Implement DELAY_NS with CYCCNT on Cortex-M7 (#12283)

Marlin/src/HAL/HAL_STM32/HAL.cpp

 #include "HAL.h"
 
 #include "../../inc/MarlinConfig.h"
+#include "../shared/Delay.h"
 
 #if ENABLED(EEPROM_EMULATED_WITH_SRAM)
   #if STM32F7xx
 // HAL initialization task
 void HAL_init(void) {
 
+  // Needed for DELAY_NS() / DELAY_US() on CORTEX-M7
+  #if (defined(__arm__) || defined(__thumb__)) && __CORTEX_M == 7
+    enableCycleCounter();
+  #endif
+
   FastIO_init();
 
   #if ENABLED(SDSUPPORT)

Marlin/src/HAL/HAL_STM32F7/HAL.h

 // Public functions
 // --------------------------------------------------------------------------
 
-
-
 // Memory related
 #define __bss_end __bss_end__
 

Marlin/src/HAL/HAL_TEENSY31_32/HAL.cpp

 #ifdef __MK20DX256__
 
 #include "HAL.h"
-#include "../Delay.h"
+#include "../shared/Delay.h"
 
 #include <Wire.h>
 

Marlin/src/HAL/shared/Delay.h

  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * Busy wait delay cycles routines:
  *  DELAY_US(count): Delay execution in microseconds
  */
 
-#ifndef MARLIN_DELAY_H
-#define MARLIN_DELAY_H
-
 #include "../../core/macros.h"
+#include "../../core/millis_t.h"
 
 #if defined(__arm__) || defined(__thumb__)
 
-  // https://blueprints.launchpad.net/gcc-arm-embedded/+spec/delay-cycles
+  #if __CORTEX_M == 7
 
-  #define nop() __asm__ __volatile__("nop;\n\t":::)
+    // Cortex-M7 can use the cycle counter of the DWT unit
+    // http://www.anthonyvh.com/2017/05/18/cortex_m-cycle_counter/
 
-  FORCE_INLINE static void __delay_4cycles(uint32_t cy) { // +1 cycle
-    #if ARCH_PIPELINE_RELOAD_CYCLES < 2
-      #define EXTRA_NOP_CYCLES A("nop")
-    #else
-      #define EXTRA_NOP_CYCLES ""
-    #endif
+    FORCE_INLINE static void enableCycleCounter() {
+      CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
 
-    __asm__ __volatile__(
-      A(".syntax unified") // is to prevent CM0,CM1 non-unified syntax
-      L("1")
-      A("subs %[cnt],#1")
-      EXTRA_NOP_CYCLES
-      A("bne 1b")
-      : [cnt]"+r"(cy)   // output: +r means input+output
-      :                 // input:
-      : "cc"            // clobbers:
-    );
-  }
+      // Unlock DWT.
+      DWT->LAR = 0xC5ACCE55;
 
-  // Delay in cycles
-  FORCE_INLINE static void DELAY_CYCLES(uint32_t x) {
+      DWT->CYCCNT = 0;
+      DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
+    }
 
-    if (__builtin_constant_p(x)) {
-      #define MAXNOPS 4
+    FORCE_INLINE volatile uint32_t getCycleCount() { return DWT->CYCCNT; }
 
-      if (x <= (MAXNOPS)) {
-        switch (x) { case 4: nop(); case 3: nop(); case 2: nop(); case 1: nop(); }
-      }
-      else { // because of +1 cycle inside delay_4cycles
-        const uint32_t rem = (x - 1) % (MAXNOPS);
-        switch (rem) { case 3: nop(); case 2: nop(); case 1: nop(); }
-        if ((x = (x - 1) / (MAXNOPS)))
-          __delay_4cycles(x); // if need more then 4 nop loop is more optimal
+    FORCE_INLINE static void DELAY_CYCLES(const uint32_t x) {
+      const uint32_t endCycles = getCycleCount() + x;
+      while (PENDING(getCycleCount(), endCycles)) { }
+    }
+
+  #else
+
+    // https://blueprints.launchpad.net/gcc-arm-embedded/+spec/delay-cycles
+
+    #define nop() __asm__ __volatile__("nop;\n\t":::)
+
+    FORCE_INLINE static void __delay_4cycles(uint32_t cy) { // +1 cycle
+      #if ARCH_PIPELINE_RELOAD_CYCLES < 2
+        #define EXTRA_NOP_CYCLES A("nop")
+      #else
+        #define EXTRA_NOP_CYCLES ""
+      #endif
+
+      __asm__ __volatile__(
+        A(".syntax unified") // is to prevent CM0,CM1 non-unified syntax
+        L("1")
+        A("subs %[cnt],#1")
+        EXTRA_NOP_CYCLES
+        A("bne 1b")
+        : [cnt]"+r"(cy)   // output: +r means input+output
+        :                 // input:
+        : "cc"            // clobbers:
+      );
+    }
+
+    // Delay in cycles
+    FORCE_INLINE static void DELAY_CYCLES(uint32_t x) {
+
+      if (__builtin_constant_p(x)) {
+        #define MAXNOPS 4
+
+        if (x <= (MAXNOPS)) {
+          switch (x) { case 4: nop(); case 3: nop(); case 2: nop(); case 1: nop(); }
+        }
+        else { // because of +1 cycle inside delay_4cycles
+          const uint32_t rem = (x - 1) % (MAXNOPS);
+          switch (rem) { case 3: nop(); case 2: nop(); case 1: nop(); }
+          if ((x = (x - 1) / (MAXNOPS)))
+            __delay_4cycles(x); // if need more then 4 nop loop is more optimal
+        }
+        #undef MAXNOPS
       }
-      #undef MAXNOPS
+      else if ((x >>= 2))
+        __delay_4cycles(x);
     }
-    else if ((x >>= 2))
-      __delay_4cycles(x);
-  }
-  #undef nop
+    #undef nop
+
+  #endif
 
 #elif defined(__AVR__)
 
 
 // Delay in microseconds
 #define DELAY_US(x) DELAY_CYCLES( (x) * (F_CPU / 1000000UL) )
-
-#endif // MARLIN_DELAY_H