client: Explain the exponential re-send delay

[tattlekey] / client / press.h

/* tattlekey: A one-key UDP keyboard
 * Copyright (C) 2023  Scott Worley <scottworley@scottworley.com>
 *
 * 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 3 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 <https://www.gnu.org/licenses/>.
 */

#ifndef SENDS_H
#define SENDS_H

#include "pico/cyw43_arch.h"
#include "pico/util/pheap.h"
#include "pico/util/queue.h"

typedef struct {
  uint32_t timestamp;
  u16_t seq;
  u8_t send_count;
} press_t;

typedef struct {
  /* Queues of various sizes that hold presses.  There is one queue for each
   * send_count. */
  queue_t *presses;

  /* Tracks when each queue will be next ready-to-send.  Empty queues are not in
   * the heap. */
  pheap_t *sleeps_heap;

  /* The companion-array for the heap. */
  queue_t **sleeps;

} press_pile_t;

press_pile_t *create_press_pile();

/* Adds this press to the pile.
 * Copies the contents of `press`. */
void add_press(press_pile_t *pp, press_t *press);

/* When do we next need to send something (in seconds since boot)?
 * Returns -1 if there's nothing pending. */
int32_t next_scheduled_send(press_pile_t *pp);

/* Find a press ready for resend at or before `now`.
 * Move it out of the press-pile `pp` and into into `press`.
 * Or return false if there is no press due for re-send. */
bool get_press_due_for_resend(press_pile_t *pp, uint32_t now, press_t *press);

#endif