Fix serial and keyboard input to be non-blocking

bme280_util.z80

@@ -45,8 +45,12 @@ start:
                 call    print_str_to_lcd
 
 main:
-                call    read_char_b
+                call    read_char_b             ; never blocks now
+                jr      nc,check_quit           ; wire is idle, go look at the keyboard
                 call    parse_char
+                jr      main                    ; drain the sio while it still has data
+
+check_quit:
                 ld      c,dconio                ; direct console i/o, no echo
                 ld      e,0ffh                  ; ff polls, returning zero if no key
                 call    bdos
@@ -124,13 +128,15 @@ found_point:
                 ld      (hl),00h                ; null terminate, discarding the rest
                 ret
 
-read_char_b:
-wait:
+read_char_b:                                    ; carry set with the char in a, carry clear if nothing waiting
                 in      a,(siob_ctrl)
                 bit     0,a
-                jr      z,wait
-
+                jr      z,no_char
                 in      a,(siob_data)
+                scf                             ; flag a as a real character
+                ret
+no_char:
+                or      a                       ; clears carry, a holds status not data
                 ret
 
 parse_char:                                     ; char should be in register a