wait for TXREADY to avoid serial transmit buffer overrun

sources/bas_printf.c

@@ -66,7 +66,7 @@ static void xputchar(int c)
 			"bsr			printf_helper\n\t"
 			/* output */:
 			/* input */: "r" (c)
-			/* clobber */: "d0","a0"
+			/* clobber */: "d0","d2","a0"
 	);
 }
 
@@ -380,3 +380,12 @@ void xvsnprintf(char *str, size_t size, const char *fmt, va_list va)
 	*xstring++ = '\0';
 }
 
+
+void display_progress()
+{
+	static int _progress_index;
+	char progress_char[] = "|/-\\";
+	xputchar(progress_char[_progress_index++ % strlen(progress_char)]);
+	xputchar('\r');
+}
+

sources/printf_helper.S

@@ -3,6 +3,10 @@
 			.global printf_helper
 printf_helper:
 			.extern		__MBAR
-			lea			__MBAR+0x860C,a0
-			move.b		d0,(a0)
+.wait_txready:
+			move.w		__MBAR+0x8604,d2	// PSCSCR0 status register
+			btst		#10,d2				// space left in TX fifo?
+			beq.s		.wait_txready		// no, loop
+			lea			__MBAR+0x860C,a0	// PSCSTB0 transmitter buffer register
+			move.b		d0,(a0)				// send byte
 			rts