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

Marlin/src/HAL/HAL_STM32/HAL.cpp

@@ -30,6 +30,7 @@
 #include "HAL.h"
 
 #include "../../inc/MarlinConfig.h"
+#include "../shared/Delay.h"
 
 #if ENABLED(EEPROM_EMULATED_WITH_SRAM)
   #if STM32F7xx
@@ -80,6 +81,11 @@ uint16_t HAL_adc_result;
 // 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

@@ -153,8 +153,6 @@ extern uint16_t HAL_adc_result;
 // Public functions
 // --------------------------------------------------------------------------
 
-
-
 // Memory related
 #define __bss_end __bss_end__
 

Marlin/src/HAL/HAL_TEENSY31_32/HAL.cpp

@@ -26,7 +26,7 @@
 #ifdef __MK20DX256__
 
 #include "HAL.h"
-#include "../Delay.h"
+#include "../shared/Delay.h"
 
 #include <Wire.h>
 

Marlin/src/HAL/shared/Delay.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * Busy wait delay cycles routines:
@@ -28,13 +29,35 @@
  *  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__)
 
+  #if __CORTEX_M == 7
+
+    // 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 enableCycleCounter() {
+      CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
+
+      // Unlock DWT.
+      DWT->LAR = 0xC5ACCE55;
+
+      DWT->CYCCNT = 0;
+      DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
+    }
+
+    FORCE_INLINE volatile uint32_t getCycleCount() { return DWT->CYCCNT; }
+
+    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":::)
@@ -80,6 +103,8 @@
     }
     #undef nop
 
+  #endif
+
 #elif defined(__AVR__)
 
   #define nop() __asm__ __volatile__("nop;\n\t":::)
@@ -144,5 +169,3 @@
 
 // Delay in microseconds
 #define DELAY_US(x) DELAY_CYCLES( (x) * (F_CPU / 1000000UL) )
-
-#endif // MARLIN_DELAY_H