diff --git a/FATFS/shimatta_sdio_driver/shimatta_sdio-driver.c b/FATFS/shimatta_sdio_driver/shimatta_sdio-driver.c
index 239862e..6107854 100644
--- a/FATFS/shimatta_sdio_driver/shimatta_sdio-driver.c
+++ b/FATFS/shimatta_sdio_driver/shimatta_sdio-driver.c
@@ -28,7 +28,7 @@ typedef enum {ACMD41_RESP_INIT, ACMD41_RESP_ERR, ACMD41_RESP_SDSC, ACMD41_RESP_S
 typedef enum {CMD8_RESP_TIMEOUT, CMD8_RESP_ACK, CMD8_RESP_ERR} CMD8_RESP_t;
 typedef uint8_t CID_t;
 
-void SDIO_InitModule();
+void initModuleHw();
 
 int SDIO_sendCmd(uint8_t CMD, uint32_t arg, uint8_t expectedAns);
 int SDIO_getResp(uint8_t expectedCMD, uint8_t typeOfAns, uint32_t* responseBuffer);
@@ -45,7 +45,7 @@ CMD8_RESP_t SDIO_send_CMD8();
 void initDetectandProtectionPins();
 int checkNotInserted(); // Returns 0 if inserted!
 int checkWriteProtection(); // returns 0 if write protected
-
+void switchPrescaler(uint8_t clkdiv);
 
 //BYTE rxtxbuffer[1<<BLOCKSIZE]; //Data RX and TX Buffer not needed anymore. thanks to DMA
 SDInfo_t cardInfo; // = {.type = CARD_NONE};
@@ -72,7 +72,7 @@ DSTATUS SDIO_initialize(){
     cardInfo.rca = 0;
     cardInfo.type = CARD_NONE;
 
-    SDIO_InitModule();
+    initModuleHw();
 
     initDetectandProtectionPins();
 
@@ -126,6 +126,10 @@ DSTATUS SDIO_initialize(){
     //TODO: Set 4 bit mode
     //TODO:
 
+    switchPrescaler(WORKCLK);
+
+
+
     if (checkWriteProtection()) {
         return STA_PROTECT;
     } else
@@ -168,7 +172,7 @@ DWORD __attribute__((weak)) get_fattime(){
 
 
 
-void SDIO_InitModule(){
+void initModuleHw(){
     //Init Clocks
     RCC->AHB1ENR    |= PORTCLKMASK;
     RCC->APB2ENR    |= RCC_APB2ENR_SDIOEN;
@@ -209,6 +213,15 @@ void SDIO_InitModule(){
 
 }
 
+void switchPrescaler(uint8_t clkdiv) {
+    SDIO->POWER = 0;
+    __DSB();
+    SDIO->CLKCR &= ~SDIO_CLKCR_CLKDIV; // Clear prescaler
+    SDIO->CLKCR |= (SDIO_CLKCR_CLKDIV & clkdiv); // Set bits
+    __DSB();
+    SDIO->POWER = SDIO_POWER_PWRCTRL_0 | SDIO_POWER_PWRCTRL_1;
+}
+
 
 //Send Command
 //Clear respone Flags