Multiple, simultaneous, SPI buses handling and Smart SD mounting

Marlin/Configuration.h

@@ -1770,6 +1770,15 @@
  */
 //#define SDSUPPORT
 
+/**
+ * SD CARD: SEARCH ORDER
+ * Order in which SD-Cards should be searched on the device, if there are more than one.
+ * (see SD-Cards definitions in your pins.h file)
+ * This setting makes marlin prioritize the cards if more than one is inserted.
+ * Change only if you prefer one SD-Card over the other (maybe because it's more accessible)
+ */
+//#define SD_SEARCH_ORDER { 0, 1, 2, 3 }
+
 /**
  * SD CARD: SPI SPEED
  *

Marlin/src/HAL/AVR/HAL_SPI.cpp

@@ -34,21 +34,16 @@
 #include "../../inc/MarlinConfig.h"
 
 void spiBegin() {
+  #if !PIN_EXISTS(SS)
+    #error "SS_PIN not defined!"
+  #endif
   OUT_WRITE(SS_PIN, HIGH);
   SET_OUTPUT(SCK_PIN);
   SET_INPUT(MISO_PIN);
   SET_OUTPUT(MOSI_PIN);
 
-  #if DISABLED(SOFTWARE_SPI)
-    // SS must be in output mode even it is not chip select
-    //SET_OUTPUT(SS_PIN);
-    // set SS high - may be chip select for another SPI device
-    //#if SET_SPI_SS_HIGH
-      //WRITE(SS_PIN, HIGH);
-    //#endif
-    // set a default rate
-    spiInit(1);
-  #endif
+  // set a default rate
+  spiInit(1);
 }
 
 #if NONE(SOFTWARE_SPI, FORCE_SOFT_SPI)
@@ -249,5 +244,4 @@ void spiBegin() {
   }
 
 #endif // SOFTWARE_SPI || FORCE_SOFT_SPI
-
 #endif // __AVR__

Marlin/src/HAL/STM32/HAL.cpp

@@ -63,20 +63,35 @@ uint16_t HAL_adc_result;
 void HAL_init() {
   FastIO_init();
 
-  #if ENABLED(SDSUPPORT) && DISABLED(SDIO_SUPPORT) && (defined(SDSS) && SDSS != -1)
-    OUT_WRITE(SDSS, HIGH); // Try to set SDSS inactive before any other SPI users start up
+  #if ENABLED(SDSUPPORT) && DISABLED(SDIO_SUPPORT)
+    // Temporary measure to prevent devices on the bus trying to become master.
+    // This will be done again when the SPI device is initialized.
+    for (uint8_t dev = 0; dev < NUM_SPI_DEVICES; dev++) {
+      extDigitalWrite(CS_OF_DEV(dev), HIGH);                                                // Set CS HIGH (inactive) before other SPI users start.
+      pinMode(CS_OF_DEV(dev), OUTPUT);
+      if (IS_DEV_SD(dev) && SW_OF_SD(dev) != NC)                                            // For an SD card with a real switch, set the pin as input
+        _SET_MODE(SW_OF_SD(dev), DLV_OF_SD(dev) == LOW ? INPUT_PULLUP : INPUT_PULLDOWN);    // with the appropriate pull.
+    }
   #endif
 
   #if PIN_EXISTS(LED)
     OUT_WRITE(LED_PIN, LOW);
   #endif
 
   #if ENABLED(SRAM_EEPROM_EMULATION)
+    // Enable access to backup SRAM
     __HAL_RCC_PWR_CLK_ENABLE();
-    HAL_PWR_EnableBkUpAccess();           // Enable access to backup SRAM
+    HAL_PWR_EnableBkUpAccess();
     __HAL_RCC_BKPSRAM_CLK_ENABLE();
-    LL_PWR_EnableBkUpRegulator();         // Enable backup regulator
-    while (!LL_PWR_IsActiveFlag_BRR());   // Wait until backup regulator is initialized
+
+    // Enable backup regulator
+    LL_PWR_EnableBkUpRegulator();
+    // Wait until backup regulator is initialized
+    while (!LL_PWR_IsActiveFlag_BRR());
+  #endif
+
+  #if HAS_TMC_SW_SERIAL
+    SoftwareSerial::setInterruptPriority(SWSERIAL_TIMER_IRQ_PRIO, 0);
   #endif
 
   SetTimerInterruptPriorities();

Marlin/src/HAL/STM32/HAL.h

@@ -125,7 +125,7 @@ extern uint16_t HAL_adc_result;
 // Memory related
 #define __bss_end __bss_end__
 
-// Enable hooks into  setup for HAL
+// Enable hooks into setup for HAL
 void HAL_init();
 
 // Clear reset reason