differentiate errors while printing or detecting printer

src/gbprinter.c

 #ifdef DEBUG
     EMU_printf("%s: 0x%04x\n",  __func__, (uint16_t)r);
 #endif // DEBUG
-    return r;
+    return r | PRN_STATUS_DETECT;
 }
 
 static void win_str_helper(const char *s, uint8_t y_pos) {

src/gbprinter.h

     PRN_STATUS_TIMEOUT     = 0x200, // timeout waiting for printer response
     PRN_STATUS_NO_MAGIC    = 0x400, // printer did not respond with proper 'alive'
 
+    // status flags for user code
+    PRN_STATUS_DETECT      = 0x800, // set in gbprinter_detect
+
     // masks to check for errors
     PRN_STATUS_MASK_ERRORS = 0x7F0,
     PRN_STATUS_MASK_ANY    = 0x7FF,

src/gbprinter_error.c

 
 BANKREF(gbprinter_error)
 
-#define ERROR_BITS 11
+#define ERROR_BITS 12
+
+static const char str_ok[] = "ok";
 
 static const char str_lowbat[] = "battery too low";
 static const char str_er2[] = "unknown error";
 static const char str_cancel[] = "cancelled";
 static const char str_timeout[] = "timeout";
 static const char str_magic[] = "wrong magic byte";
+static const char str_detect[] = "@ detection";
 
 static const char * const error_strings[ERROR_BITS] = {
     str_sum, str_busy, str_full, str_untran,
     str_er0, str_er1, str_er2, str_lowbat,
-    str_cancel, str_timeout, str_magic,
+    str_cancel, str_timeout, str_magic, str_detect,
 };
 
 uint8_t gbprinter_error(enum PRN_STATUS status, char *buff) BANKED {
     if (status == PRN_STATUS_OK) {
-        sprintf(buff, "ok");
+        sprintf(buff, str_ok);
         return 2;
     }
 

src/main.c

             break;
         } else if (key_pressed(J_SELECT)) {
             enum PRN_STATUS status = gbprinter_detect();
-            if (status == PRN_STATUS_OK) {
+            if ((status & PRN_STATUS_MASK_ANY) == PRN_STATUS_OK) {
                 win_score_clear(is_black, 1);
                 list_scores(is_black);
                 status = gbprinter_screenshot(1, is_black ? PRN_PALETTE_SC_B : PRN_PALETTE_SC_W);