Self test: cable hint in the test list (issue #114)

When test 3 found no signal the hint was drawn directly on the screen and
the next redraw of the test list overwrote it (only "Did Y" remained). The
waiting line of the test list now shows "Cable connected? Touch screen to
continue" instead of "Touch screen to continue", so it is redrawn with the
list. Test 3 itself already shows the signal level fail.

Tested: on a ZS407 test 3 forced to no signal through the debugger, the
hint stays visible; the tinySA BASIC self test passes all tests and ends
with "Touch screen to continue". BASIC net about -4 B flash, +4 B RAM.

sa_core.c

@@ -6476,6 +6476,7 @@ static const  char *const test_text [4] =
 static const  char *(test_fail_cause [TEST_COUNT]);
 static int test_status[TEST_COUNT];
 static int show_test_info = FALSE;
+static const char *test_hint;             // last line of the test list while waiting for a touch
 static volatile int test_wait = false;
 static float test_value;
 
@@ -6584,7 +6585,7 @@ void cell_draw_test_info(int x0, int y0)
       cell_printf(xpos, ypos, FONT_s"Self test status:");
     } else if (test_case[i].kind == TC_END) {
       if (test_wait)
-        cell_printf(xpos, ypos, FONT_s"Touch screen to continue");
+        cell_printf(xpos, ypos, FONT_s"%s", test_hint);
       continue;
     } else {
       cell_printf(xpos, ypos, FONT_s"Test %d: %s%s", i+1, test_fail_cause[i], test_text[test_status[i]] );
@@ -7153,6 +7154,7 @@ void selftest(int test)
       test_fail_cause[i] = "";
     }
     show_test_info = TRUE;
+    test_hint = "Touch screen to continue";
     test_step=0;
     test_step = setting.test_argument;
     if (test_step != 0) {
@@ -7170,9 +7172,7 @@ void selftest(int test)
       if (test_step == 2) {
         if (peakLevel < -60) {
           test_step = TEST_END;
-          ili9341_set_foreground(LCD_BRIGHT_COLOR_RED);
-          ili9341_drawstring_7x13("Signal level too low", 30, 140);
-          ili9341_drawstring_7x13("Did you connect high and low ports with cable?", 0, 210);
+          test_hint = "Cable connected? Touch screen to continue";   // drawn in the list, a direct draw was overwritten
           goto resume2;
         }