STM32F1 SPI1 bugfix (#14679)

Marlin/src/HAL/HAL_STM32F1/HAL.cpp

   #if PIN_EXISTS(LED)
     OUT_WRITE(LED_PIN, LOW);
   #endif
+  #if PIN_EXISTS(USB_CONNECT)
+    OUT_WRITE(USB_CONNECT_PIN, !USB_CONNECT_INVERTING);  // USB clear connection
+    delay(1000);                                         // Give OS time to notice
+    OUT_WRITE(USB_CONNECT_PIN, USB_CONNECT_INVERTING);
+  #endif
 }
 
 /* VGPV Done with defines

Marlin/src/HAL/HAL_STM32F1/HAL_spi_STM32F1.cpp

  * @details
  */
 void spiInit(uint8_t spiRate) {
+  /**
+   * STM32F1 APB1 = 72MHz, APB2 = 36MHz, max SPI speed of this MCU if 18Mhz 
+   * STM32F1 has 3 SPI ports, SPI1 in APB1, SPI2/SPI3 in APB2
+   * so the minimum prescale of SPI1 is DIV4, SPI2/SPI3 is DIV2
+   */
+  #if SPI_DEVICE == 1
+    #define SPI_CLOCK_MAX SPI_CLOCK_DIV4
+  #else
+    #define SPI_CLOCK_MAX SPI_CLOCK_DIV2
+  #endif
   uint8_t  clock;
   switch (spiRate) {
-    case SPI_FULL_SPEED:    clock = SPI_CLOCK_DIV2 ; break;
+    case SPI_FULL_SPEED:    clock = SPI_CLOCK_MAX ;  break;
     case SPI_HALF_SPEED:    clock = SPI_CLOCK_DIV4 ; break;
     case SPI_QUARTER_SPEED: clock = SPI_CLOCK_DIV8 ; break;
     case SPI_EIGHTH_SPEED:  clock = SPI_CLOCK_DIV16; break;
     case SPI_SPEED_5:       clock = SPI_CLOCK_DIV32; break;
     case SPI_SPEED_6:       clock = SPI_CLOCK_DIV64; break;
-    default:                clock = SPI_CLOCK_DIV2; // Default from the SPI library
+    default:                clock = SPI_CLOCK_DIV2;  // Default from the SPI library
   }
   SPI.setModule(SPI_DEVICE);
   SPI.begin();

Marlin/src/pins/stm32/pins_BIGTREE_SKR_E3_DIP.h

 //
 // USB connect control
 //
-#define USB_CONNECT        PC13
+#define USB_CONNECT_PIN    PC13
 #define USB_CONNECT_INVERTING false
 
 #define SD_DETECT_PIN      PC4

Marlin/src/pins/stm32/pins_BIGTREE_SKR_MINI_E3.h

  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 #ifndef TARGET_STM32F1
   #error "Oops! Select an STM32F1 board in 'Tools > Board.'"
 //
 // USB connect control
 //
-#define USB_CONNECT        PC13
+#define USB_CONNECT_PIN    PC13
 #define USB_CONNECT_INVERTING false
 
 #define SD_DETECT_PIN      PC4