Merge pull request #521 from KurtE/Teensy4_debug_printf_usb

Allow cores\teensy4 printf debug optionally go to USB

teensy4/debug/printf.h

-// #define PRINT_DEBUG_STUFF
+// uncommenting the line below will enable the debug printf statements in cores\teensy4
+// by default it will print to the Serial4 TX pin at baud rate of 115200
+//#define PRINT_DEBUG_STUFF
+
+// uncommenting the line below will switch to doing outputs to USB Serial or SEREMU instead of Serial4
+// However some of the earlier print statements that happen before USB is initialized will be lost
+// if you need those outputs, better to use Serial 4.
+//#define PRINT_DEBUG_USING_USB // if both defined will try to direct stuff out USB Serial or SEREMU
 
 #ifdef PRINT_DEBUG_STUFF
 // defining printf this way breaks things like Serial.printf() in C++ :(

teensy4/debugprintf.c

 #include "avr/pgmspace.h"
 #include <stdarg.h>
 #include "imxrt.h"
+ #include "usb_desc.h"
 
 void putchar_debug(char c);
 static void puint_debug(unsigned int num);
 	printf_debug(buf + i);
 }
 
+// first is this normal Serial?
+#if defined(PRINT_DEBUG_USING_USB) && defined(CDC_STATUS_INTERFACE) && defined(CDC_DATA_INTERFACE)
+#include "usb_dev.h"
+#include "usb_serial.h"
+FLASHMEM void putchar_debug(char c)
+{
+	usb_serial_putchar(c);
+}	
+
+FLASHMEM void printf_debug_init(void) {}
+
+#elif defined(PRINT_DEBUG_USING_USB) && defined(SEREMU_INTERFACE) && !defined(CDC_STATUS_INTERFACE) && !defined(CDC_DATA_INTERFACE)
+#include "usb_dev.h"
+#include "usb_seremu.h"
+FLASHMEM void putchar_debug(char c)
+{
+	usb_seremu_putchar(c);
+}	
+
+FLASHMEM void printf_debug_init(void) {}
+
+#else
 FLASHMEM void putchar_debug(char c)
 {
 	while (!(LPUART3_STAT & LPUART_STAT_TDRE)) ; // wait
         LPUART3_BAUD = LPUART_BAUD_OSR(25) | LPUART_BAUD_SBR(8); // ~115200 baud
         LPUART3_CTRL = LPUART_CTRL_TE;
 }
-
+#endif