Merge pull request #385 from Defragster/patch-6

Teensy4: Startup Hooks

teensy4/startup.c

 extern void __libc_init_array(void); // C++ standard library
 
 
+void startup_default_early_hook(void) {}
+void startup_early_hook(void)		__attribute__ ((weak, alias("startup_default_early_hook")));
+void startup_default_late_hook(void) {}
+void startup_late_hook(void)		__attribute__ ((weak, alias("startup_default_late_hook")));
 __attribute__((section(".startup"), optimize("no-tree-loop-distribute-patterns"), naked))
 void ResetHandler(void)
 {
 	}
 	SNVS_HPCR |= SNVS_HPCR_RTC_EN | SNVS_HPCR_HP_TS;
 
+	startup_early_hook();
 	while (millis() < 20) ; // wait at least 20ms before starting USB
 	usb_init();
 	analog_init();
 	pwm_init();
 	tempmon_init();
 
+	startup_late_hook();
 	while (millis() < 300) ; // wait at least 300ms before calling user code
 	//printf("before C++ constructors\n");
 	__libc_init_array();