klipper/klippy/chelper/steppersync.c

// Stepper step transmit synchronization
//
// Copyright (C) 2016-2025  Kevin O'Connor <kevin@koconnor.net>
//
// This file may be distributed under the terms of the GNU GPLv3 license.

// The steppersync object is used to synchronize the output of mcu
// step commands.  The mcu can only queue a limited number of step
// commands - this code tracks when items on the mcu step queue become
// free so that new commands can be transmitted.  It also ensures the
// mcu step queue is ordered between steppers so that no stepper
// starves the other steppers of space in the mcu step queue.

#include <stddef.h> // offsetof
#include <stdlib.h> // malloc
#include <string.h> // memset
#include "compiler.h" // __visible
#include "serialqueue.h" // struct queue_message
#include "stepcompress.h" // stepcompress_flush
#include "steppersync.h" // steppersync_alloc

struct steppersync {
    // Serial port
    struct serialqueue *sq;
    struct command_queue *cq;
    // Storage for associated stepcompress objects
    struct stepcompress **sc_list;
    int sc_num;
    // Storage for list of pending move clocks
    uint64_t *move_clocks;
    int num_move_clocks;
};

// Allocate a new 'steppersync' object
struct steppersync * __visible
steppersync_alloc(struct serialqueue *sq, struct stepcompress **sc_list
                  , int sc_num, int move_num)
{
    struct steppersync *ss = malloc(sizeof(*ss));
    memset(ss, 0, sizeof(*ss));
    ss->sq = sq;
    ss->cq = serialqueue_alloc_commandqueue();

    ss->sc_list = malloc(sizeof(*sc_list)*sc_num);
    memcpy(ss->sc_list, sc_list, sizeof(*sc_list)*sc_num);
    ss->sc_num = sc_num;

    ss->move_clocks = malloc(sizeof(*ss->move_clocks)*move_num);
    memset(ss->move_clocks, 0, sizeof(*ss->move_clocks)*move_num);
    ss->num_move_clocks = move_num;

    return ss;
}

// Free memory associated with a 'steppersync' object
void __visible
steppersync_free(struct steppersync *ss)
{
    if (!ss)
        return;
    free(ss->sc_list);
    free(ss->move_clocks);
    serialqueue_free_commandqueue(ss->cq);
    free(ss);
}

// Set the conversion rate of 'print_time' to mcu clock
void __visible
steppersync_set_time(struct steppersync *ss, double time_offset
                     , double mcu_freq)
{
    int i;
    for (i=0; i<ss->sc_num; i++) {
        struct stepcompress *sc = ss->sc_list[i];
        stepcompress_set_time(sc, time_offset, mcu_freq);
    }
}

// Expire the stepcompress history before the given clock time
void __visible
steppersync_history_expire(struct steppersync *ss, uint64_t end_clock)
{
    int i;
    for (i = 0; i < ss->sc_num; i++) {
        struct stepcompress *sc = ss->sc_list[i];
        stepcompress_history_expire(sc, end_clock);
    }
}

// Implement a binary heap algorithm to track when the next available
// 'struct move' in the mcu will be available
static void
heap_replace(struct steppersync *ss, uint64_t req_clock)
{
    uint64_t *mc = ss->move_clocks;
    int nmc = ss->num_move_clocks, pos = 0;
    for (;;) {
        int child1_pos = 2*pos+1, child2_pos = 2*pos+2;
        uint64_t child2_clock = child2_pos < nmc ? mc[child2_pos] : UINT64_MAX;
        uint64_t child1_clock = child1_pos < nmc ? mc[child1_pos] : UINT64_MAX;
        if (req_clock <= child1_clock && req_clock <= child2_clock) {
            mc[pos] = req_clock;
            break;
        }
        if (child1_clock < child2_clock) {
            mc[pos] = child1_clock;
            pos = child1_pos;
        } else {
            mc[pos] = child2_clock;
            pos = child2_pos;
        }
    }
}

// Find and transmit any scheduled steps prior to the given 'move_clock'
int __visible
steppersync_flush(struct steppersync *ss, uint64_t move_clock)
{
    // Flush each stepcompress to the specified move_clock
    int i;
    for (i=0; i<ss->sc_num; i++) {
        int ret = stepcompress_flush(ss->sc_list[i], move_clock);
        if (ret)
            return ret;
    }

    // Order commands by the reqclock of each pending command
    struct list_head msgs;
    list_init(&msgs);
    for (;;) {
        // Find message with lowest reqclock
        uint64_t req_clock = MAX_CLOCK;
        struct queue_message *qm = NULL;
        for (i=0; i<ss->sc_num; i++) {
            struct stepcompress *sc = ss->sc_list[i];
            struct list_head *sc_mq = stepcompress_get_msg_queue(sc);
            if (!list_empty(sc_mq)) {
                struct queue_message *m = list_first_entry(
                    sc_mq, struct queue_message, node);
                if (m->req_clock < req_clock) {
                    qm = m;
                    req_clock = m->req_clock;
                }
            }
        }
        if (!qm || (qm->min_clock && req_clock > move_clock))
            break;

        uint64_t next_avail = ss->move_clocks[0];
        if (qm->min_clock)
            // The qm->min_clock field is overloaded to indicate that
            // the command uses the 'move queue' and to store the time
            // that move queue item becomes available.
            heap_replace(ss, qm->min_clock);
        // Reset the min_clock to its normal meaning (minimum transmit time)
        qm->min_clock = next_avail;

        // Batch this command
        list_del(&qm->node);
        list_add_tail(&qm->node, &msgs);
    }

    // Transmit commands
    if (!list_empty(&msgs))
        serialqueue_send_batch(ss->sq, ss->cq, &msgs);

    return 0;
}