Oh Cheat!

The heart of the project is the DigiKeyboard library for Digispark. All i have to do is debounce the buttons and once one of them is stroked (after 100ms of debounce) the cheat is sent by the command

DigiKeyboard.print("cheat");

Digispark have 4 I/O pins but one of them is connected to ground by a LED. So I have 3 pins with pullups to work. The simplest way of doing that is my encoding the buttons using a matrix of diodes. Apart the zero, we have then 7 logic states to work with.

When the first key is pressed, only PB0 goes to ground. The second key makes PB2 go to ground. The third key make both go low. The fourth make PB5 go low and so on.

Unfortunately DigiKey connector disposition is a mess. The I/O pins header misses a GND and VCC what makes life tough if you want to make a plug-in board that needs power. As for this project I only needed a ground reference for the switches and then I used the PB1 pin to work as a virtual ground by using it as an output at zero level. Then I could design a board that can be plugged in directly in DigiSpark.

By the Way the name of the project is a reference to PAC MAN for MSX computers that literally screams Oh Sh** when the player is bit by a ghost whose names are:

Project Logs

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Entry for HAD 2016 prize, Phase 4: Automation
danjovic • 07/11/2016 at 20:57 • 0 comments

I've decided to apply this project to phase 4 of Hackaday 2016 prize which involves automation. This post is to clarify/complete some information required;
About the challenge:
The project was conceived for playing "GTA" game series in a PC computer by automate the entry of cheat codes composed by single keystrokes.
About the licenses/permissions:
The project is released underGPL 2.0.
About Third party licences/restrictions
The project is based on Digi-Spark board.
Copyright of information used on the article.
"Oh Sh*t!" game was property of Aackosoft International B.V. (now extinct)
"MSX" is a trademark fromASCII Corporation
"GTA San Andreas" is a trademark from Rockstar
Video: Oh Cheat! in Action
danjovic • 02/09/2016 at 17:50 • 0 comments

Here you are a small video of Oh Cheat! in action playing GTA San Andreas.
Usinga a Chinese Digispark Clone
danjovic • 02/06/2016 at 11:33 • 0 comments
The Chinese Digispark clones are very cheap and have a female USB connector which is good but they ship with RESET enabled which means that PB5 is not available for use.
To perform the change it is necessary to change the HFuse configuration of the ATTiny85.
I have used AVeRCADE with USBasp firmware for doing that, but any ISP programmer will do fine. The connections to a 10 pin are show below. However it is possible to use other methods, for example using an Arduino (link).
The command for programming the High fuse to its correct configuration is:
```
avrdude -c usbasp -p t85 -U hfuse:w:0x5f:m
```
If everything works fine you should see something like that
Standalone board design
danjovic • 01/28/2016 at 17:24 • 0 comments

I've created a standalone design for the board, single sided and using only pth components.

Extended Digispark Keyboard library

danjovic • 01/25/2016 at 23:37 • 3 comments

I've made an extension to the SendKeyStroke method of DigiKeyboard.h by adding a key down time parameter.

SendKeyStroke method now has a third parameter to allow the simulation of pressing time (in milliseconds) that the key remains pressed until is released.

void sendKeyStroke(byte keyStroke, byte modifiers, uint16_t key_down_time);

If 'key_down_time' is zero then don't release the key, it should be done manually by sendKeysStroke(0). As 'zero' means forever, the minimum press time time is 1ms and the maximum is 65535ms.

Examples:

DigiKeyboard.sendKeyStroke(KEY_B);        // Send a B to host
DigiKeyboard.sendKeyStroke(KEY_A,0,300); // Send an A to host, takes 300ms until release

DigiKeyboard.sendKeyStroke(KEY_C,0,0);    //Send a C to host and keep it pushed
DigiKeyboard.delay(2000);                 // wait 2 seconds
DigiKeyboard.sendKeyStroke(0);            // now release any key pressed.

Tried to send a pull request to original project but without success, though. Either way the extended function is below:

  void sendKeyStroke(byte keyStroke, byte modifiers, uint16_t key_down_time) {
   	while (!usbInterruptIsReady()) {
      // Note: We wait until we can send keystroke
      //       so we know the previous keystroke was
      //       sent.
    	usbPoll();
    	_delay_ms(5);
    }
    
    memset(reportBuffer, 0, sizeof(reportBuffer));
		
    reportBuffer[0] = modifiers;
    reportBuffer[1] = keyStroke;
    
    usbSetInterrupt(reportBuffer, sizeof(reportBuffer));
		
  	while (!usbInterruptIsReady()) {
      // Note: We wait until we can send keystroke
      //       so we know the previous keystroke was
      //       sent.
    	usbPoll();
    	_delay_ms(5);
    }
	
	// Pressing time (in milliseconds) that the key remains pressed
	// until is released. If is zero don't release the key (it should be
	// done manually by sendKeysStroke(0). Therefore minimum time is 1ms
	// and the maximum is 65535ms.
	if (key_down_time) {
		while (key_down_time--) {
			usbPoll();      
			_delay_ms(1);
		}
		// Now send 'no key' pressed
		memset(reportBuffer, 0, sizeof(reportBuffer));
		usbSetInterrupt(reportBuffer, sizeof(reportBuffer));	
	} 
  }

Busted!

danjovic • 01/22/2016 at 15:50 • 0 comments

I have found the problem with GTA: The game kinda sample the keyboard state, so if the key remain pressed for a few time it won't be recognized. I got that insight when I realized that sometimes the game recognized one of the keys (like A that makes the character move left).

By analyzing Digispark.h I have noticed that the SendKeyStroke function sends a key up right after the key pressed.

  void sendKeyStroke(byte keyStroke, byte modifiers) {
   	while (!usbInterruptIsReady()) {
    	usbPoll();
    	_delay_ms(5);
    } 
    memset(reportBuffer, 0, sizeof(reportBuffer));		
    reportBuffer[0] = modifiers;
    reportBuffer[1] = keyStroke;
    usbSetInterrupt(reportBuffer, sizeof(reportBuffer));
    while (!usbInterruptIsReady()) {
    	usbPoll();
    	_delay_ms(5);
    }

         /*   HERE WAS THE PROBLEM WITH GTA   */

    // This stops endlessly repeating keystrokes:  
    memset(reportBuffer, 0, sizeof(reportBuffer));      
    usbSetInterrupt(reportBuffer, sizeof(reportBuffer));
  }

To solve that without messing with the Digispark routines I have simply copied the code into my sketch and ripped off the last two lines of code that send the zero (no key).

The compiler complained about a missing definition of reportBuffer variable. Strangely enough the definition of such variable is not defined on DigiKeyboard.h. (it is defined in DigiMouse.h and DigiJoystick.h though!).

To fix it I have just created the variable and it compiled (and worked as well).

////////////////////////////////////////////////
//   __   __        _      _    _
//   \ \ / /_ _ _ _(_)__ _| |__| |___ ___
//    \ V / _` | '_| / _` | '_ \ / -_|_-<
//     \_/\__,_|_| |_\__,_|_.__/_\___/__/
//
uint8_t ticks = 0;
uint8_t lastkey = 0;
uint8_t temp, key;
uchar     reportBuffer[2];

I have also added a custom 'print' function that for each character sent to host it waits a small delay and then sends a zero (no press).

// Print a string to the host, and add a key up after a delay 
void DigiKeyboard_print ( char *str ) {
  uint8_t data;
  while (*str) {
    data = pgm_read_byte_near(ascii_to_scan_code_table + (*str++ - 8));
    sendKeyStroke_nostop(data & 0b01111111, data >> 7 ? MOD_SHIFT_RIGHT : 0);
    DigiKeyboard.delay(50);
    sendKeyStroke_nostop(0,0);
  }
}

I have fiddled with this delay and found that 20ms is not enough but 50ms is fine.

Bug Busted!!

Oh Sh**t, it's not working!
danjovic • 01/21/2016 at 13:35 • 0 comments
I still haven't figured out why do the game (GTASA) is not accepting the keystrokes, though it can really recognize some of the strokes.
I wrote my own 'print' method to put each key, then a zero but not worked. Then I've inserted a delay between keystrokes, and yet is not working. Even tried to send several zeros in between each keystroke but still no success.
```
void my_DigiKeyboard_print ( char *str ) {
  uint8_t data;
  
  while (*str) {
    data = pgm_read_byte_near(ascii_to_scan_code_table + (*str++ - 8));
    DigiKeyboard.sendKeyStroke(data & 0b01111111, data >> 7 ? MOD_SHIFT_RIGHT : 0); 
    DigiKeyboard.sendKeyStroke(0);
    DigiKeyboard.sendKeyStroke(0);
    DigiKeyboard.sendKeyStroke(0);    
    DigiKeyboard.delay(100);   
  }  
}
```
In any other application the keys are correctly injected, it is weird.. I still have more work to do.
Prototype
danjovic • 01/21/2016 at 03:16 • 0 comments

For development of the firmware I have used a protoboard
I don't have a DigiSpark here but I have a DIY clone (named Cricket)
After I have built a keyboard with tactile switches. Sadly the perfboard only have room for 6 keys but nevermind, I don't give a cheat about 7th key.