Update README.md

README.md

@@ -2,14 +2,18 @@
 
 > 64x32 is enough for everybody.
 
-Luchok is a Fantasy Console inspired by Chip-8.
+Luchok is a Fantasy Console inspired by Chip-8 (https://en.wikipedia.org/wiki/CHIP-8).
 
 # Features
 
-Screen: 64x32
-Scripting: Lua
-Sound: 440Hz square wave
-Controls: 16 buttons, labeled from 0 to F
+* Screen: 64x32
+
+* Scripting: Lua
+
+* Sound: 440Hz square wave
+
+* Controls: 16 buttons, labeled from 0 to F
+
 
 # Building
 Building luchok requires:
@@ -18,7 +22,26 @@ Building luchok requires:
 * liblua5.4-dev
 
 # Usage
-How to use it.
+The games for Luchok are written in Lua. (I prefer the .luchok extension, but the engine does not care).
+
+Every frame (60 per second) the function `vblank()` is called.
+
+The API for the fantasy console is:
+
+* `cls()` - clears the screen.
+* `draw(sprite, x, y)` - draw the array `sprite` at `x` (0-63) and `y` (0-31).
+* `draw(sprite, x, y, start, len)` - draw the array `sprite` (`len` (0-31) bytes starting from index `start`) at `x` (0-63) and `y` (0-31).
+* `rnd(limit)` - generate a random integer from 0 to `limit` (0-255).
+* `key_pressed(num)` - check if the specified key (0-15) is pressed at this frame.
+* `key_released(num)` - check if the specified key (0-15) has been released.
+* `bcd(num)` - splits the specified number (0-255), into array of its digits
+* `get_sprite(num)` - gets the built-in sprite for the specified number (0-255)
+* `delay_timer` (0-255) - decrements every frame until it hits 0
+* `sound_timer` (0-255) - decrements every frame until it hits 0, each frame it's not 0 a buzzer sounds
 
 # License
 GPL 3.
+
+
+# Author
+Roman "shinkarom" Shynkarenko (https://shinkarom.github.io).

source/script.cpp

@@ -239,6 +239,9 @@ void CallVBlank(){
 void ProcessDelayTimer(){
     lua_getglobal(lua, DELAY_TIMER_VARIABLE);
     delay_timer = lua_tointeger(lua, -1);
+    if(delay_timer < -255 || delay_timer > 255){
+        luaL_error(lua, "delay_timer must be from 0 to 255");
+    }
     lua_pop(lua, 1);
 
     if(delay_timer > 0){
@@ -255,6 +258,9 @@ void ProcessDelayTimer(){
 void ProcessSoundTimer(){
     lua_getglobal(lua, SOUND_TIMER_VARIABLE);
     sound_timer = lua_tointeger(lua, -1);
+    if(sound_timer < -255 || sound_timer > 255){
+        luaL_error(lua, "sound_timer must be from 0 to 255");
+    }
     lua_pop(lua, 1);
 
     if(sound_timer > 0){