Basic delay for Max7219 on ARM

Marlin/src/feature/Max7219_Debug_LEDs.cpp

 static uint8_t LEDs[8] = { 0 };
 
 #ifdef CPU_32_BIT
-void MS_DELAY() { DELAY_1US; }  // 32-bit processors need a delay to stabilize the signal
+  // Approximate a 1µs delay on 32-bit ARM
+  void SIG_DELAY() {
+    int16_t delay_cycles = CYCLES_PER_MICROSECOND - 10;
+    while (delay_cycles >= 10) { DELAY_NOPS(6); delay_cycles -= 10; }
+    if (delay_cycles > 0) DELAY_NOPS(delay_cycles);
+  }
 #else
-  #define MS_DELAY() DELAY_3_NOP
+  // Delay for 0.1875µs (16MHz AVR) or 0.15µs (20MHz AVR)
+  #define SIG_DELAY() DELAY_3_NOP
 #endif
 
 void Max7219_PutByte(uint8_t data) {
-  CRITICAL_SECTION_START
+  CRITICAL_SECTION_START;
   for (uint8_t i = 8; i--;) {
-    MS_DELAY();
+    SIG_DELAY();
     WRITE(MAX7219_CLK_PIN, LOW);       // tick
-    MS_DELAY();
+    SIG_DELAY();
     WRITE(MAX7219_DIN_PIN, (data & 0x80) ? HIGH : LOW);  // send 1 or 0 based on data bit
-    MS_DELAY();
+    SIG_DELAY();
     WRITE(MAX7219_CLK_PIN, HIGH);      // tock
-    MS_DELAY();
+    SIG_DELAY();
     data <<= 1;
   }
-  CRITICAL_SECTION_END
+  CRITICAL_SECTION_END;
 }
 
 void Max7219(const uint8_t reg, const uint8_t data) {
-  MS_DELAY();
-  CRITICAL_SECTION_START
+  SIG_DELAY();
+  CRITICAL_SECTION_START;
   WRITE(MAX7219_LOAD_PIN, LOW);  // begin
-  MS_DELAY();
+  SIG_DELAY();
   Max7219_PutByte(reg);          // specify register
-  MS_DELAY();
+  SIG_DELAY();
   Max7219_PutByte(data);         // put data
-  MS_DELAY();
+  SIG_DELAY();
   WRITE(MAX7219_LOAD_PIN, LOW);  // and tell the chip to load the data
-  MS_DELAY();
+  SIG_DELAY();
   WRITE(MAX7219_LOAD_PIN, HIGH);
-  CRITICAL_SECTION_END
-  MS_DELAY();
+  CRITICAL_SECTION_END;
+  SIG_DELAY();
 }
 
 void Max7219_LED_Set(const uint8_t col, const uint8_t row, const bool on) {
  */
 void Max7219_idle_tasks() {
   #if MAX7219_DEBUG_STEPPER_HEAD || MAX7219_DEBUG_STEPPER_TAIL || MAX7219_DEBUG_STEPPER_QUEUE
-    CRITICAL_SECTION_START
+    CRITICAL_SECTION_START;
     #if MAX7219_DEBUG_STEPPER_HEAD || MAX7219_DEBUG_STEPPER_QUEUE
       const uint8_t head = planner.block_buffer_head;
     #endif
     #if MAX7219_DEBUG_STEPPER_TAIL || MAX7219_DEBUG_STEPPER_QUEUE
       const uint8_t tail = planner.block_buffer_tail;
     #endif
-    CRITICAL_SECTION_END
+    CRITICAL_SECTION_END;
   #endif
 
   static uint16_t refresh_cnt = 0;  // The Max7219 circuit boards available for several dollars on eBay