
+        byte c;
+        if (USBD_CDC_Rx(&c, 1, 0) != 0) {
+            return c;
+        }
+    }
+}
+
+void mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    USBD_CDC_TxAlways((const uint8_t*)str, len);
+}
diff --git a/micropython/firmware/mphalport.h b/micropython/firmware/mphalport.h
index 0db02a8c..ef957457 100644
--- a/micropython/firmware/mphalport.h
+++ b/micropython/firmware/mphalport.h
@@ -1 +1,11 @@
-static inline void mp_hal_set_interrupt_char(char c) {}
+#include STM32_HAL_H
+
+#include "lib/utils/interrupt_char.h"
+
+#define MP_HAL_UNIQUE_ID_ADDRESS (0x1fff7a10)
+
+#define MP_PLAT_PRINT_STRN(str, len) mp_hal_stdout_tx_strn_cooked(str, len)
+
+static inline mp_uint_t mp_hal_ticks_cpu(void) {
+    return DWT->CYCCNT;
+}