gint: avoid annoying banner on return from menu on fx-CG

Instead of using GetKeyWait(), we directly call into an internal OS
function, which avoids the need to press a key before we can redraw over
the OS banner and VRAM when coming back. The disassembly to locate the
function was developed by Dr-Carlos.

We still have to redraw when coming back; getkey() will do it by
dupdate() by default, and it that's not a possibility for the
application an option to receive a special event and handle it manually
is provided.

include/gint/keyboard.h

@@ -70,7 +70,7 @@ extern "C" {
    * keyreleased() checks if the specified key is currently up and was down at
      the time of the last cleareventflips().
 
-   A typical game loop might look like. cleareventflisps() must be called
+   A typical game loop might look like. cleareventflips() must be called
    _before_ clearevents().
 
      cleareventflips();
@@ -116,13 +116,13 @@ typedef struct
 {
 	uint time	:16;	/* Time of event, unique over short periods */
 
-	uint		:3;	/* Reserved for future use */
+	uint		:2;	/* Reserved for future use */
 
 	uint mod	:1;	/* Whether modifiers are used */
 	uint shift	:1;	/* If mod=1, whether SHIFT was pressed */
 	uint alpha	:1;	/* If mod=1, whether ALPHA was pressed */
 
-	uint type	:2;	/* Type of key event */
+	uint type	:3;	/* Type of key event */
 	uint key	:8;	/* Hit key */
 
 } GPACKED(4) key_event_t;
@@ -130,10 +130,11 @@ typedef struct
 /* Keyboard event types, as in the [type] field of key_event_t */
 enum
 {
-	KEYEV_NONE = 0,		/* No event available (poll() only) */
-	KEYEV_DOWN = 1,		/* Key was pressed */
-	KEYEV_UP   = 2,		/* Key was released */
-	KEYEV_HOLD = 3,		/* A key that was pressed has been held down */
+	KEYEV_NONE   = 0,	/* No event available (poll() only) */
+	KEYEV_DOWN   = 1,	/* Key was pressed */
+	KEYEV_UP     = 2,	/* Key was released */
+	KEYEV_HOLD   = 3,	/* A key that was pressed has been held down */
+	KEYEV_OSMENU = 4,	/* We went to the main menu and back */
 };
 
 /* Keyboard frequency analysis is a runtime setting since gint 2.4. This macro
@@ -239,24 +240,29 @@ key_event_t getkey(void);
 /* The following are the option bits for getkey_opt(). */
 enum {
 	/* Enable modifiers keys */
-	GETKEY_MOD_SHIFT   = 0x01,
-	GETKEY_MOD_ALPHA   = 0x02,
+	GETKEY_MOD_SHIFT      = 0x0001,
+	GETKEY_MOD_ALPHA      = 0x0002,
 	/* SHIFT + OPTN (requires GETKEY_MOD_SHIFT) or LIGHT toggles backlight */
-	GETKEY_BACKLIGHT   = 0x04,
+	GETKEY_BACKLIGHT      = 0x0004,
 	/* MENU triggers a task switch and displays the main menu */
-	GETKEY_MENU        = 0x08,
+	GETKEY_MENU           = 0x0008,
 	/* Repeat arrow keys, or even all keys */
-	GETKEY_REP_ARROWS  = 0x10,
-	GETKEY_REP_ALL     = 0x20,
+	GETKEY_REP_ARROWS     = 0x0010,
+	GETKEY_REP_ALL        = 0x0020,
 	/* Enable custom repeat profiles; see getkey_set_repeat_profile() */
-	GETKEY_REP_PROFILE = 0x40,
+	GETKEY_REP_PROFILE    = 0x0040,
 	/* Enable application shortcuts; see getkey_set_feature_function() */
-	GETKEY_FEATURES    = 0x80,
+	GETKEY_FEATURES       = 0x0080,
+	/* After coming back from the main menu, redraw the screen with dupdate
+	   (has an effect on fx-CG 50 only) */
+	GETKEY_MENU_DUPDATE   = 0x0100,
+	/* After coming back from the main menu, send a KEYEV_OSMENU event */
+	GETKEY_MENU_EVENT     = 0x0200,
 
 	/* No modifiers */
-	GETKEY_NONE        = 0x00,
+	GETKEY_NONE           = 0x0000,
 	/* Default settings of getkey() */
-	GETKEY_DEFAULT     = 0xdf,
+	GETKEY_DEFAULT        = 0x01df,
 };
 
 /* getkey_feature_t: Custom feature function

src/kernel/osmenu.c

@@ -1,6 +1,7 @@
 #include <gint/gint.h>
 #include <gint/display.h>
 #include <gint/hardware.h>
+#include <gint/keyboard.h>
 
 #include <string.h>
 
@@ -28,6 +29,69 @@ static void __osmenu_handler(void)
 	__Timer_Deinstall(__osmenu_id);
 }
 
+#ifdef FXCG50
+typedef void (os_menu_function_t)(void);
+
+/* This method is possible thanks to reverse-engineering by Dr-Carlos.
+   <https://www.cemetech.net/forum/viewtopic.php?t=18944> */
+static os_menu_function_t *find_os_menu_function(void)
+{
+	/* Get syscall table address */
+	uint32_t addr = *(uint32_t *)0x8002007c;
+	if(addr < 0x80020070 || addr >= 0x81000000 - 0x1e58 * 4)
+		return NULL;
+
+	/* Get pointer to %1e58 SwitchToMainMenu() */
+	uint16_t const *insns = *(uint16_t const **)(addr + 0x1e58 * 4);
+	if(addr < 0x80020070 || addr >= 0x81000000)
+		return NULL;
+
+	/* Check up to 150 instructions to find the call to the internal function
+	   SaveAndOpenMainMenu(). This call is in a widget of the shape
+
+	     mov.l	GetkeyToMainFunctionReturnFlag, rX
+	     mov	#3, rY
+	     bsr	SaveAndOpenMainMenu
+	     mov.b	rY, @rX
+	     bra	<start of widget>
+	     nop */
+	for(int i = 0; i < 150; i++) {
+		/* Match: mov.l @(disp, pc), rX */
+		if((insns[i] & 0xf000) != 0xd000)
+			continue;
+		int rX = (insns[i] >> 8) & 0x0f;
+
+		/* Match: mov #3, rY */
+		if((insns[i+1] & 0xf0ff) != 0xe003)
+			continue;
+		int rY = (insns[i+1] >> 8) & 0x0f;
+
+		/* Match: bsr @(disp, pc) */
+		if((insns[i+2] & 0xf000) != 0xb000)
+			continue;
+		int disp = (insns[i+2] & 0x0fff);
+
+		/* Match: mov.b rX, @rY */
+		if((insns[i+3] != 0x2000 + (rX << 8) + (rY << 4)))
+			continue;
+
+		/* Match: bra @(_, pc) */
+		if((insns[i+4] & 0xf000) != 0xa000)
+			continue;
+
+		/* Match: nop */
+		if(insns[i+5] != 0x0009)
+			continue;
+
+		/* Return the target of the bsr instruction */
+		uint32_t fun_addr = (uint32_t)&insns[i+2] + 4 + disp * 2;
+		return (os_menu_function_t *)fun_addr;
+	}
+
+	return NULL;
+}
+#endif
+
 void gint_osmenu_native(void)
 {
 	__ClearKeyBuffer();
@@ -52,6 +116,22 @@ void gint_osmenu_native(void)
 	{
 		dst[x] = src[x];
 	}
+
+	/* Try to use the internal function directly if we could figure out its
+	   address by dynamically disassembling */
+	os_menu_function_t *fun = find_os_menu_function();
+	if(fun) {
+		fun();
+
+		/* Run an immediate keyboard update, and clear the events so that the
+		   key pressed in order to re-enter the add-in is not also processed in
+		   the application */
+		extern int keysc_tick(void);
+		keysc_tick();
+		clearevents();
+
+		return;
+	}
 	#endif
 
 	/* Mysteriously crashes when coming back; might be useful another time

src/keysc/getkey.c

@@ -4,6 +4,7 @@
 
 #include <gint/keyboard.h>
 #include <gint/drivers/keydev.h>
+#include <gint/display.h>
 #include <gint/gint.h>
 #include <gint/defs/types.h>
 
@@ -64,10 +65,17 @@ key_event_t getkey_opt(int opt, volatile int *timeout)
 			e.key == KEY_MENU && !e.shift && !e.alpha)
 		{
 			gint_osmenu();
-			continue;
+			#ifdef FXCG50
+			if(opt & GETKEY_MENU_DUPDATE)
+				dupdate();
+			#endif
+
+			if(!(opt & GETKEY_MENU_EVENT))
+				continue;
+			e.type = KEYEV_OSMENU;
 		}
 
-		if(e.type == KEYEV_DOWN || e.type == KEYEV_HOLD)
+		if(e.type != KEYEV_NONE || e.type != KEYEV_UP)
 		{
 			/* Custom global features */
 			bool accepted = false;

src/keysc/keysc.c

@@ -56,7 +56,7 @@ static void keysc_scan(uint8_t *scan)
 }
 
 /* keysc_tick(): Update the keyboard to the next state */
-static int keysc_tick(void)
+int keysc_tick(void)
 {
 	uint8_t scan[12] = { 0 };
 	keysc_scan(scan);