Aim
In certain NES games, execution of special attack moves requires pressing multiple buttons in a particular order.
For example, Teenage Mutant Ninja Turtles 3 for NES requires pressing A + B combination to execute the special attack.
Is it possible to use a single spare button (like X or Y) press to simulate pressing of the A + B combination?
Details
When executing the special attack (by actually executing the A + B
combination), we can obtain the following trace from jstest program,
$ jstest /dev/input/js0
Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:off 3:off
Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:on 3:off
Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:off 3:off
Axes: 0: 0 1: 0 Buttons: 0:off 1:off 2:off 3:off
I have modified the joydev kernel driver to implement these "state
transitions" when the Y button is pressed.
From a12297c000216e81ab2394c246a5888369ab246a Mon Sep 17 00:00:00 2001
From: Dhiru Kholia <[email protected]>
Date: Sat, 22 Apr 2017 20:37:33 +0530
Subject: [PATCH] USB gamepad hack to trigger "special attack" by a single
keypress
$ jstest /dev/input/js0
For special attack in "Teenage Mutant Ninja Turtles III: The Manhattan
Project" we require,
Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:off 3:off
Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:on 3:off
Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:off 3:off
Axes: 0: 0 1: 0 Buttons: 0:off 1:off 2:off 3:off
---
drivers/input/joydev.c | 41 +++++++++++++++++++++++++++++++++++++++--
1 file changed, 39 insertions(+), 2 deletions(-)
diff --git a/drivers/input/joydev.c b/drivers/input/joydev.c
index 29d677c..7b8f816 100644
--- a/drivers/input/joydev.c
+++ b/drivers/input/joydev.c
@@ -148,8 +148,45 @@ static void joydev_event(struct input_handle *handle,
event.time = jiffies_to_msecs(jiffies);
rcu_read_lock();
- list_for_each_entry_rcu(client, &joydev->client_list, node)
- joydev_pass_event(client, &event);
+ // B = 2, A = 1, Y = 3 (on a USB SNES gamepad)
+ list_for_each_entry_rcu(client, &joydev->client_list, node) {
+ // When Y is pressed, simulate special attack (A + B), which
+ // requires the following transitions.
+ //
+ // Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:off 3:off
+ // Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:on 3:off
+ // Axes: 0: 0 1: 0 Buttons: 0:off 1:on 2:off 3:off
+ // Axes: 0: 0 1: 0 Buttons: 0:off 1:off 2:off 3:off
+ if (event.number == 3) { // something to do with Y button
+ if (event.value == 1) { // Y press
+ // A on
+ event.type = JS_EVENT_BUTTON;
+ event.number = 1;
+ event.value = 1;
+ joydev_pass_event(client, &event);
+ // B on
+ event.type = JS_EVENT_BUTTON;
+ event.time = event.time + 80;
+ event.number = 2;
+ event.value = 1;
+ joydev_pass_event(client, &event);
+ // B off
+ event.type = JS_EVENT_BUTTON;
+ event.time = event.time + 160;
+ event.number = 2;
+ event.value = 0;
+ joydev_pass_event(client, &event);
+ // A off
+ event.time = event.time + 30;
+ event.number = 1;
+ event.value = 0;
+ joydev_pass_event(client, &event);
+ } else { // do nothing on Y unpress
+ }
+ } else {
+ joydev_pass_event(client, &event);
+ }
+ }
rcu_read_unlock();
wake_up_interruptible(&joydev->wait);
--
2.7.4
Problem
With the patched joydev driver, jstest seems to work OK (use jstest --event /dev/input/js0 to verify this). When I actually press the Y button,
it seems to emulate A + B pressing combination.
The kernel modifications seem to be OK. See the puNES-joystick-debug.patch
puNES patch for verify that the modified joystick events are successfully
reaching puNES.
However, special moves in the games do not get triggered in emulation softwares like FCEUX or puNES.
I am wondering what/where the problem is. Do I need to introduce some artifical
delay between the four joydev_pass_event calls in my patch?
Update: I added the required delays using the mdelay function but still no
joy. The actual delay doesn't seem to happen between the joydev_pass_event
calls for some unknown reason.
References
-
http://elixir.free-electrons.com/linux/latest/source/drivers/input/joydev.c
-
https://github.com/flosse/linuxconsole/blob/master/utils/jstest.c (this uses the event interface)
-
https://github.com/punesemu/puNES/blob/master/src/core/input.c (this doesn't seem to be using joydev's event interface like jstest)
-
https://github.com/punesemu/puNES/blob/master/src/gui/linux/jstick.c
-
https://www.kernel.org/doc/Documentation/input/joystick-api.txt
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