diff --git a/README.md b/README.md
index dceefd2..4361dc0 100644
--- a/README.md
+++ b/README.md
@@ -180,6 +180,24 @@ When you select max clock, we will take the following actions:
 
 > Note that the most significant speed constraint of this project is still the TCP connection speed.
 
+
+## For OpenOCD user
+
+This project was originally designed to run on Keil, but now you can also perform firmware flash on OpenOCD.
+
+Note that if you want to use a 40MHz SPI acceleration, you need to specify the speed after the target device is connected, otherwise it will fail with the beginning.
+
+```bash
+# Run before approaching the flash command
+> adapter speed 10000
+
+# > halt
+# > flash write_image [erase] [unlock] filename [offset] [type]
+```
+
+> Keil's timing handling is somewhat different from OpenOCD's. For example, OpenOCD lacks the SWD line reset sequence before reading the `IDCODE` registers.
+
+
 ## Develop
 
 0.  Check other branches to know the latest development progress.
diff --git a/components/DAP/config/DAP_config.h b/components/DAP/config/DAP_config.h
index a9b83bb..cc1d1f4 100644
--- a/components/DAP/config/DAP_config.h
+++ b/components/DAP/config/DAP_config.h
@@ -329,10 +329,11 @@ __STATIC_INLINE void PORT_JTAG_SETUP(void)
  */
 __STATIC_INLINE void PORT_SWD_SETUP(void)
 {
-  // At this stage we do not consider whether to use SPI or GPIO.
   // We will switch to the specific mode when setting the transfer rate.
-  DAP_SPI_Init();
-  DAP_SPI_Disable();
+
+  // Now we need to set it to ordinary GPIO mode. In most implementations,
+  // the DAP will then read the status of the PIN via the `SWJ_PIN` command.
+  DAP_SPI_Deinit();
 }
 
 /**
diff --git a/components/DAP/source/DAP.c b/components/DAP/source/DAP.c
index 6079067..c4e79ab 100644
--- a/components/DAP/source/DAP.c
+++ b/components/DAP/source/DAP.c
@@ -264,6 +264,9 @@ static uint32_t DAP_ResetTarget(uint8_t *response) {
 //             number of bytes in request (upper 16 bits)
 static uint32_t DAP_SWJ_Pins(const uint8_t *request, uint8_t *response) {
 #if ((DAP_SWD != 0) || (DAP_JTAG != 0))
+  if (SWD_TransferSpeed == kTransfer_SPI)
+    DAP_SPI_Deinit();
+
   uint32_t value;
   uint32_t select;
   uint32_t wait;
@@ -356,6 +359,9 @@ static uint32_t DAP_SWJ_Pins(const uint8_t *request, uint8_t *response) {
   *response = 0U;
 #endif
 
+  if (SWD_TransferSpeed == kTransfer_SPI) // restore
+    DAP_SPI_Init();
+
   return ((6U << 16) | 1U);
 }
 
@@ -505,15 +511,16 @@ static uint32_t DAP_SWD_Sequence(const uint8_t *request, uint8_t *response) {
     }
     count = (count + 7U) / 8U;
 #if (DAP_SWD != 0)
-    if ((sequence_info & SWD_SEQUENCE_DIN) != 0U) {
-      PIN_SWDIO_OUT_DISABLE();
-    } else {
-      PIN_SWDIO_OUT_ENABLE();
-    }
+    ////FIXME: ?
+    // if ((sequence_info & SWD_SEQUENCE_DIN) != 0U) {
+    //   PIN_SWDIO_OUT_DISABLE();
+    // } else {
+    //   PIN_SWDIO_OUT_ENABLE();
+    // }
     SWD_Sequence(sequence_info, request, response);
-    if (sequence_count == 0U) {
-      PIN_SWDIO_OUT_ENABLE();
-    }
+    // if (sequence_count == 0U) {
+    //   PIN_SWDIO_OUT_ENABLE();
+    // }
 #endif
     if ((sequence_info & SWD_SEQUENCE_DIN) != 0U) {
       request_count++;
diff --git a/components/DAP/source/spi_switch.c b/components/DAP/source/spi_switch.c
index 36d1d96..3ec4867 100644
--- a/components/DAP/source/spi_switch.c
+++ b/components/DAP/source/spi_switch.c
@@ -37,6 +37,11 @@ typedef enum {
  */
 void DAP_SPI_Init()
 {
+    // The driving of GPIO should be stopped,
+    // otherwise SPI has potential timing issues (This issue has been identified in OpenOCD)
+    GPIO.out_w1tc = (0x1 << 13);
+    GPIO.out_w1tc = (0x1 << 14);
+
     // Disable flash operation mode
     DAP_SPI.user.flash_mode = false;
 
@@ -145,6 +150,9 @@ __FORCEINLINE void DAP_SPI_Deinit()
     GPIO.enable_w1tc |= (0x1 << 12);
 #endif // (USE_SPI_SIO != 1)
 
+    // enable SWCLK output
+    GPIO.enable_w1ts |= (0x01 << 14);
+
     gpio_pin_reg_t pin_reg;
     GPIO.enable_w1ts |= (0x1 << 13);
     GPIO.pin[13].driver = 1; // OD output