micropython/cc3200/mods/pybtimer.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2013, 2014 Damien P. George
 * Copyright (c) 2015 Daniel Campora
 *
 * 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 <stdint.h>
#include <stdio.h>
#include <string.h>

#include "py/mpconfig.h"
#include "py/obj.h"
#include "py/nlr.h"
#include "py/runtime.h"
#include "py/gc.h"
#include "py/mperrno.h"
#include "py/mphal.h"
#include "inc/hw_types.h"
#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "inc/hw_timer.h"
#include "rom_map.h"
#include "interrupt.h"
#include "prcm.h"
#include "timer.h"
#include "pin.h"
#include "pybtimer.h"
#include "pybpin.h"
#include "pins.h"
#include "mpirq.h"
#include "pybsleep.h"
#include "mpexception.h"


/// \moduleref pyb
/// \class Timer - generate periodic events, count events, and create PWM signals.
///
/// Each timer consists of a counter that counts up at a certain rate.  The rate
/// at which it counts is the peripheral clock frequency (in Hz) divided by the
/// timer prescaler.  When the counter reaches the timer period it triggers an
/// event, and the counter resets back to zero.  By using the irq method,
/// the timer event can call a Python function.

/******************************************************************************
 DECLARE PRIVATE CONSTANTS
 ******************************************************************************/
#define PYBTIMER_NUM_TIMERS                         (4)
#define PYBTIMER_POLARITY_POS                       (0x01)
#define PYBTIMER_POLARITY_NEG                       (0x02)

#define PYBTIMER_TIMEOUT_TRIGGER                    (0x01)
#define PYBTIMER_MATCH_TRIGGER                      (0x02)

#define PYBTIMER_SRC_FREQ_HZ                        HAL_FCPU_HZ

/******************************************************************************
 DEFINE PRIVATE TYPES
 ******************************************************************************/
typedef struct _pyb_timer_obj_t {
    mp_obj_base_t base;
    uint32_t timer;
    uint32_t config;
    uint16_t irq_trigger;
    uint16_t irq_flags;
    uint8_t peripheral;
    uint8_t id;
} pyb_timer_obj_t;

typedef struct _pyb_timer_channel_obj_t {
    mp_obj_base_t base;
    struct _pyb_timer_obj_t *timer;
    uint32_t frequency;
    uint32_t period;
    uint16_t channel;
    uint16_t duty_cycle;
    uint8_t  polarity;
} pyb_timer_channel_obj_t;

/******************************************************************************
 DEFINE PRIVATE DATA
 ******************************************************************************/
STATIC const mp_irq_methods_t pyb_timer_channel_irq_methods;
STATIC pyb_timer_obj_t pyb_timer_obj[PYBTIMER_NUM_TIMERS] = {{.timer = TIMERA0_BASE, .peripheral = PRCM_TIMERA0},
                                                             {.timer = TIMERA1_BASE, .peripheral = PRCM_TIMERA1},
                                                             {.timer = TIMERA2_BASE, .peripheral = PRCM_TIMERA2},
                                                             {.timer = TIMERA3_BASE, .peripheral = PRCM_TIMERA3}};
STATIC const mp_obj_type_t pyb_timer_channel_type;
STATIC const mp_obj_t pyb_timer_pwm_pin[8] = {&pin_GP24, MP_OBJ_NULL, &pin_GP25, MP_OBJ_NULL, MP_OBJ_NULL, &pin_GP9, &pin_GP10, &pin_GP11};

/******************************************************************************
 DECLARE PRIVATE FUNCTIONS
 ******************************************************************************/
STATIC mp_obj_t pyb_timer_channel_irq (mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args);
STATIC void timer_disable (pyb_timer_obj_t *tim);
STATIC void timer_channel_init (pyb_timer_channel_obj_t *ch);
STATIC void TIMER0AIntHandler(void);
STATIC void TIMER0BIntHandler(void);
STATIC void TIMER1AIntHandler(void);
STATIC void TIMER1BIntHandler(void);
STATIC void TIMER2AIntHandler(void);
STATIC void TIMER2BIntHandler(void);
STATIC void TIMER3AIntHandler(void);
STATIC void TIMER3BIntHandler(void);

/******************************************************************************
 DEFINE PUBLIC FUNCTIONS
 ******************************************************************************/
void timer_init0 (void) {
    mp_obj_list_init(&MP_STATE_PORT(pyb_timer_channel_obj_list), 0);
}

/******************************************************************************
 DEFINE PRIVATE FUNCTIONS
 ******************************************************************************/
STATIC void pyb_timer_channel_irq_enable (mp_obj_t self_in) {
    pyb_timer_channel_obj_t *self = self_in;
    MAP_TimerIntClear(self->timer->timer, self->timer->irq_trigger & self->channel);
    MAP_TimerIntEnable(self->timer->timer, self->timer->irq_trigger & self->channel);
}

STATIC void pyb_timer_channel_irq_disable (mp_obj_t self_in) {
    pyb_timer_channel_obj_t *self = self_in;
    MAP_TimerIntDisable(self->timer->timer, self->timer->irq_trigger & self->channel);
}

STATIC int pyb_timer_channel_irq_flags (mp_obj_t self_in) {
    pyb_timer_channel_obj_t *self = self_in;
    return self->timer->irq_flags;
}

STATIC pyb_timer_channel_obj_t *pyb_timer_channel_find (uint32_t timer, uint16_t channel_n) {
    for (mp_uint_t i = 0; i < MP_STATE_PORT(pyb_timer_channel_obj_list).len; i++) {
        pyb_timer_channel_obj_t *ch = ((pyb_timer_channel_obj_t *)(MP_STATE_PORT(pyb_timer_channel_obj_list).items[i]));
        // any 32-bit timer must be matched by any of its 16-bit versions
        if (ch->timer->timer == timer && ((ch->channel & TIMER_A) == channel_n || (ch->channel & TIMER_B) == channel_n)) {
            return ch;
        }
    }
    return MP_OBJ_NULL;
}

STATIC void pyb_timer_channel_remove (pyb_timer_channel_obj_t *ch) {
    pyb_timer_channel_obj_t *channel;
    if ((channel = pyb_timer_channel_find(ch->timer->timer, ch->channel))) {
        mp_obj_list_remove(&MP_STATE_PORT(pyb_timer_channel_obj_list), channel);
        // unregister it with the sleep module
        pyb_sleep_remove((const mp_obj_t)channel);
    }
}

STATIC void pyb_timer_channel_add (pyb_timer_channel_obj_t *ch) {
    // remove it in case it already exists
    pyb_timer_channel_remove(ch);
    mp_obj_list_append(&MP_STATE_PORT(pyb_timer_channel_obj_list), ch);
    // register it with the sleep module
    pyb_sleep_add((const mp_obj_t)ch, (WakeUpCB_t)timer_channel_init);
}

STATIC void timer_disable (pyb_timer_obj_t *tim) {
    // disable all timers and it's interrupts
    MAP_TimerDisable(tim->timer, TIMER_A | TIMER_B);
    MAP_TimerIntDisable(tim->timer, tim->irq_trigger);
    MAP_TimerIntClear(tim->timer, tim->irq_trigger);
    pyb_timer_channel_obj_t *ch;
    // disable its channels
    if ((ch = pyb_timer_channel_find (tim->timer, TIMER_A))) {
        pyb_sleep_remove(ch);
    }
    if ((ch = pyb_timer_channel_find (tim->timer, TIMER_B))) {
        pyb_sleep_remove(ch);
    }
    MAP_PRCMPeripheralClkDisable(tim->peripheral, PRCM_RUN_MODE_CLK | PRCM_SLP_MODE_CLK);
}

// computes prescaler period and match value so timer triggers at freq-Hz
STATIC uint32_t compute_prescaler_period_and_match_value(pyb_timer_channel_obj_t *ch, uint32_t *period_out, uint32_t *match_out) {
    uint32_t maxcount = (ch->channel == (TIMER_A | TIMER_B)) ? 0xFFFFFFFF : 0xFFFF;
    uint32_t prescaler;
    uint32_t period_c = (ch->frequency > 0) ? PYBTIMER_SRC_FREQ_HZ / ch->frequency : ((PYBTIMER_SRC_FREQ_HZ / 1000000) * ch->period);

    period_c = MAX(1, period_c) - 1;
    if (period_c == 0) {
        goto error;
    }

    prescaler = period_c >> 16; // The prescaler is an extension of the timer counter
    *period_out = period_c;

    if (prescaler > 0xFF && maxcount == 0xFFFF) {
        goto error;
    }
    // check limit values for the duty cycle
    if (ch->duty_cycle == 0) {
        *match_out = period_c - 1;
    } else {
        if (period_c > 0xFFFF) {
            uint32_t match = (period_c * 100) / 10000;
            *match_out = period_c - ((match * ch->duty_cycle) / 100);
        } else {
            *match_out = period_c - ((period_c * ch->duty_cycle) / 10000);
        }
    }
    return prescaler;

error:
    mp_raise_ValueError(mpexception_value_invalid_arguments);
}

STATIC void timer_init (pyb_timer_obj_t *tim) {
    MAP_PRCMPeripheralClkEnable(tim->peripheral, PRCM_RUN_MODE_CLK | PRCM_SLP_MODE_CLK);
    MAP_PRCMPeripheralReset(tim->peripheral);
    MAP_TimerConfigure(tim->timer, tim->config);
}

STATIC void timer_channel_init (pyb_timer_channel_obj_t *ch) {
    // calculate the period, the prescaler and the match value
    uint32_t period_c;
    uint32_t match;
    uint32_t prescaler = compute_prescaler_period_and_match_value(ch, &period_c, &match);

    // set the prescaler
    MAP_TimerPrescaleSet(ch->timer->timer, ch->channel, (prescaler < 0xFF) ? prescaler : 0);

    // set the load value
    MAP_TimerLoadSet(ch->timer->timer, ch->channel, period_c);

    // configure the pwm if we are in such mode
    if ((ch->timer->config & 0x0F) == TIMER_CFG_A_PWM) {
        // invert the timer output if required
        MAP_TimerControlLevel(ch->timer->timer, ch->channel, (ch->polarity == PYBTIMER_POLARITY_NEG) ? true : false);
        // set the match value (which is simply the duty cycle translated to ticks)
        MAP_TimerMatchSet(ch->timer->timer, ch->channel, match);
        MAP_TimerPrescaleMatchSet(ch->timer->timer, ch->channel, match >> 16);
    }

#ifdef DEBUG
    // stall the timer when the processor is halted while debugging
    MAP_TimerControlStall(ch->timer->timer, ch->channel, true);
#endif

    // now enable the timer channel
    MAP_TimerEnable(ch->timer->timer, ch->channel);
}

/******************************************************************************/
/* MicroPython bindings                                                      */

STATIC void pyb_timer_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
    pyb_timer_obj_t *tim = self_in;
    uint32_t mode = tim->config & 0xFF;

    // timer mode
    qstr mode_qst = MP_QSTR_PWM;
    switch(mode) {
    case TIMER_CFG_A_ONE_SHOT_UP:
        mode_qst = MP_QSTR_ONE_SHOT;
        break;
    case TIMER_CFG_A_PERIODIC_UP:
        mode_qst = MP_QSTR_PERIODIC;
        break;
    default:
        break;
    }
    mp_printf(print, "Timer(%u, mode=Timer.%q)", tim->id, mode_qst);
}

STATIC mp_obj_t pyb_timer_init_helper(pyb_timer_obj_t *tim, mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
    static const mp_arg_t allowed_args[] = {
        { MP_QSTR_mode,         MP_ARG_REQUIRED | MP_ARG_INT, },
        { MP_QSTR_width,        MP_ARG_KW_ONLY  | MP_ARG_INT, {.u_int = 16} },
    };

    // parse args
    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);

    // check the mode
    uint32_t _mode = args[0].u_int;
    if (_mode != TIMER_CFG_A_ONE_SHOT_UP && _mode != TIMER_CFG_A_PERIODIC_UP && _mode != TIMER_CFG_A_PWM) {
        goto error;
    }

    // check the width
    if (args[1].u_int != 16 && args[1].u_int != 32) {
        goto error;
    }
    bool is16bit = (args[1].u_int == 16);

    if (!is16bit && _mode == TIMER_CFG_A_PWM) {
        // 32-bit mode is only available when in free running modes
        goto error;
    }
    tim->config = is16bit ? ((_mode | (_mode << 8)) | TIMER_CFG_SPLIT_PAIR) : _mode;

    timer_init(tim);
    // register it with the sleep module
    pyb_sleep_add ((const mp_obj_t)tim, (WakeUpCB_t)timer_init);

    return mp_const_none;

error:
    mp_raise_ValueError(mpexception_value_invalid_arguments);
}

STATIC mp_obj_t pyb_timer_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
    // check arguments
    mp_arg_check_num(n_args, n_kw, 1, MP_OBJ_FUN_ARGS_MAX, true);

    // create a new Timer object
    int32_t timer_idx = mp_obj_get_int(args[0]);
    if (timer_idx < 0 || timer_idx > (PYBTIMER_NUM_TIMERS - 1)) {
        mp_raise_OSError(MP_ENODEV);
    }

    pyb_timer_obj_t *tim = &pyb_timer_obj[timer_idx];
    tim->base.type = &pyb_timer_type;
    tim->id = timer_idx;

    if (n_args > 1 || n_kw > 0) {
        // start the peripheral
        mp_map_t kw_args;
        mp_map_init_fixed_table(&kw_args, n_kw, args + n_args);
        pyb_timer_init_helper(tim, n_args - 1, args + 1, &kw_args);
    }
    return (mp_obj_t)tim;
}

STATIC mp_obj_t pyb_timer_init(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
    return pyb_timer_init_helper(args[0], n_args - 1, args + 1, kw_args);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_timer_init_obj, 1, pyb_timer_init);

STATIC mp_obj_t pyb_timer_deinit(mp_obj_t self_in) {
    pyb_timer_obj_t *self = self_in;
    timer_disable(self);
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_timer_deinit_obj, pyb_timer_deinit);

STATIC mp_obj_t pyb_timer_channel(mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
    static const mp_arg_t allowed_args[] = {
        { MP_QSTR_freq,                MP_ARG_KW_ONLY  | MP_ARG_INT, {.u_int = 0} },
        { MP_QSTR_period,              MP_ARG_KW_ONLY  | MP_ARG_INT, {.u_int = 0} },
        { MP_QSTR_polarity,            MP_ARG_KW_ONLY  | MP_ARG_INT, {.u_int = PYBTIMER_POLARITY_POS} },
        { MP_QSTR_duty_cycle,          MP_ARG_KW_ONLY  | MP_ARG_INT, {.u_int = 0} },
    };

    pyb_timer_obj_t *tim = pos_args[0];
    mp_int_t channel_n = mp_obj_get_int(pos_args[1]);

    // verify that the timer has been already initialized
    if (!tim->config) {
        mp_raise_OSError(MP_EPERM);
    }
    if (channel_n != TIMER_A && channel_n != TIMER_B && channel_n != (TIMER_A | TIMER_B)) {
        // invalid channel
        goto error;
    }
    if (channel_n == (TIMER_A | TIMER_B) && (tim->config & TIMER_CFG_SPLIT_PAIR)) {
        // 32-bit channel selected when the timer is in 16-bit mode
        goto error;
    }

    // if only the channel number is given return the previously
    // allocated channel (or None if no previous channel)
    if (n_args == 2 && kw_args->used == 0) {
        pyb_timer_channel_obj_t *ch;
        if ((ch = pyb_timer_channel_find(tim->timer, channel_n))) {
            return ch;
        }
        return mp_const_none;
    }

    // parse the arguments
    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
    mp_arg_parse_all(n_args - 2, pos_args + 2, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);

    // throw an exception if both frequency and period are given
    if (args[0].u_int != 0 && args[1].u_int != 0) {
        goto error;
    }
    // check that at least one of them has a valid value
    if (args[0].u_int <= 0 && args[1].u_int <= 0) {
        goto error;
    }
    // check that the polarity is not 'both' in pwm mode
    if ((tim->config & TIMER_A) == TIMER_CFG_A_PWM && args[2].u_int == (PYBTIMER_POLARITY_POS | PYBTIMER_POLARITY_NEG)) {
        goto error;
    }

    // allocate a new timer channel
    pyb_timer_channel_obj_t *ch = m_new_obj(pyb_timer_channel_obj_t);
    ch->base.type = &pyb_timer_channel_type;
    ch->timer = tim;
    ch->channel = channel_n;

    // get the frequency the polarity and the duty cycle
    ch->frequency = args[0].u_int;
    ch->period = args[1].u_int;
    ch->polarity = args[2].u_int;
    ch->duty_cycle = MIN(10000, MAX(0, args[3].u_int));

    timer_channel_init(ch);

    // assign the pin
    if ((ch->timer->config & 0x0F) == TIMER_CFG_A_PWM) {
        uint32_t ch_idx = (ch->channel == TIMER_A) ? 0 : 1;
        // use the default pin if available
        mp_obj_t pin_o = (mp_obj_t)pyb_timer_pwm_pin[(ch->timer->id * 2) + ch_idx];
        if (pin_o != MP_OBJ_NULL) {
            pin_obj_t *pin = pin_find(pin_o);
            pin_config (pin, pin_find_af_index(pin, PIN_FN_TIM, ch->timer->id, PIN_TYPE_TIM_PWM),
                        0, PIN_TYPE_STD, -1, PIN_STRENGTH_4MA);
        }
    }

    // add the timer to the list
    pyb_timer_channel_add(ch);

    return ch;

error:
    mp_raise_ValueError(mpexception_value_invalid_arguments);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_timer_channel_obj, 2, pyb_timer_channel);

STATIC const mp_rom_map_elem_t pyb_timer_locals_dict_table[] = {
    // instance methods
    { MP_ROM_QSTR(MP_QSTR_init),                    MP_ROM_PTR(&pyb_timer_init_obj) },
    { MP_ROM_QSTR(MP_QSTR_deinit),                  MP_ROM_PTR(&pyb_timer_deinit_obj) },
    { MP_ROM_QSTR(MP_QSTR_channel),                 MP_ROM_PTR(&pyb_timer_channel_obj) },

    // class constants
    { MP_ROM_QSTR(MP_QSTR_A),                       MP_ROM_INT(TIMER_A) },
    { MP_ROM_QSTR(MP_QSTR_B),                       MP_ROM_INT(TIMER_B) },
    { MP_ROM_QSTR(MP_QSTR_ONE_SHOT),                MP_ROM_INT(TIMER_CFG_A_ONE_SHOT_UP) },
    { MP_ROM_QSTR(MP_QSTR_PERIODIC),                MP_ROM_INT(TIMER_CFG_A_PERIODIC_UP) },
    { MP_ROM_QSTR(MP_QSTR_PWM),                     MP_ROM_INT(TIMER_CFG_A_PWM) },
    { MP_ROM_QSTR(MP_QSTR_POSITIVE),                MP_ROM_INT(PYBTIMER_POLARITY_POS) },
    { MP_ROM_QSTR(MP_QSTR_NEGATIVE),                MP_ROM_INT(PYBTIMER_POLARITY_NEG) },
    { MP_ROM_QSTR(MP_QSTR_TIMEOUT),                 MP_ROM_INT(PYBTIMER_TIMEOUT_TRIGGER) },
    { MP_ROM_QSTR(MP_QSTR_MATCH),                   MP_ROM_INT(PYBTIMER_MATCH_TRIGGER) },
};
STATIC MP_DEFINE_CONST_DICT(pyb_timer_locals_dict, pyb_timer_locals_dict_table);

const mp_obj_type_t pyb_timer_type = {
    { &mp_type_type },
    .name = MP_QSTR_Timer,
    .print = pyb_timer_print,
    .make_new = pyb_timer_make_new,
    .locals_dict = (mp_obj_t)&pyb_timer_locals_dict,
};

STATIC const mp_irq_methods_t pyb_timer_channel_irq_methods = {
    .init = pyb_timer_channel_irq,
    .enable = pyb_timer_channel_irq_enable,
    .disable = pyb_timer_channel_irq_disable,
    .flags = pyb_timer_channel_irq_flags,
};

STATIC void TIMERGenericIntHandler(uint32_t timer, uint16_t channel) {
    pyb_timer_channel_obj_t *self;
    uint32_t status;
    if ((self = pyb_timer_channel_find(timer, channel))) {
        status = MAP_TimerIntStatus(self->timer->timer, true) & self->channel;
        MAP_TimerIntClear(self->timer->timer, status);
        mp_irq_handler(mp_irq_find(self));
    }
}

STATIC void TIMER0AIntHandler(void) {
    TIMERGenericIntHandler(TIMERA0_BASE, TIMER_A);
}

STATIC void TIMER0BIntHandler(void) {
    TIMERGenericIntHandler(TIMERA0_BASE, TIMER_B);
}

STATIC void TIMER1AIntHandler(void) {
    TIMERGenericIntHandler(TIMERA1_BASE, TIMER_A);
}

STATIC void TIMER1BIntHandler(void) {
    TIMERGenericIntHandler(TIMERA1_BASE, TIMER_B);
}

STATIC void TIMER2AIntHandler(void) {
    TIMERGenericIntHandler(TIMERA2_BASE, TIMER_A);
}

STATIC void TIMER2BIntHandler(void) {
    TIMERGenericIntHandler(TIMERA2_BASE, TIMER_B);
}

STATIC void TIMER3AIntHandler(void) {
    TIMERGenericIntHandler(TIMERA3_BASE, TIMER_A);
}

STATIC void TIMER3BIntHandler(void) {
    TIMERGenericIntHandler(TIMERA3_BASE, TIMER_B);
}

STATIC void pyb_timer_channel_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
    pyb_timer_channel_obj_t *ch = self_in;
    char *ch_id = "AB";
    // timer channel
    if (ch->channel == TIMER_A) {
        ch_id = "A";
    } else if (ch->channel == TIMER_B) {
        ch_id = "B";
    }

    mp_printf(print, "timer.channel(Timer.%s, %q=%u", ch_id, MP_QSTR_freq, ch->frequency);

    uint32_t mode = ch->timer->config & 0xFF;
    if (mode == TIMER_CFG_A_PWM) {
        mp_printf(print, ", %q=Timer.", MP_QSTR_polarity);
        switch (ch->polarity) {
            case PYBTIMER_POLARITY_POS:
                mp_printf(print, "POSITIVE");
                break;
            case PYBTIMER_POLARITY_NEG:
                mp_printf(print, "NEGATIVE");
                break;
            default:
                mp_printf(print, "BOTH");
                break;
        }
        mp_printf(print, ", %q=%u.%02u", MP_QSTR_duty_cycle, ch->duty_cycle / 100, ch->duty_cycle % 100);
    }
    mp_printf(print, ")");
}

STATIC mp_obj_t pyb_timer_channel_freq(mp_uint_t n_args, const mp_obj_t *args) {
    pyb_timer_channel_obj_t *ch = args[0];
    if (n_args == 1) {
        // get
        return mp_obj_new_int(ch->frequency);
    } else {
        // set
        int32_t _frequency = mp_obj_get_int(args[1]);
        if (_frequency <= 0) {
            mp_raise_ValueError(mpexception_value_invalid_arguments);
        }
        ch->frequency = _frequency;
        ch->period = 1000000 / _frequency;
        timer_channel_init(ch);
        return mp_const_none;
    }
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(pyb_timer_channel_freq_obj, 1, 2, pyb_timer_channel_freq);

STATIC mp_obj_t pyb_timer_channel_period(mp_uint_t n_args, const mp_obj_t *args) {
    pyb_timer_channel_obj_t *ch = args[0];
    if (n_args == 1) {
        // get
        return mp_obj_new_int(ch->period);
    } else {
        // set
        int32_t _period = mp_obj_get_int(args[1]);
        if (_period <= 0) {
            mp_raise_ValueError(mpexception_value_invalid_arguments);
        }
        ch->period = _period;
        ch->frequency = 1000000 / _period;
        timer_channel_init(ch);
        return mp_const_none;
    }
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(pyb_timer_channel_period_obj, 1, 2, pyb_timer_channel_period);

STATIC mp_obj_t pyb_timer_channel_duty_cycle(mp_uint_t n_args, const mp_obj_t *args) {
    pyb_timer_channel_obj_t *ch = args[0];
    if (n_args == 1) {
        // get
        return mp_obj_new_int(ch->duty_cycle);
    } else {
        // duty cycle must be converted from percentage to ticks
        // calculate the period, the prescaler and the match value
        uint32_t period_c;
        uint32_t match;
        ch->duty_cycle = MIN(10000, MAX(0, mp_obj_get_int(args[1])));
        compute_prescaler_period_and_match_value(ch, &period_c, &match);
        if (n_args == 3) {
            // set the new polarity if requested
            ch->polarity = mp_obj_get_int(args[2]);
            MAP_TimerControlLevel(ch->timer->timer, ch->channel, (ch->polarity == PYBTIMER_POLARITY_NEG) ? true : false);
        }
        MAP_TimerMatchSet(ch->timer->timer, ch->channel, match);
        MAP_TimerPrescaleMatchSet(ch->timer->timer, ch->channel, match >> 16);
        return mp_const_none;
    }
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(pyb_timer_channel_duty_cycle_obj, 1, 3, pyb_timer_channel_duty_cycle);

STATIC mp_obj_t pyb_timer_channel_irq (mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
    mp_arg_val_t args[mp_irq_INIT_NUM_ARGS];
    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, mp_irq_INIT_NUM_ARGS, mp_irq_init_args, args);
    pyb_timer_channel_obj_t *ch = pos_args[0];

    // convert the priority to the correct value
    uint priority = mp_irq_translate_priority (args[1].u_int);

    // validate the power mode
    uint8_t pwrmode = (args[3].u_obj == mp_const_none) ? PYB_PWR_MODE_ACTIVE : mp_obj_get_int(args[3].u_obj);
    if (pwrmode != PYB_PWR_MODE_ACTIVE) {
        goto invalid_args;
    }

    // get the trigger
    uint trigger = mp_obj_get_int(args[0].u_obj);

    // disable the callback first
    pyb_timer_channel_irq_disable(ch);

    uint8_t shift = (ch->channel == TIMER_B) ? 8 : 0;
    uint32_t _config = (ch->channel == TIMER_B) ? ((ch->timer->config & TIMER_B) >> 8) : (ch->timer->config & TIMER_A);
    switch (_config) {
    case TIMER_CFG_A_ONE_SHOT_UP:
    case TIMER_CFG_A_PERIODIC_UP:
        ch->timer->irq_trigger |= TIMER_TIMA_TIMEOUT << shift;
        if (trigger != PYBTIMER_TIMEOUT_TRIGGER) {
            goto invalid_args;
        }
        break;
    case TIMER_CFG_A_PWM:
        // special case for the PWM match interrupt
        ch->timer->irq_trigger |= ((ch->channel & TIMER_A) == TIMER_A) ? TIMER_TIMA_MATCH : TIMER_TIMB_MATCH;
        if (trigger != PYBTIMER_MATCH_TRIGGER) {
            goto invalid_args;
        }
        break;
    default:
        break;
    }
    // special case for a 32-bit timer
    if (ch->channel == (TIMER_A | TIMER_B)) {
       ch->timer->irq_trigger |= (ch->timer->irq_trigger << 8);
    }

    void (*pfnHandler)(void);
    uint32_t intregister;
    switch (ch->timer->timer) {
    case TIMERA0_BASE:
        if (ch->channel == TIMER_B) {
            pfnHandler = &TIMER0BIntHandler;
            intregister = INT_TIMERA0B;
        } else {
            pfnHandler = &TIMER0AIntHandler;
            intregister = INT_TIMERA0A;
        }
        break;
    case TIMERA1_BASE:
        if (ch->channel == TIMER_B) {
            pfnHandler = &TIMER1BIntHandler;
            intregister = INT_TIMERA1B;
        } else {
            pfnHandler = &TIMER1AIntHandler;
            intregister = INT_TIMERA1A;
        }
        break;
    case TIMERA2_BASE:
        if (ch->channel == TIMER_B) {
            pfnHandler = &TIMER2BIntHandler;
            intregister = INT_TIMERA2B;
        } else {
            pfnHandler = &TIMER2AIntHandler;
            intregister = INT_TIMERA2A;
        }
        break;
    default:
        if (ch->channel == TIMER_B) {
            pfnHandler = &TIMER3BIntHandler;
            intregister = INT_TIMERA3B;
        } else {
            pfnHandler = &TIMER3AIntHandler;
            intregister = INT_TIMERA3A;
        }
        break;
    }

    // register the interrupt and configure the priority
    MAP_IntPrioritySet(intregister, priority);
    MAP_TimerIntRegister(ch->timer->timer, ch->channel, pfnHandler);

    // create the callback
    mp_obj_t _irq = mp_irq_new (ch, args[2].u_obj, &pyb_timer_channel_irq_methods);

    // enable the callback before returning
    pyb_timer_channel_irq_enable(ch);

    return _irq;

invalid_args:
    mp_raise_ValueError(mpexception_value_invalid_arguments);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_timer_channel_irq_obj, 1, pyb_timer_channel_irq);

STATIC const mp_rom_map_elem_t pyb_timer_channel_locals_dict_table[] = {
    // instance methods
    { MP_ROM_QSTR(MP_QSTR_freq),                 MP_ROM_PTR(&pyb_timer_channel_freq_obj) },
    { MP_ROM_QSTR(MP_QSTR_period),               MP_ROM_PTR(&pyb_timer_channel_period_obj) },
    { MP_ROM_QSTR(MP_QSTR_duty_cycle),           MP_ROM_PTR(&pyb_timer_channel_duty_cycle_obj) },
    { MP_ROM_QSTR(MP_QSTR_irq),                  MP_ROM_PTR(&pyb_timer_channel_irq_obj) },
};
STATIC MP_DEFINE_CONST_DICT(pyb_timer_channel_locals_dict, pyb_timer_channel_locals_dict_table);

STATIC const mp_obj_type_t pyb_timer_channel_type = {
    { &mp_type_type },
    .name = MP_QSTR_TimerChannel,
    .print = pyb_timer_channel_print,
    .locals_dict = (mp_obj_t)&pyb_timer_channel_locals_dict,
};