[Bug] Sending "extra" keycodes in a tapdance causes them to be sent repeatedly

[ollien]

Describe the Bug

I have a tap dance that sends certain media codes based on the number of presses on a specific key

static void tap_dance_media(qk_tap_dance_state_t *state, void *user_data) {
	switch (state->count) {
		case 1:
			tap_code(KC_MPLY);
			break;
		case 2:
			tap_code(KC_MNXT);
			break;
		case 3:
			tap_code(KC_MPRV);
			break;
	}
}

Full keymap

/*
Copyright 2020 Álvaro "Gondolindrim" Volpato <alvaro.volpato@usp.br>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include QMK_KEYBOARD_H

static void tap_dance_media(qk_tap_dance_state_t *state, void *user_data);

LEADER_EXTERNS();

enum {
	TD_END,
	TD_MEDIA
};

qk_tap_dance_action_t tap_dance_actions[] = {
	[TD_END] = ACTION_TAP_DANCE_DOUBLE(KC_END, KC_HOME),
	[TD_MEDIA] = ACTION_TAP_DANCE_FN(tap_dance_media),
};

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
   [0] = LAYOUT_all(
    KC_GRAVE,         KC_1,    KC_2,    KC_3,    KC_4,    KC_5,    KC_6,    KC_7,    KC_8,     KC_9,    KC_0,    KC_MINS,    KC_EQL,     KC_BSPC,    XXXXXXX, KC_LEAD,
    KC_TAB,           KC_Q,    KC_W,    KC_E,    KC_R,    KC_T,    KC_Y,    KC_U,    KC_I,     KC_O,    KC_P,    KC_LBRC,    KC_RBRC,    KC_BSLS,             KC_PGUP,
    KC_CAPS,          KC_A,    KC_S,    KC_D,    KC_F,    KC_G,    KC_H,    KC_J,    KC_K,     KC_L,    KC_SCLN, KC_QUOT,    XXXXXXX,    KC_ENT,              KC_PGDN,
	KC_LSFT, XXXXXXX, KC_Z,    KC_X,    KC_C,    KC_V,    KC_B,    KC_N,    KC_M,    KC_COMM,  KC_DOT,  KC_SLSH, MO(1),                  KC_UP,               TD(TD_END),
    KC_LCTL,          KC_LGUI, KC_LALT,                            KC_SPC ,                             MO(2),   KC_RCTL,    KC_LEFT,    KC_DOWN,             KC_RGHT
	),
   [1] = LAYOUT_all(
    KC_ESC,           KC_F1,      KC_F2,      KC_F3,      KC_F4,      KC_F5,      KC_F6,      KC_F7,      KC_F8,       KC_F9,      KC_F10,     KC_TRNS,    KC_TRNS,    KC_DEL,     XXXXXXX, KC_TRNS,
    KC_TRNS,          KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,     KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,             KC_HOME,
    KC_TRNS,          KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,     KC_TRNS,    KC_TRNS,    KC_TRNS,    XXXXXXX,    KC_TRNS,             KC_END,
	KC_TRNS, XXXXXXX, KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,     KC_TRNS,    KC_TRNS,    KC_TRNS,                KC_TRNS,             KC_TRNS,
    KC_TRNS,          KC_TRNS,    KC_TRNS,                            KC_TRNS,                            KC_TRNS,     RESET,      KC_TRNS,    KC_TRNS,                KC_TRNS
	),
   [2] = LAYOUT_all(
    KC_TRNS,          KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,     KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    XXXXXXX, KC_TRNS,
    KC_TRNS,          KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,     KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,             KC_VOLU,
    KC_TRNS,          KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,     KC_TRNS,    KC_TRNS,    KC_TRNS,    XXXXXXX,    KC_TRNS,             KC_VOLD,
	KC_TRNS, XXXXXXX, KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,    KC_TRNS,     KC_TRNS,    KC_TRNS,    KC_TRNS,                KC_TRNS,             TD(TD_MEDIA),
    KC_TRNS,          KC_TRNS,    KC_TRNS,                            KC_TRNS,                            KC_TRNS,     KC_TRNS,    KC_TRNS,    KC_TRNS,                KC_TRNS
	),
};

static void tap_dance_media(qk_tap_dance_state_t *state, void *user_data) {
	switch (state->count) {
		case 1:
			tap_code(KC_MPLY);
			break;
		case 2:
			tap_code(KC_MNXT);
			break;
		case 3:
			tap_code(KC_MPRV);
			break;
	}
}

void matrix_scan_user(void) {
	LEADER_DICTIONARY() {
		leading = false;
		leader_end();

		SEQ_TWO_KEYS(KC_P, KC_R) {
			tap_code(KC_PSCR);
		}

		SEQ_FIVE_KEYS(KC_R, KC_E, KC_S, KC_E, KC_T) {
			reset_keyboard();
		}
	}
}

It seems that whenever I activate any of these tapdance branches, the keys are sent repeatedly (which was verified by looking at the output of xev), rapidly pausing/unpausing music, for instance. Interestingly, this does not happen with simple keycodes like letters; those simply press/release once as expected.

I asked in the Discord and @daskygit pointed me to a similar fix they made in ChibiOS. #14643. They theorized there might be a similar bug in vusb, pointing to

qmk_firmware/tmk_core/protocol/vusb/vusb.c

Lines 282 to 284 in 5acdb4c

	if (usbInterruptIsReadyShared()) {
	usbSetInterruptShared((void *)&report, sizeof(report_extra_t));
	}

, noting that there might be a possibility of missing interrupts. The quick fix is to change that to a busy-wait to poll USB, but I'm not sure if that's a "proper" solution (and might just lead to more missed keypresses)

System Information

Keyboard: KB Elmo Sesame
Revision (if applicable):
Operating system: Fedora 35
qmk doctor output:

[~/Documents/code/qmk_firmware] nick@cubert$ qmk doctor
Ψ QMK Doctor is checking your environment.
Ψ CLI version: 1.0.0
Ψ QMK home: /home/nick/Documents/code/qmk_firmware
Ψ Detected Linux.
⚠ Missing or outdated udev rules for 'atmel-dfu' boards. Run 'sudo cp /home/nick/Documents/code/qmk_firmware/util/udev/50-qmk.rules /etc/udev/rules.d/'.
⚠ Missing or outdated udev rules for 'hid-bootloader' boards. Run 'sudo cp /home/nick/Documents/code/qmk_firmware/util/udev/50-qmk.rules /etc/udev/rules.d/'.
Ψ Git branch: master
Ψ Repo version: 0.16.9
⚠ Git has unstashed/uncommitted changes.
Ψ All dependencies are installed.
Ψ Found arm-none-eabi-gcc version 11.1.0
Ψ Found avr-gcc version 11.1.0
⚠ We do not recommend avr-gcc newer than 8. Downgrading to 8.x is recommended.
Ψ Found avrdude version 6.3
Ψ Found dfu-util version 0.11
Ψ Found dfu-programmer version 0.7.2
Ψ Submodules are up to date.
Ψ QMK is ready to go, but minor problems were found

Any keyboard related software installed?

• AutoHotKey (Windows)
• Karabiner (macOS)
• Other:

Additional Context

[fauxpark]

Add #define TAP_CODE_DELAY 10 to your config.h.

[ollien]

@fauxpark Yep - that totally worked. Thanks!