add a check key command

`VDU 23,0,&99,virtualkey`

prompts a new keycode data packet to be sent to MOS with latest state of `virtualkey`

Author: stevesims

video/agon.h

@@ -64,6 +64,7 @@
 #define VDP_FONT				0x95	// Font management commands
 #define VDP_AFFINE_TRANSFORM	0x96	// Set affine transform
 #define VDP_CONTROLKEYS			0x98	// Control keys on/off
+#define VDP_CHECKKEY			0x99	// Request updated keyboard data for a key
 #define VDP_BUFFER_PRINT		0x9B	// Print a buffer of characters literally with no command interpretation
 #define VDP_TEXT_VIEWPORT		0x9C	// Set text viewport using current graphics coordinates
 #define VDP_GRAPHICS_VIEWPORT	0x9D	// Set graphics viewport using current graphics coordinates

video/agon_ps2.h

@@ -110,7 +110,7 @@ bool getKeyboardKey(uint8_t *keycode, uint8_t *modifiers, uint8_t *vk, uint8_t *
 			return true;			
 		}
 	}
-	
+
 	if (kb->getNextVirtualKey(&item, 0)) {
 		if (item.down) {
 			switch (item.vk) {
@@ -133,7 +133,7 @@ bool getKeyboardKey(uint8_t *keycode, uint8_t *modifiers, uint8_t *vk, uint8_t *
 					_keycode = 0x7F;
 					break;
 				default:
-					_keycode = item.ASCII;	
+					_keycode = item.ASCII;
 					break;
 			}
 			// Pack the modifiers into a byte

video/vdu_sys.h

@@ -255,6 +255,14 @@ void VDUStreamProcessor::vdu_sys_video() {
 				controlKeys = (bool) b;
 			}
 		}	break;
+		case VDP_CHECKKEY: {
+			auto key = readByte_t();	// VDU 23, 0, &99, virtualkey
+			if (key == -1) return;
+			// Inject an updated virtual key event for a key, forcing a new keycode packet to be sent
+			// NB must use a virtual key here, as we can't convert a keycode to a virtual key
+			auto keyboard = getKeyboard();
+			keyboard->injectVirtualKey((VirtualKey) key, keyboard->isVKDown((VirtualKey) key), true);
+		}	break;
 		case VDP_BUFFER_PRINT: {		// VDU 23, 0, &9B
 			auto bufferId = readWord_t();
 			if (bufferId == -1) return;