diff --git a/ports/stm32/Makefile b/ports/stm32/Makefile
index 5cf8be79a..24e12d669 100644
--- a/ports/stm32/Makefile
+++ b/ports/stm32/Makefile
@@ -253,6 +253,7 @@ SRC_C = \
 	spibdev.c \
 	storage.c \
 	sdcard.c \
+	sdram.c \
 	fatfs_port.c \
 	lcd.c \
 	accel.c \
@@ -305,10 +306,17 @@ ifeq ($(MCU_SERIES),$(filter $(MCU_SERIES),f4 f7 h7 l4))
 SRC_HAL += $(addprefix $(HAL_DIR)/Src/stm32$(MCU_SERIES)xx_,\
 	hal_sd.c \
 	ll_sdmmc.c \
+	ll_fmc.c \
 	ll_usb.c \
 	)
 endif
 
+ifeq ($(MCU_SERIES),$(filter $(MCU_SERIES),f4 f7 h7))
+SRC_HAL += $(addprefix $(HAL_DIR)/Src/stm32$(MCU_SERIES)xx_,\
+	hal_sdram.c \
+	)
+endif
+
 ifeq ($(CMSIS_MCU),$(filter $(CMSIS_MCU),STM32H743xx))
     SRC_HAL += $(addprefix $(HAL_DIR)/Src/stm32$(MCU_SERIES)xx_, hal_fdcan.c)
 else
diff --git a/ports/stm32/main.c b/ports/stm32/main.c
index a8600d975..eefb19b56 100644
--- a/ports/stm32/main.c
+++ b/ports/stm32/main.c
@@ -55,6 +55,7 @@
 #include "rtc.h"
 #include "storage.h"
 #include "sdcard.h"
+#include "sdram.h"
 #include "rng.h"
 #include "accel.h"
 #include "servo.h"
@@ -555,7 +556,16 @@ soft_reset:
     mp_stack_set_limit((char*)&_estack - (char*)&_heap_end - 1024);
 
     // GC init
+    #if MICROPY_HW_SDRAM_SIZE
+    sdram_init();
+    #if MICROPY_HW_SDRAM_STARTUP_TEST
+    sdram_test(true);
+    #endif
+
+    gc_init(sdram_start(), sdram_end());
+    #else
     gc_init(&_heap_start, &_heap_end);
+    #endif
 
     #if MICROPY_ENABLE_PYSTACK
     static mp_obj_t pystack[384];
diff --git a/ports/stm32/sdram.c b/ports/stm32/sdram.c
index 181a34cad..323c66b1a 100644
--- a/ports/stm32/sdram.c
+++ b/ports/stm32/sdram.c
@@ -8,14 +8,15 @@
  */
 #include <stdio.h>
 #include <stdbool.h>
-#include <stm32f4xx_hal.h>
-#include "mdefs.h"
-#include "pincfg.h"
+#include <string.h>
+#include "py/runtime.h"
+#include "py/mphal.h"
+#include "pin.h"
+#include "pin_static_af.h"
 #include "systick.h"
 #include "sdram.h"
 
-#define SDRAM_TIMEOUT       ((uint32_t)0xFFFF)
-#define REFRESH_COUNT       ((uint32_t)0x0569)   /* SDRAM refresh counter (90Mhz SD clock) */
+#define SDRAM_TIMEOUT                            ((uint32_t)0xFFFF)
 #define SDRAM_MODEREG_BURST_LENGTH_1             ((uint16_t)0x0000)
 #define SDRAM_MODEREG_BURST_LENGTH_2             ((uint16_t)0x0001)
 #define SDRAM_MODEREG_BURST_LENGTH_4             ((uint16_t)0x0002)
@@ -28,43 +29,109 @@
 #define SDRAM_MODEREG_WRITEBURST_MODE_PROGRAMMED ((uint16_t)0x0000)
 #define SDRAM_MODEREG_WRITEBURST_MODE_SINGLE     ((uint16_t)0x0200)
 
-static SDRAM_HandleTypeDef hsdram;
-static FMC_SDRAM_TimingTypeDef SDRAM_Timing;
-static FMC_SDRAM_CommandTypeDef command;
+#if defined(MICROPY_HW_FMC_SDCKE0) && defined(MICROPY_HW_FMC_SDNE0)
+#define FMC_SDRAM_BANK FMC_SDRAM_BANK1
+#define FMC_SDRAM_CMD_TARGET_BANK FMC_SDRAM_CMD_TARGET_BANK1
+#define SDRAM_START_ADDRESS 0xC0000000
+#elif defined(MICROPY_HW_FMC_SDCKE1) && defined(MICROPY_HW_FMC_SDNE1)
+#define FMC_SDRAM_BANK FMC_SDRAM_BANK2
+#define FMC_SDRAM_CMD_TARGET_BANK FMC_SDRAM_CMD_TARGET_BANK2
+#define SDRAM_START_ADDRESS 0xD0000000
+#endif
+
+#ifdef FMC_SDRAM_BANK
+
 static void sdram_init_seq(SDRAM_HandleTypeDef
         *hsdram, FMC_SDRAM_CommandTypeDef *command);
 extern void __fatal_error(const char *msg);
 
-bool sdram_init()
-{
+bool sdram_init(void) {
+    SDRAM_HandleTypeDef hsdram;
+    FMC_SDRAM_TimingTypeDef SDRAM_Timing;
+    FMC_SDRAM_CommandTypeDef command;
+
+    __HAL_RCC_FMC_CLK_ENABLE();
+
+    #if defined(MICROPY_HW_FMC_SDCKE0)
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_SDCKE0, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_SDCKE0);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_SDNE0, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_SDNE0);
+
+    #elif defined(MICROPY_HW_FMC_SDCKE1)
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_SDCKE1, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_SDCKE1);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_SDNE1, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_SDNE1);
+    #endif
+
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_SDCLK, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_SDCLK);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_SDNCAS, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_SDNCAS);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_SDNRAS, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_SDNRAS);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_SDNWE, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_SDNWE);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_BA0, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_BA0);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_BA1, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_BA1);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_NBL0, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_NBL0);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_NBL1, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_NBL1);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A0, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A0);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A1, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A1);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A2, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A2);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A3, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A3);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A4, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A4);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A5, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A5);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A6, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A6);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A7, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A7);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A8, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A8);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A9, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A9);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A10, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A10);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A11, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A11);
+    #ifdef MICROPY_HW_FMC_A12
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_A12, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_A12);
+    #endif
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D0, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D0);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D1, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D1);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D2, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D2);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D3, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D3);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D4, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D4);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D5, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D5);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D6, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D6);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D7, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D7);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D8, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D8);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D9, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D9);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D10, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D10);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D11, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D11);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D12, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D12);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D13, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D13);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D14, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D14);
+    mp_hal_pin_config_alt_static(MICROPY_HW_FMC_D15, MP_HAL_PIN_MODE_ALT, MP_HAL_PIN_PULL_NONE, STATIC_AF_FMC_D15);
+
     /* SDRAM device configuration */
     hsdram.Instance = FMC_SDRAM_DEVICE;
     /* Timing configuration for 90 Mhz of SD clock frequency (180Mhz/2) */
     /* TMRD: 2 Clock cycles */
-    SDRAM_Timing.LoadToActiveDelay    = 2;
+    SDRAM_Timing.LoadToActiveDelay    = MICROPY_HW_SDRAM_TIMING_TMRD;
     /* TXSR: min=70ns (6x11.90ns) */
-    SDRAM_Timing.ExitSelfRefreshDelay = 7;
-    /* TRAS: min=45ns (4x11.90ns) max=120k (ns) */
-    SDRAM_Timing.SelfRefreshTime      = 7;
-    /* TRC:  min=67ns (6x11.90ns) */
-    SDRAM_Timing.RowCycleDelay        = 10;
-    /* TWR:  2 Clock cycles */
-    SDRAM_Timing.WriteRecoveryTime    = 2;
-    /* TRP:  20ns => 2x11.90ns */
-    SDRAM_Timing.RPDelay              = 3;
-    /* TRCD: 20ns => 2x11.90ns */
-    SDRAM_Timing.RCDDelay             = 3;
+    SDRAM_Timing.ExitSelfRefreshDelay = MICROPY_HW_SDRAM_TIMING_TXSR;
+    /* TRAS */
+    SDRAM_Timing.SelfRefreshTime      = MICROPY_HW_SDRAM_TIMING_TRAS;
+    /* TRC */
+    SDRAM_Timing.RowCycleDelay        = MICROPY_HW_SDRAM_TIMING_TRC;
+    /* TWR */
+    SDRAM_Timing.WriteRecoveryTime    = MICROPY_HW_SDRAM_TIMING_TWR;
+    /* TRP */
+    SDRAM_Timing.RPDelay              = MICROPY_HW_SDRAM_TIMING_TRP;
+    /* TRCD */
+    SDRAM_Timing.RCDDelay             = MICROPY_HW_SDRAM_TIMING_TRCD;
 
-    hsdram.Init.SDBank             = FMC_SDRAM_BANK1;
-    hsdram.Init.RowBitsNumber      = FMC_SDRAM_ROW_BITS_NUM_12;
-    hsdram.Init.ColumnBitsNumber   = FMC_SDRAM_COLUMN_BITS_NUM_10;
-    hsdram.Init.MemoryDataWidth    = FMC_SDRAM_MEM_BUS_WIDTH_8;
-    hsdram.Init.InternalBankNumber = FMC_SDRAM_INTERN_BANKS_NUM_4;
-    hsdram.Init.CASLatency         = FMC_SDRAM_CAS_LATENCY_3;
-    hsdram.Init.WriteProtection    = FMC_SDRAM_WRITE_PROTECTION_DISABLE;
-    hsdram.Init.SDClockPeriod      = FMC_SDRAM_CLOCK_PERIOD_3;
-    hsdram.Init.ReadBurst          = FMC_SDRAM_RBURST_DISABLE;
-    hsdram.Init.ReadPipeDelay      = FMC_SDRAM_RPIPE_DELAY_1;
+    #define _FMC_INIT(x, n) x ## _ ## n
+    #define FMC_INIT(x, n) _FMC_INIT(x,  n)
+
+    hsdram.Init.SDBank             = FMC_SDRAM_BANK;
+    hsdram.Init.ColumnBitsNumber   = FMC_INIT(FMC_SDRAM_COLUMN_BITS_NUM, MICROPY_HW_SDRAM_COLUMN_BITS_NUM);
+    hsdram.Init.RowBitsNumber      = FMC_INIT(FMC_SDRAM_ROW_BITS_NUM, MICROPY_HW_SDRAM_ROW_BITS_NUM);
+    hsdram.Init.MemoryDataWidth    = FMC_INIT(FMC_SDRAM_MEM_BUS_WIDTH, MICROPY_HW_SDRAM_MEM_BUS_WIDTH);
+    hsdram.Init.InternalBankNumber = FMC_INIT(FMC_SDRAM_INTERN_BANKS_NUM, MICROPY_HW_SDRAM_INTERN_BANKS_NUM);
+    hsdram.Init.CASLatency         = FMC_INIT(FMC_SDRAM_CAS_LATENCY, MICROPY_HW_SDRAM_CAS_LATENCY);
+    hsdram.Init.SDClockPeriod      = FMC_INIT(FMC_SDRAM_CLOCK_PERIOD, MICROPY_HW_SDRAM_CLOCK_PERIOD);
+    hsdram.Init.ReadPipeDelay      = FMC_INIT(FMC_SDRAM_RPIPE_DELAY, MICROPY_HW_SDRAM_RPIPE_DELAY);
+    hsdram.Init.ReadBurst          = (MICROPY_HW_SDRAM_RBURST) ? FMC_SDRAM_RBURST_ENABLE : FMC_SDRAM_RBURST_DISABLE;
+    hsdram.Init.WriteProtection    = (MICROPY_HW_SDRAM_WRITE_PROTECTION) ? FMC_SDRAM_WRITE_PROTECTION_ENABLE : FMC_SDRAM_WRITE_PROTECTION_DISABLE;
 
     /* Initialize the SDRAM controller */
     if(HAL_SDRAM_Init(&hsdram, &SDRAM_Timing) != HAL_OK) {
@@ -75,6 +142,14 @@ bool sdram_init()
     return true;
 }
 
+void *sdram_start(void) {
+    return (void*)SDRAM_START_ADDRESS;
+}
+
+void *sdram_end(void) {
+    return (void*)(SDRAM_START_ADDRESS + MICROPY_HW_SDRAM_SIZE);
+}
+
 static void sdram_init_seq(SDRAM_HandleTypeDef
         *hsdram, FMC_SDRAM_CommandTypeDef *command)
 {
@@ -83,7 +158,7 @@ static void sdram_init_seq(SDRAM_HandleTypeDef
 
     /* Step 3:  Configure a clock configuration enable command */
     command->CommandMode           = FMC_SDRAM_CMD_CLK_ENABLE;
-    command->CommandTarget         = FMC_SDRAM_CMD_TARGET_BANK1;
+    command->CommandTarget         = FMC_SDRAM_CMD_TARGET_BANK;
     command->AutoRefreshNumber     = 1;
     command->ModeRegisterDefinition = 0;
 
@@ -95,7 +170,7 @@ static void sdram_init_seq(SDRAM_HandleTypeDef
 
     /* Step 5: Configure a PALL (precharge all) command */
     command->CommandMode           = FMC_SDRAM_CMD_PALL;
-    command->CommandTarget         = FMC_SDRAM_CMD_TARGET_BANK1;
+    command->CommandTarget         = FMC_SDRAM_CMD_TARGET_BANK;
     command->AutoRefreshNumber     = 1;
     command->ModeRegisterDefinition = 0;
 
@@ -104,7 +179,7 @@ static void sdram_init_seq(SDRAM_HandleTypeDef
 
     /* Step 6 : Configure a Auto-Refresh command */
     command->CommandMode           = FMC_SDRAM_CMD_AUTOREFRESH_MODE;
-    command->CommandTarget         = FMC_SDRAM_CMD_TARGET_BANK1;
+    command->CommandTarget         = FMC_SDRAM_CMD_TARGET_BANK;
     command->AutoRefreshNumber     = 4;
     command->ModeRegisterDefinition = 0;
 
@@ -114,70 +189,77 @@ static void sdram_init_seq(SDRAM_HandleTypeDef
     /* Step 7: Program the external memory mode register */
     tmpmrd = (uint32_t)SDRAM_MODEREG_BURST_LENGTH_2   |
         SDRAM_MODEREG_BURST_TYPE_SEQUENTIAL   |
-        SDRAM_MODEREG_CAS_LATENCY_3           |
+        FMC_INIT(SDRAM_MODEREG_CAS_LATENCY, MICROPY_HW_SDRAM_CAS_LATENCY) |
         SDRAM_MODEREG_OPERATING_MODE_STANDARD |
         SDRAM_MODEREG_WRITEBURST_MODE_SINGLE;
 
     command->CommandMode           = FMC_SDRAM_CMD_LOAD_MODE;
-    command->CommandTarget         = FMC_SDRAM_CMD_TARGET_BANK1;
+    command->CommandTarget         = FMC_SDRAM_CMD_TARGET_BANK;
     command->AutoRefreshNumber     = 1;
     command->ModeRegisterDefinition = tmpmrd;
 
     /* Send the command */
     HAL_SDRAM_SendCommand(hsdram, command, 0x1000);
 
-    /* Step 8: Set the refresh rate counter */
-    /* (15.62 us x Freq) - 20 */
-    /* Set the device refresh counter */
+    /* Step 8: Set the refresh rate counter
+       RefreshRate = 64 ms / 8192 cyc = 7.8125 us/cyc
+
+       RefreshCycles = 7.8125 us * 90 MHz = 703
+       According to the formula on p.1665 of the reference manual,
+       we also need to subtract 20 from the value, so the target
+       refresh rate is 703 - 20 = 683.
+     */
+    #define REFRESH_COUNT (MICROPY_HW_SDRAM_REFRESH_RATE * 90000 / 8192 - 20)
     HAL_SDRAM_ProgramRefreshRate(hsdram, REFRESH_COUNT);
 }
 
+bool __attribute__((optimize("O0"))) sdram_test(bool fast) {
+    uint8_t const pattern = 0xaa;
+    uint8_t const antipattern = 0x55;
+    uint8_t *const mem_base = (uint8_t*)sdram_start();
 
-bool DISABLE_OPT sdram_test()
-{
-    uint8_t pattern = 0xAA;
-    uint8_t antipattern = 0x55;
-    uint32_t mem_size = (16*1024*1024);
-    uint8_t * const mem_base = (uint8_t*)0xC0000000;
-
-    printf("sdram test...\n");
     /* test data bus */
-    for (uint8_t i=1; i; i<<=1) {
+    for (uint8_t i = 1; i; i <<= 1) {
         *mem_base = i;
         if (*mem_base != i) {
             printf("data bus lines test failed! data (%d)\n", i);
-            BREAK();
+            __asm__ volatile ("BKPT");
         }
     }
 
     /* test address bus */
     /* Check individual address lines */
-    for (uint32_t i=1; i<mem_size; i<<=1) {
+    for (uint32_t i = 1; i < MICROPY_HW_SDRAM_SIZE; i <<= 1) {
         mem_base[i] = pattern;
         if (mem_base[i] != pattern) {
             printf("address bus lines test failed! address (%p)\n", &mem_base[i]);
-            BREAK();
+            __asm__ volatile ("BKPT");
         }
     }
 
     /* Check for aliasing (overlaping addresses) */
     mem_base[0] = antipattern;
-    for (uint32_t i=1; i<mem_size; i<<=1) {
+    for (uint32_t i = 1; i < MICROPY_HW_SDRAM_SIZE; i <<= 1) {
         if (mem_base[i] != pattern) {
             printf("address bus overlap %p\n", &mem_base[i]);
-            BREAK();
+            __asm__ volatile ("BKPT");
         }
     }
 
     /* test all ram cells */
-    for (uint32_t i=0; i<mem_size; i++) {
-        mem_base[i] = pattern;
-        if (mem_base[i] != pattern) {
-            printf("address bus test failed! address (%p)\n", &mem_base[i]);
-            BREAK();
+    if (!fast) {
+        for (uint32_t i = 0; i < MICROPY_HW_SDRAM_SIZE; ++i) {
+            mem_base[i] = pattern;
+            if (mem_base[i] != pattern) {
+                printf("address bus test failed! address (%p)\n", &mem_base[i]);
+                __asm__ volatile ("BKPT");
+            }
         }
+    } else {
+        memset(mem_base, pattern, MICROPY_HW_SDRAM_SIZE);
     }
 
-    printf("sdram test passed\n");
     return true;
 }
+
+#endif // FMC_SDRAM_BANK
diff --git a/ports/stm32/sdram.h b/ports/stm32/sdram.h
index f4e7915ad..9b4b4fb83 100644
--- a/ports/stm32/sdram.h
+++ b/ports/stm32/sdram.h
@@ -8,6 +8,8 @@
  */
 #ifndef __SDRAM_H__
 #define __SDRAM_H__
-bool sdram_init();
-bool sdram_test();
+bool sdram_init(void);
+void *sdram_start(void);
+void *sdram_end(void);
+bool sdram_test(bool fast);
 #endif // __SDRAM_H__