diff --git a/arm9/source/gamecart/spi_test.c b/arm9/source/gamecart/spi_test.c
new file mode 100644
index 0000000..3f78e61
--- /dev/null
+++ b/arm9/source/gamecart/spi_test.c
@@ -0,0 +1,116 @@
+#include "spi_test.h"
+#include "timer.h"
+#include "ui.h"
+#include "spi.h"
+
+void SPITestWaitWriteEnd(CardType type) {
+    while (SPIWaitWriteEnd(type));
+}
+
+int SPITestEraseSector(CardType type, u32 offset, u8 actualCmd) {
+    u8 cmd[4] = { actualCmd, (u8)(offset >> 16), (u8)(offset >> 8), (u8) offset };
+    if(type == NO_CHIP || type == FLASH_8MB) return 0xC8E13404;
+    
+    int res = SPIWaitWriteEnd(type);
+    
+    if( (res = SPIEnableWriting(type)) ) return res;
+    if( (res = SPIWriteRead(type, cmd, 4, NULL, 0, NULL, 0)) ) return res;
+    SPITestWaitWriteEnd(type);
+    return 0;
+}
+
+u64 SPITestEraseAll(CardType type, u32 size, u8 actualCmd, u32 eraseSize) {
+    u32 offset;
+    u64 timer = timer_start();
+    for(offset = 0; offset < size; offset += eraseSize) {
+        SPITestEraseSector(type, offset, actualCmd);
+    }
+    return timer_ticks(timer);
+}
+
+u64 SPITestWriteAll(CardType type, u32 size, u8 actualCmd, u32 pageSize, u8 *buf) {
+    memset(buf, 0, size);
+    u8 cmd[4] = { actualCmd, 0, 0, 0 };
+    u32 offset = 0;
+    u64 timer = timer_start();
+    for(offset = 0; offset < size; offset += pageSize) {
+        cmd[1] = (u8)(offset >> 16);
+        cmd[2] = (u8)(offset >> 8);
+        cmd[3] = (u8) offset;
+        SPIEnableWriting(type);
+        SPIWriteRead(type, cmd, 4, NULL, 0, buf, pageSize);
+        SPIWaitWriteEnd(type);
+    }
+    return timer_ticks(timer);
+}
+
+int SPITestBytes(CardType t, u32 id, u8 *buf, u8 byte, const char *word, u32 size) {
+    u32 offset;
+    SPIReadSaveData(t, 0, buf, size);
+    for(offset = 0; offset < size; offset++) {
+        if(buf[offset] != byte) {
+            if(word && !ShowPrompt(true, "ID: 0x%06lX\n1: Could not %s\n*0x%06lX = 0x%02hhX", id, word, offset, buf[offset])) return -1;
+            return 1;
+        }
+    }
+    return 0;
+}
+
+void SPIFlashTest(void) {
+    CardType t = ShowPrompt(true, "Does the cart have IR?") ? FLASH_512KB_INFRARED : FLASH_256KB_1;
+    u32 size;
+    u32 pageSize;
+    u32 jedecid;
+    if(SPIReadJEDECIDAndStatusReg(t, &jedecid, NULL)) return;
+    if(!ShowPrompt(true, "ID: 0x%06lX\nDo flash test on this cart?\nThis will overwrite it completely\nseveral times!", jedecid)) return;
+    size = ShowHexPrompt(0, 8, "Memory size?");
+    u8 *buf = calloc(size, 1);
+    if (buf == NULL) {
+        ShowPrompt(false, "Malloc failed!");
+        return;
+    }
+    pageSize = ShowHexPrompt(0, 8, "Page size?");
+    // method 1:
+    u64 time1 = SPITestWriteAll(t, size, 0x0A, pageSize, buf);
+    int result1 = SPITestBytes(t, jedecid, buf, 0x00, "write", size);
+    if(result1 < 0) {
+        free(buf);
+        return;
+    }
+    ShowPrompt(false, "ID: 0x%06lX\nWriting all took %llu\nError: %d", jedecid, time1, result1);
+    // method 2: Erasing
+    u8 eraseCommand;
+    u32 eraseSize;
+    for(eraseCommand = 0xC0; eraseCommand < 0xE0; eraseCommand++) {
+        ShowString("Testing %hhX", eraseCommand);
+        SPITestEraseSector(t, 0, eraseCommand);
+        SPIReadSaveData(t, 0, buf, size);
+        for(eraseSize = 0; eraseSize < size && buf[eraseSize] == 0xff; eraseSize++);
+        if(eraseSize) {
+            SPITestWriteAll(t, eraseSize, 0x02, pageSize, buf);
+            if(SPITestBytes(t, jedecid, buf, 0x00, "reset", size) < 0) {
+                free(buf);
+                return;
+            }
+
+            if(ShowPrompt(true, "ID: 0x%06lX\n0x%02hhX erased %lu bytes\nTest?", jedecid, eraseCommand, eraseSize)) {
+                u64 eraseTime = SPITestEraseAll(t, size, eraseCommand, eraseSize);
+                int eraseResult = SPITestBytes(t, jedecid, buf, 0xFF, "erase", size);
+                if(eraseResult < 0)  {
+                    free(buf);
+                    return;
+                }
+                u64 writeTime = SPITestWriteAll(t, size, 0x02, pageSize, buf);
+                int writeResult = SPITestBytes(t, jedecid, buf, 0x00, "write", size);
+                if(eraseResult < 0)  {
+                    free(buf);
+                    return;
+                }
+                ShowPrompt(false, "ID: 0x%06lX\n0x%02hhX erases %lu bytes\nErase: %llu (%d)\nWrite: %llu (%d)\nTotal: %llu", jedecid, eraseCommand, eraseSize, eraseTime, eraseResult, writeTime, writeResult, eraseTime + writeTime);
+            }
+        }
+    }
+    free(buf);
+
+}
+
diff --git a/arm9/source/gamecart/spi_test.h b/arm9/source/gamecart/spi_test.h
new file mode 100644
index 0000000..5fc89dc
--- /dev/null
+++ b/arm9/source/gamecart/spi_test.h
@@ -0,0 +1,5 @@
+#pragma once
+#include "common.h"
+#include "spi.h"
+
+void SPIFlashTest(void);