No need for _sync using CycCnt on each systick

teensy4/startup.c

 #define SYSTICK_EXT_FREQ 100000
 
 extern volatile uint32_t systick_cycle_count;
-#define MAGIC_VAL 5 // empiric start value syncs signif. digits to millis()
-static void systick_isr_sync(void)
-{
-	// 1st[0] tick is sync baseline CycCnt for micros()
-	if ( 0 == systick_millis_count )
-		systick_cycle_count = ARM_DWT_CYCCNT - MAGIC_VAL*F_CPU_ACTUAL/1000;
-	else 
-		_VectorsRam[15] = systick_isr; // use CORE _isr
-	systick_millis_count++;
-}
 static void configure_systick(void)
 {
 	_VectorsRam[14] = pendablesrvreq_isr;
-	_VectorsRam[15] = systick_isr_sync; // Wait for CycleCounter to sync
+	_VectorsRam[15] = systick_isr; // Wait for CycleCounter to sync
 	SYST_RVR = (SYSTICK_EXT_FREQ / 1000) - 1;
 	SYST_CVR = 0;
 	SYST_CSR = SYST_CSR_TICKINT | SYST_CSR_ENABLE;
 	SCB_SHPR3 = 0x20000000;  // Systick = priority 32
 	ARM_DEMCR |= ARM_DEMCR_TRCENA;
 	ARM_DWT_CTRL |= ARM_DWT_CTRL_CYCCNTENA; // turn on cycle counter
-	systick_cycle_count = ARM_DWT_CYCCNT; // was 0, must sync w/_isr
+	systick_cycle_count = ARM_DWT_CYCCNT; // compiled 0, corrected w/1st systick
 }