diff --git a/ports/stm32/main.c b/ports/stm32/main.c
index d7afb9e4af..3ff7077ac2 100644
--- a/ports/stm32/main.c
+++ b/ports/stm32/main.c
@@ -404,7 +404,7 @@ void stm32_main(uint32_t reset_mode) {
     bool sdram_valid = true;
     UNUSED(sdram_valid);
     #if MICROPY_HW_SDRAM_STARTUP_TEST
-    sdram_valid = sdram_test(true);
+    sdram_valid = sdram_test(false);
     #endif
     #endif
     #if MICROPY_PY_THREAD
diff --git a/ports/stm32/sdram.c b/ports/stm32/sdram.c
index 514192519a..e0e3500836 100644
--- a/ports/stm32/sdram.c
+++ b/ports/stm32/sdram.c
@@ -283,52 +283,106 @@ void sdram_leave_low_power(void) {
 #pragma GCC diagnostic ignored "-Wstringop-overflow"
 #endif
 
-bool sdram_test(bool fast) {
+bool __attribute__((optimize("O0"))) sdram_test(bool exhaustive) {
     uint8_t const pattern = 0xaa;
     uint8_t const antipattern = 0x55;
     uint8_t *const mem_base = (uint8_t *)sdram_start();
 
-    /* test data bus */
-    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);
+    #if MICROPY_HW_SDRAM_TEST_FAIL_ON_ERROR
+    char error_buffer[1024];
+    #endif
+
+    #if (__DCACHE_PRESENT == 1)
+    bool i_cache_disabled = false;
+    bool d_cache_disabled = false;
+
+    // Disable caches for testing.
+    if (SCB->CCR & (uint32_t)SCB_CCR_IC_Msk) {
+        SCB_DisableICache();
+        i_cache_disabled = true;
+    }
+
+    if (SCB->CCR & (uint32_t)SCB_CCR_DC_Msk) {
+        SCB_DisableDCache();
+        d_cache_disabled = true;
+    }
+    #endif
+
+    // Test data bus
+    for (uint32_t i = 0; i < MICROPY_HW_SDRAM_MEM_BUS_WIDTH; i++) {
+        *((uint32_t *)mem_base) = (1 << i);
+        if (*((uint32_t *)mem_base) != (1 << i)) {
+            #if MICROPY_HW_SDRAM_TEST_FAIL_ON_ERROR
+            snprintf(error_buffer, sizeof(error_buffer),
+                "Data bus test failed at 0x%p expected 0x%x found 0x%lx",
+                &mem_base[0], (1 << i), ((uint32_t *)mem_base)[0]);
+            __fatal_error(error_buffer);
+            #endif
             return false;
         }
     }
 
-    /* test address bus */
-    /* Check individual address lines */
+    // Test address bus
     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]);
+            #if MICROPY_HW_SDRAM_TEST_FAIL_ON_ERROR
+            snprintf(error_buffer, sizeof(error_buffer),
+                "Address bus test failed at 0x%p expected 0x%x found 0x%x",
+                &mem_base[i], pattern, mem_base[i]);
+            __fatal_error(error_buffer);
+            #endif
             return false;
         }
     }
 
-    /* Check for aliasing (overlaping addresses) */
+    // Check for aliasing (overlaping addresses)
     mem_base[0] = antipattern;
     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]);
+            #if MICROPY_HW_SDRAM_TEST_FAIL_ON_ERROR
+            snprintf(error_buffer, sizeof(error_buffer),
+                "Address bus overlap at 0x%p expected 0x%x found 0x%x",
+                &mem_base[i], pattern, mem_base[i]);
+            __fatal_error(error_buffer);
+            #endif
             return false;
         }
     }
 
-    /* test all ram cells */
-    if (!fast) {
-        for (uint32_t i = 0; i < MICROPY_HW_SDRAM_SIZE; ++i) {
+    // Test all RAM cells
+    if (exhaustive) {
+        // Write all memory first then compare, so even if the cache
+        // is enabled, it's not just writing and reading from cache.
+        // Note: This test should also detect refresh rate issues.
+        for (uint32_t i = 0; i < MICROPY_HW_SDRAM_SIZE; i++) {
             mem_base[i] = pattern;
+        }
+
+        for (uint32_t i = 0; i < MICROPY_HW_SDRAM_SIZE; i++) {
             if (mem_base[i] != pattern) {
-                printf("address bus test failed! address (%p)\n", &mem_base[i]);
+                #if MICROPY_HW_SDRAM_TEST_FAIL_ON_ERROR
+                snprintf(error_buffer, sizeof(error_buffer),
+                    "Address bus slow test failed at 0x%p expected 0x%x found 0x%x",
+                    &mem_base[i], pattern, mem_base[i]);
+                __fatal_error(error_buffer);
+                #endif
                 return false;
             }
         }
-    } else {
-        memset(mem_base, pattern, MICROPY_HW_SDRAM_SIZE);
     }
 
+    #if (__DCACHE_PRESENT == 1)
+    // Re-enable caches if they were enabled before the test started.
+    if (i_cache_disabled) {
+        SCB_EnableICache();
+    }
+
+    if (d_cache_disabled) {
+        SCB_EnableDCache();
+    }
+    #endif
+
     return true;
 }
 
diff --git a/ports/stm32/sdram.h b/ports/stm32/sdram.h
index 773a30802f..f7a124addd 100644
--- a/ports/stm32/sdram.h
+++ b/ports/stm32/sdram.h
@@ -13,5 +13,5 @@ void *sdram_start(void);
 void *sdram_end(void);
 void sdram_enter_low_power(void);
 void sdram_leave_low_power(void);
-bool sdram_test(bool fast);
+bool sdram_test(bool exhaustive);
 #endif // __SDRAM_H__