esp32.RMT

arkon.md

RE: micropython/micropython#7015

GIST: https://gist.github.com/Andrei-Pozolotin/c4b3dd041efe53cfb92cfb4de9c67267

Here is a working experimental implementation. Basic approach is:

• use piecewise interpolation for stepper motor pulse profile
• persist interpolation segments once, inside esp32.RMT.items store
• start sending pulses from items store with rmt.h | rmt_set_clk_div() and rmt.h | rmt_write_items()
• continue sending by switching between pulse patterns with rmt.h | rmt_register_tx_end_callback() system ISR

this is accomplished with addition of 2 functions to (a copy with changes:) ports/esp32/esp32_rmt.c

// RMT.store_pulses(self, item_list:list[int]) -> None
STATIC mp_obj_t esp32_rmt_store_pulses(size_t n_args, const mp_obj_t *args) {
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(args[0]);
    mp_obj_t item_list_obj = args[1];

    size_t num_items = 0;
    mp_obj_t *item_list_ptr = NULL;
    mp_obj_get_array(item_list_obj, &num_items, &item_list_ptr);

    if (num_items > self->num_items) {
        self->items = (rmt_item32_t *)m_realloc(self->items, num_items * sizeof(rmt_item32_t *));
        self->num_items = num_items;
    }
    
    for (mp_uint_t item_index = 0; item_index < num_items; item_index++) {
        self->items[item_index].val = mp_obj_get_int(item_list_ptr[item_index]);
    }
    
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(esp32_rmt_store_pulses_obj, 2, 2, esp32_rmt_store_pulses);

// RMT.issue_pulses(self, tx_ready_func:callable, item_index:int, item_count:int, clock_div:int) -> None
STATIC mp_obj_t esp32_rmt_issue_pulses(size_t n_args, const mp_obj_t *args) {
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(args[0]);
    mp_obj_t *tx_ready_fn = MP_OBJ_TO_PTR(args[1]);
    mp_uint_t item_index = mp_obj_get_int(args[2]);
    mp_uint_t item_count = mp_obj_get_int(args[3]);
    self->clock_div = mp_obj_get_int(args[4]);

    check_esp_err(rmt_set_clk_div(self->channel_id, self->clock_div));
    
    rmt_register_tx_end_callback(esp32_rmt_private_tx_end_callback, tx_ready_fn);
    
    check_esp_err(rmt_write_items(self->channel_id, self->items + item_index, item_count, false));
    
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(esp32_rmt_issue_pulses_obj, 5, 5, esp32_rmt_issue_pulses);

and the following micropython user code:

• class Planner servo-like motion planner for nema-based stepper driver
• class Ringer isr-safe ring buffer to store stepper micro-commands
• class Stepper servo-like nema-based stepper driver based on esp32.RMT driver

with core functionality expressed in: Stepper.make_rotation_one()

    def make_rotation_one(self) -> None:
        "accelerate then decelerate during single drive turn"
        plan_one = self.planner.make_plan_rotate(+1, 0.5)
        plan_two = self.planner.make_plan_rotate(-1, 0.5)
        plan_full = plan_one + plan_two + [PLAN_CMD_STOP]
        # print(f"{plan_full=}")
        self.persist_motion_plan(plan_full)
        self.transmit_reactor()  # start transmit with isr self call

and Stepper.transmit_reactor()

    def transmit_reactor(self):
        """
        function to execute stepper micro-program:
        * invoked by self "make rotation" methods for motion start
        * invoked by esp32.RMT driver "transmit ready" ISR to continue motion
        note: use isr rules https://docs.micropython.org/en/latest/reference/isr_rules.html
        """
        buffer = self.ringer
        header = buffer.ring_get()  # micro-command prefix

        if header == PLAN_CMD_RAMP:
            # micro-command parameters
            item_index = buffer.ring_get()
            item_count = buffer.ring_get()
            clock_div = buffer.ring_get()
            # start pulse sequence form rmt driver store
            self.rmt_driver.issue_pulses(# non blocking invocation
                self.transmit_function,  # this is isr setup to self
                item_index,  # place in the store
                item_count,  # pulse ramp block size
                clock_div,  # frequency for this block
            )
            self.event_cmd_ramp.set()
            return

        if header == PLAN_CMD_STOP:
            self.event_cmd_stop.set()
            return

        self.event_cmd_trap.set()  # should not happen

esp32_rmt.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2019 "Matt Trentini" <matt.trentini@gmail.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "py/runtime.h"
#include "modmachine.h"
#include "mphalport.h"
#include "modesp32.h"

#include "esp_task.h"
#include "driver/rmt.h"

// This exposes the ESP32's RMT module to MicroPython. RMT is provided by the Espressif ESP-IDF:
//
//    https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/rmt.html
//
// With some examples provided:
//
//    https://github.com/espressif/arduino-esp32/tree/master/libraries/ESP32/examples/RMT
//
// RMT allows accurate (down to 12.5ns resolution) transmit - and receive - of pulse signals.
// Originally designed to generate infrared remote control signals, the module is very
// flexible and quite easy-to-use.
//
// This current MicroPython implementation lacks some major features, notably receive pulses
// and carrier output.

// Last available RMT channel that can transmit.
#if ESP_IDF_VERSION < ESP_IDF_VERSION_VAL(4, 4, 0)
#define RMT_LAST_TX_CHANNEL (RMT_CHANNEL_MAX - 1)
#else
#define RMT_LAST_TX_CHANNEL (SOC_RMT_TX_CANDIDATES_PER_GROUP - 1)
#endif

// Forward declaration
extern const mp_obj_type_t esp32_rmt_type;

typedef struct _esp32_rmt_obj_t {
    mp_obj_base_t base;
    uint8_t channel_id;
    gpio_num_t pin;
    uint8_t clock_div;
    mp_uint_t num_items;
    rmt_item32_t *items;
    bool loop_en;
} esp32_rmt_obj_t;

// Current channel used for machine.bitstream, in the machine_bitstream_high_low_rmt
// implementation.  A value of -1 means do not use RMT.
int8_t esp32_rmt_bitstream_channel_id = RMT_LAST_TX_CHANNEL;

#if MP_TASK_COREID == 0

typedef struct _rmt_install_state_t {
    SemaphoreHandle_t handle;
    uint8_t channel_id;
    esp_err_t ret;
} rmt_install_state_t;

STATIC void rmt_install_task(void *pvParameter) {
    rmt_install_state_t *state = pvParameter;
    state->ret = rmt_driver_install(state->channel_id, 0, 0);
    xSemaphoreGive(state->handle);
    vTaskDelete(NULL);
    for (;;) {
    }
}

// Call rmt_driver_install on core 1.  This ensures that the RMT interrupt handler is
// serviced on core 1, so that WiFi (if active) does not interrupt it and cause glitches.
esp_err_t rmt_driver_install_core1(uint8_t channel_id) {
    TaskHandle_t th;
    rmt_install_state_t state;
    state.handle = xSemaphoreCreateBinary();
    state.channel_id = channel_id;
    xTaskCreatePinnedToCore(rmt_install_task, "rmt_install_task", 2048 / sizeof(StackType_t), &state, ESP_TASK_PRIO_MIN + 1, &th, 1);
    xSemaphoreTake(state.handle, portMAX_DELAY);
    vSemaphoreDelete(state.handle);
    return state.ret;
}

#else

// MicroPython runs on core 1, so we can call the RMT installer directly and its
// interrupt handler will also run on core 1.
esp_err_t rmt_driver_install_core1(uint8_t channel_id) {
    return rmt_driver_install(channel_id, 0, 0);
}

#endif

STATIC mp_obj_t esp32_rmt_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {
    static const mp_arg_t allowed_args[] = {
        { MP_QSTR_id,        MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = -1} },
        { MP_QSTR_pin,       MP_ARG_REQUIRED | MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_none} },
        { MP_QSTR_clock_div,                   MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 8} }, // 100ns resolution
        { MP_QSTR_idle_level,                  MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} }, // low voltage
        { MP_QSTR_tx_carrier,                  MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_none} }, // no carrier
    };
    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
    mp_arg_parse_all_kw_array(n_args, n_kw, all_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
    mp_uint_t channel_id = args[0].u_int;
    gpio_num_t pin_id = machine_pin_get_id(args[1].u_obj);
    mp_uint_t clock_div = args[2].u_int;
    mp_uint_t idle_level = args[3].u_bool;
    mp_obj_t tx_carrier_obj = args[4].u_obj;

    if (esp32_rmt_bitstream_channel_id >= 0 && channel_id == esp32_rmt_bitstream_channel_id) {
        mp_raise_ValueError(MP_ERROR_TEXT("channel used by bitstream"));
    }

    if (clock_div < 1 || clock_div > 255) {
        mp_raise_ValueError(MP_ERROR_TEXT("clock_div must be between 1 and 255"));
    }

    esp32_rmt_obj_t *self = m_new_obj_with_finaliser(esp32_rmt_obj_t);
    self->base.type = &esp32_rmt_type;
    self->channel_id = channel_id;
    self->pin = pin_id;
    self->clock_div = clock_div;
    self->loop_en = false;

    rmt_config_t config = {0};
    config.rmt_mode = RMT_MODE_TX;
    config.channel = (rmt_channel_t)self->channel_id;
    config.gpio_num = self->pin;
    config.mem_block_num = 1;
    config.tx_config.loop_en = 0;

    if (tx_carrier_obj != mp_const_none) {
        mp_obj_t *tx_carrier_details = NULL;
        mp_obj_get_array_fixed_n(tx_carrier_obj, 3, &tx_carrier_details);
        mp_uint_t frequency = mp_obj_get_int(tx_carrier_details[0]);
        mp_uint_t duty = mp_obj_get_int(tx_carrier_details[1]);
        mp_uint_t level = mp_obj_is_true(tx_carrier_details[2]);

        if (frequency == 0) {
            mp_raise_ValueError(MP_ERROR_TEXT("tx_carrier frequency must be >0"));
        }
        if (duty > 100) {
            mp_raise_ValueError(MP_ERROR_TEXT("tx_carrier duty must be 0..100"));
        }

        config.tx_config.carrier_en = 1;
        config.tx_config.carrier_freq_hz = frequency;
        config.tx_config.carrier_duty_percent = duty;
        config.tx_config.carrier_level = level;
    } else {
        config.tx_config.carrier_en = 0;
    }

    config.tx_config.idle_output_en = 1;
    config.tx_config.idle_level = idle_level;

    config.clk_div = self->clock_div;

    check_esp_err(rmt_config(&config));
    check_esp_err(rmt_driver_install_core1(config.channel));

    return MP_OBJ_FROM_PTR(self);
}

STATIC void esp32_rmt_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(self_in);
    if (self->pin != -1) {
        bool idle_output_en;
        rmt_idle_level_t idle_level;
        check_esp_err(rmt_get_idle_level(self->channel_id, &idle_output_en, &idle_level));
        mp_printf(print, "RMT(channel=%u, pin=%u, source_freq=%u, clock_div=%u, idle_level=%u)",
            self->channel_id, self->pin, APB_CLK_FREQ, self->clock_div, idle_level);
    } else {
        mp_printf(print, "RMT()");
    }
}

STATIC mp_obj_t esp32_rmt_deinit(mp_obj_t self_in) {
    // fixme: check for valid channel. Return exception if error occurs.
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(self_in);
    if (self->pin != -1) { // Check if channel has already been deinitialised.
        rmt_driver_uninstall(self->channel_id);
        self->pin = -1; // -1 to indicate RMT is unused
        m_free(self->items);
    }
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(esp32_rmt_deinit_obj, esp32_rmt_deinit);

// Return the source frequency.
// Currently only the APB clock (80MHz) can be used but it is possible other
// clock sources will added in the future.
STATIC mp_obj_t esp32_rmt_source_freq(mp_obj_t self_in) {
    return mp_obj_new_int(APB_CLK_FREQ);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(esp32_rmt_source_freq_obj, esp32_rmt_source_freq);

// Return the clock divider.
STATIC mp_obj_t esp32_rmt_clock_div(mp_obj_t self_in) {
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(self_in);
    return mp_obj_new_int(self->clock_div);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(esp32_rmt_clock_div_obj, esp32_rmt_clock_div);

// Query whether the channel has finished sending pulses. Takes an optional
// timeout (in milliseconds), returning true if the pulse stream has
// completed or false if they are still transmitting (or timeout is reached).
STATIC mp_obj_t esp32_rmt_wait_done(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
    static const mp_arg_t allowed_args[] = {
        { MP_QSTR_self,    MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = mp_const_none} },
        { MP_QSTR_timeout, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0} },
    };

    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
    mp_arg_parse_all(n_args, pos_args, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);

    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(args[0].u_obj);

    esp_err_t err = rmt_wait_tx_done(self->channel_id, args[1].u_int / portTICK_PERIOD_MS);
    return err == ESP_OK ? mp_const_true : mp_const_false;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_KW(esp32_rmt_wait_done_obj, 1, esp32_rmt_wait_done);

STATIC mp_obj_t esp32_rmt_loop(mp_obj_t self_in, mp_obj_t loop) {
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(self_in);
    self->loop_en = mp_obj_get_int(loop);
    if (!self->loop_en) {
        bool loop_en;
        check_esp_err(rmt_get_tx_loop_mode(self->channel_id, &loop_en));
        if (loop_en) {
            check_esp_err(rmt_set_tx_loop_mode(self->channel_id, false));
            check_esp_err(rmt_set_tx_intr_en(self->channel_id, true));
        }
    }
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_2(esp32_rmt_loop_obj, esp32_rmt_loop);

STATIC mp_obj_t esp32_rmt_write_pulses(size_t n_args, const mp_obj_t *args) {
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(args[0]);
    mp_obj_t duration_obj = args[1];
    mp_obj_t data_obj = n_args > 2 ? args[2] : mp_const_true;

    mp_uint_t duration = 0;
    size_t duration_length = 0;
    mp_obj_t *duration_ptr = NULL;
    mp_uint_t data = 0;
    size_t data_length = 0;
    mp_obj_t *data_ptr = NULL;
    mp_uint_t num_pulses = 0;

    if (!(mp_obj_is_type(data_obj, &mp_type_tuple) || mp_obj_is_type(data_obj, &mp_type_list))) {
        // Mode 1: array of durations, toggle initial data value
        mp_obj_get_array(duration_obj, &duration_length, &duration_ptr);
        data = mp_obj_is_true(data_obj);
        num_pulses = duration_length;
    } else if (mp_obj_is_int(duration_obj)) {
        // Mode 2: constant duration, array of data values
        duration = mp_obj_get_int(duration_obj);
        mp_obj_get_array(data_obj, &data_length, &data_ptr);
        num_pulses = data_length;
    } else {
        // Mode 3: arrays of durations and data values
        mp_obj_get_array(duration_obj, &duration_length, &duration_ptr);
        mp_obj_get_array(data_obj, &data_length, &data_ptr);
        if (duration_length != data_length) {
            mp_raise_ValueError(MP_ERROR_TEXT("duration and data must have same length"));
        }
        num_pulses = duration_length;
    }

    if (num_pulses == 0) {
        mp_raise_ValueError(MP_ERROR_TEXT("No pulses"));
    }
    if (self->loop_en && num_pulses > 126) {
        mp_raise_ValueError(MP_ERROR_TEXT("Too many pulses for loop"));
    }

    mp_uint_t num_items = (num_pulses / 2) + (num_pulses % 2);
    if (num_items > self->num_items) {
        self->items = (rmt_item32_t *)m_realloc(self->items, num_items * sizeof(rmt_item32_t *));
        self->num_items = num_items;
    }

    for (mp_uint_t item_index = 0, pulse_index = 0; item_index < num_items; item_index++) {
        self->items[item_index].duration0 = duration_length ? mp_obj_get_int(duration_ptr[pulse_index]) : duration;
        self->items[item_index].level0 = data_length ? mp_obj_is_true(data_ptr[pulse_index]) : data++;
        pulse_index++;
        if (pulse_index < num_pulses) {
            self->items[item_index].duration1 = duration_length ? mp_obj_get_int(duration_ptr[pulse_index]) : duration;
            self->items[item_index].level1 = data_length ? mp_obj_is_true(data_ptr[pulse_index]) : data++;
            pulse_index++;
        } else {
            self->items[item_index].duration1 = 0;
            self->items[item_index].level1 = 0;
        }
    }

    if (self->loop_en) {
        bool loop_en;
        check_esp_err(rmt_get_tx_loop_mode(self->channel_id, &loop_en));
        if (loop_en) {
            check_esp_err(rmt_set_tx_intr_en(self->channel_id, true));
            check_esp_err(rmt_set_tx_loop_mode(self->channel_id, false));
        }
        check_esp_err(rmt_wait_tx_done(self->channel_id, portMAX_DELAY));
    }

    check_esp_err(rmt_write_items(self->channel_id, self->items, num_items, false));

    if (self->loop_en) {
        check_esp_err(rmt_set_tx_intr_en(self->channel_id, false));
        check_esp_err(rmt_set_tx_loop_mode(self->channel_id, true));
    }

    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(esp32_rmt_write_pulses_obj, 2, 3, esp32_rmt_write_pulses);

// USER

// RMT.store_pulses(self, item_list:list[int32]) -> None
STATIC mp_obj_t esp32_rmt_store_pulses(size_t n_args, const mp_obj_t *args) {
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(args[0]);
    mp_obj_t item_list_obj = args[1];

    size_t num_items = 0;
    mp_obj_t *item_list_ptr = NULL;
    mp_obj_get_array(item_list_obj, &num_items, &item_list_ptr);

    if (num_items > self->num_items) {
        self->items = (rmt_item32_t *)m_realloc(self->items, num_items * sizeof(rmt_item32_t *));
        self->num_items = num_items;
    }
    
    for (mp_uint_t item_index = 0; item_index < num_items; item_index++) {
        self->items[item_index].val = mp_obj_get_int(item_list_ptr[item_index]);
    }
    
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(esp32_rmt_store_pulses_obj, 2, 2, esp32_rmt_store_pulses);

#include "py/gc.h"
#include "py/mpthread.h"
#include "py/stackctrl.h"

// called from esp32 RMT system ISR provided by rmt_driver_install()
STATIC void esp32_rmt_private_tx_end_callback(rmt_channel_t channel, void *arg) {

    void *state_past = mp_thread_get_state();
    mp_state_thread_t state_next;
    mp_thread_set_state(&state_next);
    
    mp_stack_set_top(&state_next + 1);
    mp_stack_set_limit(1024);
    
    mp_locals_set(mp_state_ctx.thread.dict_locals);
    mp_globals_set(mp_state_ctx.thread.dict_globals);
    
    mp_sched_lock();
    gc_lock();

    mp_obj_t *tx_ready_fn = (mp_obj_t *) arg;
    mp_call_function_0(tx_ready_fn);
    
    gc_unlock();
    mp_sched_unlock();
    mp_thread_set_state(state_past);
    
}

// RMT.issue_pulses(self, tx_ready_func:callable, item_index:int, item_count:int, clock_div:int) -> None
STATIC mp_obj_t esp32_rmt_issue_pulses(size_t n_args, const mp_obj_t *args) {
    esp32_rmt_obj_t *self = MP_OBJ_TO_PTR(args[0]);
    mp_obj_t *tx_ready_fn = MP_OBJ_TO_PTR(args[1]);
    mp_uint_t item_index = mp_obj_get_int(args[2]);
    mp_uint_t item_count = mp_obj_get_int(args[3]);
    self->clock_div = mp_obj_get_int(args[4]);

    check_esp_err(rmt_set_clk_div(self->channel_id, self->clock_div));
    
    rmt_register_tx_end_callback(esp32_rmt_private_tx_end_callback, tx_ready_fn);
    
    check_esp_err(rmt_write_items(self->channel_id, self->items + item_index, item_count, false));
    
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(esp32_rmt_issue_pulses_obj, 5, 5, esp32_rmt_issue_pulses);

// USER

STATIC mp_obj_t esp32_rmt_bitstream_channel(size_t n_args, const mp_obj_t *args) {
    if (n_args > 0) {
        if (args[0] == mp_const_none) {
            esp32_rmt_bitstream_channel_id = -1;
        } else {
            mp_int_t channel_id = mp_obj_get_int(args[0]);
            if (channel_id < 0 || channel_id > RMT_LAST_TX_CHANNEL) {
                mp_raise_ValueError(MP_ERROR_TEXT("invalid channel"));
            }
            esp32_rmt_bitstream_channel_id = channel_id;
        }
    }
    if (esp32_rmt_bitstream_channel_id < 0) {
        return mp_const_none;
    } else {
        return MP_OBJ_NEW_SMALL_INT(esp32_rmt_bitstream_channel_id);
    }
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(esp32_rmt_bitstream_channel_fun_obj, 0, 1, esp32_rmt_bitstream_channel);
STATIC MP_DEFINE_CONST_STATICMETHOD_OBJ(esp32_rmt_bitstream_channel_obj, MP_ROM_PTR(&esp32_rmt_bitstream_channel_fun_obj));

STATIC const mp_rom_map_elem_t esp32_rmt_locals_dict_table[] = {
    { MP_ROM_QSTR(MP_QSTR___del__), MP_ROM_PTR(&esp32_rmt_deinit_obj) },
    { MP_ROM_QSTR(MP_QSTR_deinit), MP_ROM_PTR(&esp32_rmt_deinit_obj) },
    { MP_ROM_QSTR(MP_QSTR_source_freq), MP_ROM_PTR(&esp32_rmt_source_freq_obj) },
    { MP_ROM_QSTR(MP_QSTR_clock_div), MP_ROM_PTR(&esp32_rmt_clock_div_obj) },
    { MP_ROM_QSTR(MP_QSTR_wait_done), MP_ROM_PTR(&esp32_rmt_wait_done_obj) },
    { MP_ROM_QSTR(MP_QSTR_loop), MP_ROM_PTR(&esp32_rmt_loop_obj) },
    { MP_ROM_QSTR(MP_QSTR_write_pulses), MP_ROM_PTR(&esp32_rmt_write_pulses_obj) },

    // USER
    { MP_ROM_QSTR(MP_QSTR_store_pulses), MP_ROM_PTR(&esp32_rmt_store_pulses_obj) },
    { MP_ROM_QSTR(MP_QSTR_issue_pulses), MP_ROM_PTR(&esp32_rmt_issue_pulses_obj) },
    // USER

    // Static methods
    { MP_ROM_QSTR(MP_QSTR_bitstream_channel), MP_ROM_PTR(&esp32_rmt_bitstream_channel_obj) },
};
STATIC MP_DEFINE_CONST_DICT(esp32_rmt_locals_dict, esp32_rmt_locals_dict_table);

const mp_obj_type_t esp32_rmt_type = {
    { &mp_type_type },
    .name = MP_QSTR_RMT,
    .print = esp32_rmt_print,
    .make_new = esp32_rmt_make_new,
    .locals_dict = (mp_obj_dict_t *)&esp32_rmt_locals_dict,
};

planner.py

"""
servo-like motion planner for nema-based stepper driver
"""

import micropython

# stepper driver mciro-command headers
PLAN_CMD_RAMP = micropython.const(577)  # send ramp pulses
PLAN_CMD_STOP = micropython.const(701)  # terminate program

#
# note: rmt_item32_t format (esp32 is little endian)
# https://github.com/espressif/esp-idf/blob/master/components/driver/include/driver/rmt.h
# https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/rmt.html
#
# typedef struct {
#     union {
#         struct {
#             uint32_t duration0 : 15; /*!< Duration of level0 */
#             uint32_t level0 : 1;     /*!< Level of the first part */
#             uint32_t duration1 : 15; /*!< Duration of level1 */
#             uint32_t level1 : 1;     /*!< Level of the second part */
#         };
#         uint32_t val; /*!< Equivelent unsigned value for the RMT item */
#     };
# } rmt_item32_t;


# define single stepper driver pulse as rmt_item32_t entry
# pulse_head -> "rmt first part duration", pulse_tail -> "rmt second part duration"
@micropython.viper  # @UndefinedVariable
def make_rmt_item32(pulse_head:int, pulse_tail:int) -> int:
    level_head = 1
    level_tail = 0
    return ((level_head << 15 | pulse_head) << 0) | ((level_tail << 15 | pulse_tail) << 16)


# convert stepper pulses into rmt items
def make_rmt_item_list(head_size:int, period_list:list[int]) -> list["rmt_item32"]:
    item_list = []
    for period in period_list:
        pulse_head = head_size
        pulse_tail = period - head_size
        rmt_item32 = make_rmt_item32(pulse_head, pulse_tail)
        item_list.append(rmt_item32)
    return item_list


class Planner:
    """
    servo-like motion planner for nema-based stepper driver
    """

    def __init__(self,
        motor_steps:int=200,  # motor steps per turn, count
        motor_gear:int=22,  # motion source or motor teeth, count
        drive_gear:int=85,  # motion target or drive teeth, count
        drive_freq_zero:float=0.4,  # "zero" mode, or drive start up speed, Hz
        drive_freq_slow:float=2.0,  # "slow" mode drive steady rotation speed, Hz
        drive_freq_fast:float=10.0,  # "fast" mode drive steady rotation speed, Hz
        pulse_size_min:int=40,  # stepper driver pulse limit, micro sec
        turn_block_count:int=8,  # number of ramp blocks in one drive turn, count of block
        clock_rate:int=80,  # esp32.RMT driver base clock, MHz
        clock_div_min:int=10,  # rmt clock divider range limit, count
        clock_div_max:int=250,  # rmt clock divider range limit, count
        ):

        self.motor_steps = motor_steps  # motor steps per one motor turn
        self.drive_steps = motor_steps * drive_gear / motor_gear  # motor steps per one drive turn
        self.drive_freq_zero = drive_freq_zero
        self.drive_freq_slow = drive_freq_slow
        self.drive_freq_fast = drive_freq_fast
        self.clock_div_min = clock_div_min
        self.clock_div_max = clock_div_max
        self.pulse_size_min = pulse_size_min
        self.turn_block_count = turn_block_count
        self.ramp_block_size_raw = self.drive_steps / turn_block_count
        self.ramp_block_size_int = round(self.ramp_block_size_raw)  # number of pulses in a ramp, count of item

        self.clock_rate = clock_rate
        clock_time_min = clock_div_min / self.clock_rate  # minimal planner time unit, micro sec
        clock_time_max = clock_div_max / self.clock_rate  # maximal planner time unit, micro sec
        # print(f"{clock_time_min=} {clock_time_max=}")

        assert drive_freq_fast < 20  # mechanical limits
        assert drive_freq_zero > 0.1  # mechanical limits
        assert drive_freq_fast > drive_freq_slow
        assert drive_freq_slow > drive_freq_zero

        period_base = 1e6 / self.drive_steps
        period_zero = period_base / drive_freq_zero  # micro sec
        period_slow = period_base / drive_freq_slow  # micro sec

        self.turn_unit_ratio = period_slow / period_zero  # speed ratio for single drive turn
        self.ramp_unit_ratio = self.turn_unit_ratio ** (1 / turn_block_count)  # for single ramp block
        # print(f"{self.turn_unit_ratio=:.4f} {self.ramp_unit_ratio=:.4f}")

        self.ramp_unit_max = period_zero / clock_time_max  # maximum number of rmt items in one pulse
        self.ramp_unit_min = self.ramp_unit_max * self.ramp_unit_ratio  # minimum  number of rmt items in one pulse
        # print(f"{self.ramp_unit_max=:.2f} {self.ramp_unit_min=:.2f}")

        self.ramp_unit_delta = (self.ramp_unit_max - self.ramp_unit_min) / self.ramp_block_size_int  # rmt item change rate
        # print(f"{self.ramp_block_size_int=:.2f} {self.ramp_unit_delta=:.2f}")

        # rmt item list offsets for the item ramps
        self.index_increase = self.ramp_block_size_int * 0
        self.index_constant = self.ramp_block_size_int * 1
        self.index_decrease = self.ramp_block_size_int * 2
        self.item_list_size = self.ramp_block_size_int * 3  # using only 3 ramps

        self.this_step_count_int = 0  # remember discrete drive step count
        self.this_step_count_raw = 0.0  # remember exact drive step count

        self.this_drive_freq = drive_freq_zero  # remember current drive rotation speed, Hz

    @property
    def current_drive_freq(self) -> float:
        return self.this_drive_freq

    @property
    def current_stepper_error(self) -> float:
        return self.this_step_count_int - self.this_step_count_raw

    def make_item_list(self) -> list["rmt_item32"]:
        """
        generate rmt item list stored inside rmt driver esp32.RMT
        """
        period_list = self.make_period_list()
        head_size = round(self.ramp_unit_min / 2)  # split pulse into "head" and "tail" in the middle
        item_list = make_rmt_item_list(head_size, period_list)  # generate rmt item list
        assert len(item_list) == self.item_list_size  # ensure total rapms collection
        return item_list

    def make_period_list(self) -> list[int]:
        """
        generate stepper pulse list stitched from pulse blocks: increase, constant, decrease
        """
        ramp_decrease = [  # generate speed "decrease"
            round(self.ramp_unit_min + index * self.ramp_unit_delta)
            for index in range(self.ramp_block_size_int)
        ]
        ramp_increase = [  # generate speed "increase"
            round(self.ramp_unit_max - index * self.ramp_unit_delta - self.ramp_unit_delta)
            for index in range(self.ramp_block_size_int)
        ]
        ramp_constant = self.ramp_block_size_int * [round(self.ramp_unit_min)]  # generate speed "coasting" sequence

        # print(f"ramp_decrease head:{ramp_decrease[:+10]} tail:{ramp_decrease[-10:]}")
        # print(f"ramp_increase head:{ramp_increase[:+10]} tail:{ramp_increase[-10:]}")
        # print(f"ramp_constant head:{ramp_constant[:+10]} tail:{ramp_constant[-10:]}")
        assert ramp_increase[-1] == ramp_constant[+0]  # ensure ramp stitch level
        assert ramp_constant[+0] == ramp_constant[-1]  # ensure ramp stitch level
        assert ramp_constant[-1] == ramp_decrease[+0]  # ensure ramp stitch level

        period_list = ramp_increase + ramp_constant + ramp_decrease  # keep ramps in order
        assert len(period_list) == self.item_list_size  # ensure total rapms collection
        assert all(
            period > self.pulse_size_min  # stepper drive pulse limit
            and period < 32768  # rmt item duration is in 15-bit range
            for period in period_list
        )

        return period_list

    def make_plan_rotate(self,
            freq_mode:int,  # speed change mode: -1, 0, +1
            drive_turn:float,  # number of drive turns
        ) -> list[int]:
        """
        generate stepper motion micro-program, executed by stepper driver
        """

        # print(f"{self.this_drive_freq=:.2f}")

        freq_past = self.this_drive_freq  # drive frequency at the beginning of this motion

        freq_zero = self.drive_freq_zero  # TODO ensure limits
        freq_slow = self.drive_freq_slow  # TODO ensure limits
        freq_fast = self.drive_freq_fast  # TODO ensure limits

        if freq_mode == 0:  # continue
            freq_ratio = 1
            index_base = self.index_constant
            unit_base = self.ramp_unit_min
        elif freq_mode < 0:  # decelerate
            freq_ratio = 1 * self.ramp_unit_ratio
            index_base = self.index_decrease
            unit_base = self.ramp_unit_min
        elif freq_mode > 0:  # accelerate
            freq_ratio = 1 / self.ramp_unit_ratio
            index_base = self.index_increase
            unit_base = self.ramp_unit_max
        else:
            assert False

        plan_rotate = []  # stepper command list
        clock_rate = self.clock_rate
        drive_steps = self.drive_steps
        period_base = 1e6 / drive_steps
        block_size_int = self.ramp_block_size_int
        block_size_raw = self.ramp_block_size_raw
        ramp_count = round(drive_turn * self.turn_block_count)

        for ramp_index in range(ramp_count):
            # correct for discretization error
            self.this_step_count_int += block_size_int
            self.this_step_count_raw += block_size_raw
            block_step_error = round(self.current_stepper_error)
            self.this_step_count_int -= block_step_error
            # produce ramp motion parameters
            freq_next = freq_past * (freq_ratio ** ramp_index)
            period_next = period_base / freq_next
            clock_time = period_next / unit_base
            clock_div = round(clock_rate * clock_time)
            # generate motion micro-instruction
            item_start = index_base
            item_count = block_size_int - block_step_error
            plan_block = [PLAN_CMD_RAMP, item_start, item_count, clock_div]  # single stepper command
            plan_rotate += plan_block
            # print(f"{freq_next=:.2f} {clock_time=:.2f} {clock_div=}")

        self.this_drive_freq = freq_past * (freq_ratio ** ramp_count)  # drive frequency at the end of this motion

        # print(f"{self.this_drive_freq=:.2f}")

        return plan_rotate

ringer.py

"""
isr-safe ring buffer
"""

import array
import micropython


class Ringer:
    """
    note: use isr rules https://docs.micropython.org/en/latest/reference/isr_rules.html
    """

    def __init__(self,
        ring_power:int=6,  # base 2 log of ring size
        ring_type:object="H",  # unsigned short
        ):
        self.ring_power:int = ring_power
        self.ring_size:int = 1 << ring_power
        self.ring_mask:int = self.ring_size - 1
        self.index_get:int = 0
        self.index_put:int = 0
        self.ring_data = array.array(ring_type, (0 for _ in range(self.ring_size)))

    @micropython.native  # @UndefinedVariable
    def ring_get(self) -> int:
        past_index_get = self.index_get
        next_index_get = (past_index_get + 1) & self.ring_mask
        if past_index_get == self.index_put:
            return None  # ring is empty
        else:
            value = self.ring_data[past_index_get]
            self.index_get = next_index_get
            return value

    @micropython.native  # @UndefinedVariable
    def ring_put(self, value:int) -> int:
        past_index_put = self.index_put
        next_index_put = (past_index_put + 1) & self.ring_mask
        if next_index_put == self.index_get:
            return None  # ring is full
        else:
            self.ring_data[past_index_put] = value
            self.index_put = next_index_put
            return value

stepper.py

"""
servo-like nema-based stepper driver based on esp32.RMT driver
"""
#
# https://github.com/micropython/micropython/issues/7015
# https://docs.micropython.org/en/latest/library/esp32.html
# https://forum.micropython.org/viewtopic.php?f=15&t=7497&start=30#p61390
#

import esp32
import micropython

from utime import sleep_us
from uasyncio import ThreadSafeFlag

from machine import Pin
from ringer import Ringer
from planner import Planner
from planner import PLAN_CMD_RAMP
from planner import PLAN_CMD_STOP


class Stepper:

    def __init__(self,
        pin_en:int,  # stepper driver pin; "enalbe"
        pin_dir:int,  # stepper driver pin: "direction"
        pin_step:int,  # stepper driver pin: "make a step"
        ringer:Ringer,  # micro-program ring buffer
        planner:Planner,  # servo-like motion planner
        rmt_channel:int=0,  # rmt driver to stepper binding
        invert_enable:bool=False,  # init with "OFF"
        invert_direction:bool=False,  # init with "CCW"
        delay_enable_us:int=10,  # stepper driver conditioning
        delay_direction_us:int=5,  # stepper driver conditioning
        ):

        self.pin_en = Pin(pin_en, mode=Pin.OUT, value=int(invert_enable))
        self.pin_dir = Pin(pin_dir, mode=Pin.OUT, value=int(invert_direction))
        self.pin_step = Pin(pin_step, mode=Pin.OUT, value=0)

        self.invert_enable = invert_enable
        self.invert_direction = invert_direction
        self.delay_enable_us = delay_enable_us
        self.delay_direction_us = delay_direction_us

        self.ringer = ringer
        self.planner = planner

        self.event_cmd_ramp = ThreadSafeFlag()  # motion ramp start event
        self.event_cmd_stop = ThreadSafeFlag()  # motion program finish event
        self.event_cmd_trap = ThreadSafeFlag()  # motion program error detector

        self.transmit_function = self.transmit_reactor  # fun-ref to avoid memory allocation inside isr

        self.rmt_driver = esp32.RMT(
            id=rmt_channel,
            pin=self.pin_step,
            # source_freq=80_000_000,  # fixed in driver
            clock_div=80,  # 1 micro second time unit
            idle_level=0,  # initial signal level
            tx_carrier=None,  # do not chop signal
        )
        self.rmt_driver.loop(False)  # actually: enable interrupt for "transmit ready" isr
        self.rmt_driver.store_pulses(self.planner.make_item_list())  # persist ramp block patterns

    async def await_cmd_ramp(self) -> None:
        await self.event_cmd_ramp.wait()

    async def await_cmd_stop(self) -> None:
        await self.event_cmd_stop.wait()

    async def await_cmd_trap(self) -> None:
        await self.event_cmd_trap.wait()

    def make_enable(self, on:bool) -> None:
        self.pin_en.value(int(on ^ self.invert_enable))
        sleep_us(self.delay_enable_us)

    def make_direction(self, on:bool) -> None:
        self.pin_dir.value(int(on ^ self.invert_direction))
        sleep_us(self.delay_direction_us)

    def persist_motion_plan(self, plan_rotate:list[int]) -> None:
        "populate ring buffer with micro commands"
        for value in plan_rotate:
            result = self.ringer.ring_put(value)
            assert result is not None  # buffer not full

    def make_rotation_one(self) -> None:
        "accelerate then decelerate during single drive turn"
        plan_one = self.planner.make_plan_rotate(+1, 0.5)
        plan_two = self.planner.make_plan_rotate(-1, 0.5)
        plan_full = plan_one + plan_two + [PLAN_CMD_STOP]
        # print(f"{plan_full=}")
        self.persist_motion_plan(plan_full)
        self.transmit_reactor()  # start transmit with isr self call

    def make_rotation_start(self) -> None:
        pass  # TODO

    def make_rotation_finish(self) -> None:
        pass  # TODO

    @micropython.native  # @UndefinedVariable
    def transmit_reactor(self):
        """
        function to execute stepper micro-program:
        * invoked by self "make rotation" methods for motion start
        * invoked by esp32.RMT driver "transmit ready" ISR to continue motion
        note: use isr rules https://docs.micropython.org/en/latest/reference/isr_rules.html
        """
        buffer = self.ringer
        header = buffer.ring_get()  # micro-command prefix

        if header == PLAN_CMD_RAMP:
            # micro-command parameters
            item_index = buffer.ring_get()
            item_count = buffer.ring_get()
            clock_div = buffer.ring_get()
            # start pulse sequence form rmt driver store
            self.rmt_driver.issue_pulses(# non blocking invocation
                self.transmit_function,  # this is isr setup to self
                item_index,  # place in the store
                item_count,  # pulse ramp block size
                clock_div,  # frequency for this block
            )
            self.event_cmd_ramp.set()
            return

        if header == PLAN_CMD_STOP:
            self.event_cmd_stop.set()
            return

        self.event_cmd_trap.set()  # should not happen