Added sensorless homing functionality.

Use SWDO pin (silkscreen on PCB) of S42B communication pin header as active low signal to trigger endstop based on angular deviation.

Mind that connecting SWDIO to an endstop pin on the mainboard is a non-buffered direct connection to the STM32 controller on the S42B
Adjust the sensitivty for sensorless homing with #define sensorless_sensitivty. And generally do not home too fast during testing.

Also note that the repurposing of the SWDIO Pin (PA13) as sensorless homing endstop output might break the on-the-fly SWD programming.
Pressing RES(ET) on the S42B once and retry programming normally works fine. The triggering of the sensorless homing sensitivty threshold kills the on-the-fly SWD interface!).
If it does not, you will have to hold the RES(ET) button manually until "hla_swd" is shown during openOCD programming.
Releasing RES directly at this point will start the normal programming. Holding RES too long will result in a timeout.

firmware/S42BV1.0/Close_loop/src/User/main.c

@@ -1228,6 +1228,23 @@ static void MX_GPIO_Init(void)
   LL_GPIO_Init(OLED_RST_GPIO_Port, &GPIO_InitStruct);
 
 /*************************************************/
+/***************sensorless homing IO **********************************/
+// to keep SWD programming working, the pin init is done the ugly way in the sensorless homing function in stm32f0xx_it.c
+// Still, on-the-fly SWD programming might not work in all cases.
+// If this happens, you will have to hold the RES(ET) button manually until "hla_swd" is shown during openOCD programming (standard for vscode+platform.io with stlink). 
+// Releasing RES directly at this point will start the normal programming. Holding RES too long will result in a timeout.
+
+  /*
+  GPIO_InitStruct.Pin = SENSORLESS_Pin;
+  GPIO_InitStruct.Mode = LL_GPIO_MODE_OUTPUT;
+  GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;
+  GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
+  GPIO_InitStruct.Pull = LL_GPIO_PULL_UP;
+  LL_GPIO_Init(SENSORLESS_GPIO_Port, &GPIO_InitStruct);
+  */
+
+/*************************************************/
+
   GPIO_InitStruct.Pin = LED_Pin;
   GPIO_InitStruct.Mode = LL_GPIO_MODE_OUTPUT;
   GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;

firmware/S42BV1.0/Close_loop/src/User/main.h

@@ -44,6 +44,8 @@
 #define ENIN_EXTI_IRQn EXTI2_3_IRQn
 #define LED_Pin LL_GPIO_PIN_11  
 #define LED_GPIO_Port GPIOB
+#define SENSORLESS_Pin LL_GPIO_PIN_13  //PA13 SWDIO is package pin34 on LQFP38
+#define SENSORLESS_GPIO_Port GPIOA
 #define PWM1_Pin LL_GPIO_PIN_4
 #define PWM1_GPIO_Port GPIOB
 #define PWM2_Pin LL_GPIO_PIN_5
@@ -108,6 +110,9 @@
 #define KEY_Back        LL_GPIO_IsInputPinSet(KEY_Back_GPIO_Port,KEY_Back_Pin)
 #define KEY_Confirm     LL_GPIO_IsInputPinSet(KEY_Confirm_GPIO_Port,KEY_Confirm_Pin)
 
+#define SENSORLESS_H     LL_GPIO_SetOutputPin(SENSORLESS_GPIO_Port, SENSORLESS_Pin)  
+#define SENSORLESS_L     LL_GPIO_ResetOutputPin(SENSORLESS_GPIO_Port, SENSORLESS_Pin) 
+
 #define LED_H     LL_GPIO_SetOutputPin(LED_GPIO_Port, LED_Pin)  
 #define LED_L     LL_GPIO_ResetOutputPin(LED_GPIO_Port, LED_Pin) 
 #define LED_F     LL_GPIO_TogglePin(LED_GPIO_Port, LED_Pin)

firmware/S42BV1.0/Close_loop/src/User/stm32f0xx_it.c

@@ -78,6 +78,7 @@ void EXTI2_3_IRQHandler(void)
 
 void TIM6_IRQHandler(void)
 {
+  LL_GPIO_InitTypeDef GPIO_InitStruct;
   if(LL_TIM_IsActiveFlag_UPDATE(TIM6) == 1)
   {
 	LL_TIM_ClearFlag_UPDATE(TIM6);
@@ -106,16 +107,68 @@ void TIM6_IRQHandler(void)
         else measure_once_flag =0;
         yw=y+16384*wrap_count;//           
 	    e=r-yw;//误差值
+
+        // red warning LED triggering
+        // NOTE: see below sensorless homing function using also this LED for debugging
         if(e>1638){//
           e=1638;
-          LED_H;  
+          LED_H;  // if too far off (around +36deg), red light on
         }
         else if(e<-1638){
           e=-1638;
-          LED_H;  
+          LED_H;  // if too far off (around -36deg), red light on
         }else {
-            LED_L;
+          LED_L; // else red light off
         }
+
+        // *************************************************************************************************************************************
+        // sensorless homing feature via active low SWDIO pin (PA13) on S42B com-header
+        //
+        // Mind that connecting SWDIO to an endstop pin on the mainboard is a non-buffered direct connection to the STM32 controller on the S42B
+        // Adjust the sensitivty for sensorless homing with #define sensorless_sensitivty
+        // Generally, do not home too fast with this methode!
+        //
+        // Also note that the repurposing of the SWDIO Pin (PA13) as sensorless homing endstop output might break the on-the-fly SWD programming.
+        // Pressing RES(ET) on the S42B once and retry programming normally works fine. The triggering of the sensorless homing sensitivty threshold kills the on-the-fly SWD interface!).
+        // If it does not, you will have to hold the RES(ET) button manually until "hla_swd" is shown during openOCD programming. 
+        // Releasing RES directly at this point will start the normal programming. Holding RES too long will result in a timeout.
+
+        #define sensorless_sensitivty 14  // adjust sensorloess homing sensitivty here. A value of 14 is triggering the endstop for 0.3deg deviation (16384 = 360deg)
+        if(e>sensorless_sensitivty || e<-1*sensorless_sensitivty){  // triggering around 0.2deg deviation
+          //enable SWDIO (PA13) as output pin 
+
+          //TODO: this is ugly in an interrupt routine! But defining this centrally in main.c breaks SWD programming or at least the programming verification in OCD-programming mode
+
+          GPIO_InitStruct.Pin = SENSORLESS_Pin;
+          GPIO_InitStruct.Mode = LL_GPIO_MODE_OUTPUT;
+          GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;
+          GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
+          GPIO_InitStruct.Pull = LL_GPIO_PULL_UP;
+          LL_GPIO_Init(SENSORLESS_GPIO_Port, &GPIO_InitStruct);
+
+          SENSORLESS_L;  // trigger endstop by pulling pin LOW
+          LED_H;  // for debugging, trigger red LED; comment this out, if not needed
+
+        }
+        else {
+          SENSORLESS_H; // PA13 high (3.3Volt)
+          LED_L; // red LED off; comment this out, if original LED purpose is required (magnetic too strong/weak, overcurrent, 36deg limit...)
+
+          //switch PA13 back to SWDIO behavior 
+          // TODO: this is still ugly and even does not work. SWDIO functionality is not restored by a simple LL_GPIO_MODE_INPUT. 
+          // Hitting RES manually or using BOOT0 is likely always required.
+
+        /*
+          GPIO_InitStruct.Pin = SENSORLESS_Pin;
+          GPIO_InitStruct.Mode = LL_GPIO_MODE_INPUT;   //LL_GPIO_MODE_ALTERNATE also does not restore SWDIO functionality
+          GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;
+          GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
+          GPIO_InitStruct.Pull = LL_GPIO_PULL_UP;
+          LL_GPIO_Init(SENSORLESS_GPIO_Port, &GPIO_InitStruct);
+        */
+        }
+
+
         iterm+=ki*e/32;//
 		#if 1
                 if(iterm>UMAXSUM)//