Add memory barrier, optimal interrupt on-off

Disabling an ISR on ARM has 3 instructions of latency. A Memory barrier is REQUIRED to ensure proper and predictable disabling. Memory barriers are expensive, so avoid disabling if already disabled (See https://mcuoneclipse.com/2015/10/16/nvic-disabling-interrupts-on-arm-cortex-m-and-the-need-for-a-memory-barrier-instruction/)

Marlin/src/HAL/HAL_DUE/DebugMonitor_Due.cpp

@@ -46,6 +46,11 @@ static void TXBegin(void) {
   // Disable UART interrupt in NVIC
   NVIC_DisableIRQ( UART_IRQn );
 
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
+
   // Disable clock
   pmc_disable_periph_clk( ID_UART );
 

Marlin/src/HAL/HAL_DUE/HAL_timers_Due.cpp

@@ -99,6 +99,11 @@ void HAL_timer_start(const uint8_t timer_num, const uint32_t frequency) {
   // Disable interrupt, just in case it was already enabled
   NVIC_DisableIRQ(irq);
 
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
+
   // Disable timer interrupt
   tc->TC_CHANNEL[channel].TC_IDR = TC_IDR_CPCS;
 
@@ -133,6 +138,11 @@ void HAL_timer_enable_interrupt(const uint8_t timer_num) {
 void HAL_timer_disable_interrupt(const uint8_t timer_num) {
   IRQn_Type irq = TimerConfig[timer_num].IRQ_Id;
   NVIC_DisableIRQ(irq);
+
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
 }
 
 // missing from CMSIS: Check if interrupt is enabled or not

Marlin/src/HAL/HAL_DUE/MarlinSerial_Due.cpp

@@ -245,6 +245,11 @@
     // Disable UART interrupt in NVIC
     NVIC_DisableIRQ( HWUART_IRQ );
 
+    // We NEED memory barriers to ensure Interrupts are actually disabled!
+    // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+    __DSB();
+    __ISB();
+
     // Disable clock
     pmc_disable_periph_clk( HWUART_IRQ_ID );
 
@@ -290,6 +295,11 @@
     // Disable UART interrupt in NVIC
     NVIC_DisableIRQ( HWUART_IRQ );
 
+    // We NEED memory barriers to ensure Interrupts are actually disabled!
+    // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+    __DSB();
+    __ISB();
+
     pmc_disable_periph_clk( HWUART_IRQ_ID );
   }
 

Marlin/src/HAL/HAL_DUE/watchdog_Due.cpp

@@ -68,6 +68,11 @@ void watchdogSetup(void) {
       // Disable WDT interrupt (just in case, to avoid triggering it!)
       NVIC_DisableIRQ(WDT_IRQn);
 
+      // We NEED memory barriers to ensure Interrupts are actually disabled!
+      // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+      __DSB();
+      __ISB();
+
       // Initialize WDT with the given parameters
       WDT_Enable(WDT, value);
 

Marlin/src/HAL/HAL_LPC1768/HAL_timers.h

@@ -143,6 +143,11 @@ FORCE_INLINE static void HAL_timer_disable_interrupt(const uint8_t timer_num) {
     case 0: NVIC_DisableIRQ(TIMER0_IRQn); // Disable interrupt handler
     case 1: NVIC_DisableIRQ(TIMER1_IRQn); // Disable interrupt handler
   }
+
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
 }
 
 // This function is missing from CMSIS

Marlin/src/HAL/HAL_LPC1768/LPC1768_PWM.cpp

@@ -258,6 +258,11 @@ bool LPC1768_PWM_attach_pin(pin_t pin, uint32_t min /* = 1 */, uint32_t max /* =
                                  // OK to update the active table because the
                                  // ISR doesn't use any of the changed items
 
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
+
   if (ISR_table_update) //use work table if that's the newest
     temp_table = work_table;
   else
@@ -342,6 +347,11 @@ bool LPC1768_PWM_detach_pin(pin_t pin) {
 ////  interrupt controlled PWM code
   NVIC_DisableIRQ(HAL_PWM_TIMER_IRQn);
 
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
+
   if (ISR_table_update) {
     ISR_table_update = false;    // don't update yet - have another update to do
     NVIC_EnableIRQ(HAL_PWM_TIMER_IRQn);  // re-enable PWM interrupts
@@ -428,6 +438,12 @@ bool LPC1768_PWM_write(pin_t pin, uint32_t value) {
 
 ////  interrupt controlled PWM code
   NVIC_DisableIRQ(HAL_PWM_TIMER_IRQn);
+
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
+
   if (!ISR_table_update)   // use the most up to date table
     COPY_ACTIVE_TABLE;  // copy active table into work table
 
@@ -456,6 +472,11 @@ bool useable_hardware_PWM(pin_t pin) {
 
   NVIC_DisableIRQ(HAL_PWM_TIMER_IRQn);
 
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
+
   bool return_flag = false;
   for (uint8_t i = 0; i < NUM_ISR_PWMS; i++)         // see if it's already setup
     if (active_table[i].pin == pin) return_flag = true;

Marlin/src/HAL/HAL_STM32F4/HAL_timers_STM32F4.cpp

@@ -123,6 +123,11 @@ void HAL_timer_enable_interrupt(const uint8_t timer_num) {
 
 void HAL_timer_disable_interrupt(const uint8_t timer_num) {
   HAL_NVIC_DisableIRQ(timerConfig[timer_num].IRQ_Id);
+
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
 }
 
 hal_timer_t HAL_timer_get_compare(const uint8_t timer_num) {

Marlin/src/HAL/HAL_STM32F7/HAL_timers_STM32F7.cpp

@@ -127,6 +127,11 @@ void HAL_timer_enable_interrupt(const uint8_t timer_num) {
 
 void HAL_timer_disable_interrupt(const uint8_t timer_num) {
   HAL_NVIC_DisableIRQ(timerConfig[timer_num].IRQ_Id);
+
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
 }
 
 hal_timer_t HAL_timer_get_compare(const uint8_t timer_num) {

Marlin/src/HAL/HAL_TEENSY35_36/HAL_timers_Teensy.cpp

@@ -29,6 +29,22 @@
 #include "HAL.h"
 #include "HAL_timers_Teensy.h"
 
+/** \brief Instruction Synchronization Barrier
+  Instruction Synchronization Barrier flushes the pipeline in the processor,
+  so that all instructions following the ISB are fetched from cache or
+  memory, after the instruction has been completed.
+*/
+FORCE_INLINE static void __ISB(void) {
+  __asm__ __volatile__("isb 0xF":::"memory");
+}
+
+/** \brief Data Synchronization Barrier
+  This function acts as a special kind of Data Memory Barrier.
+  It completes when all explicit memory accesses before this instruction complete.
+*/
+FORCE_INLINE static void __DSB(void) {
+  __asm__ __volatile__("dsb 0xF":::"memory");
+}
 
 void HAL_timer_start(const uint8_t timer_num, const uint32_t frequency) {
   switch (timer_num) {
@@ -65,6 +81,11 @@ void HAL_timer_disable_interrupt(const uint8_t timer_num) {
     case 0: NVIC_DISABLE_IRQ(IRQ_FTM0); break;
     case 1: NVIC_DISABLE_IRQ(IRQ_FTM1); break;
   }
+
+  // We NEED memory barriers to ensure Interrupts are actually disabled!
+  // ( https://dzone.com/articles/nvic-disabling-interrupts-on-arm-cortex-m-and-the )
+  __DSB();
+  __ISB();
 }
 
 bool HAL_timer_interrupt_enabled(const uint8_t timer_num) {

Marlin/src/feature/Max7219_Debug_LEDs.cpp

@@ -73,7 +73,6 @@ static uint8_t LEDs[8] = { 0 };
 #endif
 
 void Max7219_PutByte(uint8_t data) {
-  CRITICAL_SECTION_START;
   for (uint8_t i = 8; i--;) {
     SIG_DELAY();
     WRITE(MAX7219_CLK_PIN, LOW);       // tick
@@ -84,12 +83,10 @@ void Max7219_PutByte(uint8_t data) {
     SIG_DELAY();
     data <<= 1;
   }
-  CRITICAL_SECTION_END;
 }
 
 void Max7219(const uint8_t reg, const uint8_t data) {
   SIG_DELAY();
-  CRITICAL_SECTION_START;
   WRITE(MAX7219_LOAD_PIN, LOW);  // begin
   SIG_DELAY();
   Max7219_PutByte(reg);          // specify register
@@ -99,7 +96,6 @@ void Max7219(const uint8_t reg, const uint8_t data) {
   WRITE(MAX7219_LOAD_PIN, LOW);  // and tell the chip to load the data
   SIG_DELAY();
   WRITE(MAX7219_LOAD_PIN, HIGH);
-  CRITICAL_SECTION_END;
   SIG_DELAY();
 }
 

Marlin/src/module/temperature.cpp

@@ -1085,9 +1085,7 @@ void Temperature::updateTemperaturesFromRawValues() {
     watchdog_reset();
   #endif
 
-  CRITICAL_SECTION_START;
   temp_meas_ready = false;
-  CRITICAL_SECTION_END;
 }