File content as of revision 596:d25a30803853:

/* mbed Microcontroller Library
 * Copyright (c) 2006-2013 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include "mbed_assert.h"
#include "pwmout_api.h"
#include "cmsis.h"
#include "pinmap.h"
#include "mbed_error.h"

#if DEVICE_PWMOUT

// bit flags for used SCTs
static unsigned char sct_used = 0;

static int get_available_sct()
{
    int i;
    for (i = 0; i < 4; i++) {
        if ((sct_used & (1 << i)) == 0)
            return i;
    }
    return -1;
}

void pwmout_init(pwmout_t* obj, PinName pin)
{
    MBED_ASSERT(pin != (PinName)NC);

    int sct_n = get_available_sct();
    if (sct_n == -1) {
        error("No available SCT");
    }

    sct_used |= (1 << sct_n);

    obj->pwm =  (LPC_SCT_Type*)LPC_SCT;
    obj->pwm_ch = sct_n;

    LPC_SCT_Type* pwm = obj->pwm;

    // Enable the SCT clock
    LPC_SYSCON->SYSAHBCLKCTRL |= (1 << 8);

    // Clear peripheral reset the SCT:
    LPC_SYSCON->PRESETCTRL |=  (1 << 8);

    switch(sct_n) {
        case 0:
            // SCT_OUT0
            LPC_SWM->PINASSIGN[7] &= ~0xFF000000;
            LPC_SWM->PINASSIGN[7] |= ((pin >> PIN_SHIFT) << 24);
            break;
        case 1:
            // SCT_OUT1
            LPC_SWM->PINASSIGN[8] &= ~0x000000FF;
            LPC_SWM->PINASSIGN[8] |= (pin >> PIN_SHIFT);
            break;
        case 2:
            // SCT2_OUT2
            LPC_SWM->PINASSIGN[8] &= ~0x0000FF00;
            LPC_SWM->PINASSIGN[8] |= ((pin >> PIN_SHIFT) << 8);
            break;
        case 3:
            // SCT3_OUT3
            LPC_SWM->PINASSIGN[8] &= ~0x00FF0000;
            LPC_SWM->PINASSIGN[8] |= ((pin >> PIN_SHIFT) << 16);
            break;
        default:
            break;
    }

    // Unified 32-bit counter, autolimit
    pwm->CONFIG |= ((0x3 << 17) | 0x01);

    // halt and clear the counter
    pwm->CTRL |= (1 << 2) | (1 << 3);

    // System Clock -> us_ticker (1)MHz
    pwm->CTRL &= ~(0x7F << 5);
    pwm->CTRL |= (((SystemCoreClock/1000000 - 1) & 0x7F) << 5);

    pwm->OUT[sct_n].SET = (1 << ((sct_n * 2) + 0));
    pwm->OUT[sct_n].CLR = (1 << ((sct_n * 2) + 1));

    pwm->EVENT[(sct_n * 2) + 0].CTRL  = (1 << 12) | ((sct_n * 2) + 0);  // match event
    pwm->EVENT[(sct_n * 2) + 0].STATE = 0xFFFFFFFF;
    pwm->EVENT[(sct_n * 2) + 1].CTRL  = (1 << 12) | ((sct_n * 2) + 1);
    pwm->EVENT[(sct_n * 2) + 1].STATE = 0xFFFFFFFF;

    // unhalt the counter:
    //    - clearing bit 2 of the CTRL register
    pwm->CTRL &= ~(1 << 2);

    // default to 20ms: standard for servos, and fine for e.g. brightness control
    pwmout_period_ms(obj, 20);
    pwmout_write    (obj, 0);
}

void pwmout_free(pwmout_t* obj)
{
    // Disable the SCT clock
    LPC_SYSCON->SYSAHBCLKCTRL &= ~(1 << 8);
    sct_used &= ~(1 << obj->pwm_ch);
}

void pwmout_write(pwmout_t* obj, float value)
{
    if (value < 0.0f) {
        value = 0.0;
    } else if (value > 1.0f) {
        value = 1.0;
    }
    uint32_t t_on = (uint32_t)((float)(obj->pwm->MATCHREL[obj->pwm_ch * 2]) * value);
    obj->pwm->MATCHREL[(obj->pwm_ch * 2) + 1] = t_on;
}

float pwmout_read(pwmout_t* obj)
{
    uint32_t t_off = obj->pwm->MATCHREL[(obj->pwm_ch * 2) + 0];
    uint32_t t_on  = obj->pwm->MATCHREL[(obj->pwm_ch * 2) + 1];
    float v = (float)t_on/(float)t_off;
    return (v > 1.0f) ? (1.0f) : (v);
}

void pwmout_period(pwmout_t* obj, float seconds)
{
    pwmout_period_us(obj, seconds * 1000000.0f);
}

void pwmout_period_ms(pwmout_t* obj, int ms)
{
    pwmout_period_us(obj, ms * 1000);
}

// Set the PWM period, keeping the duty cycle the same.
void pwmout_period_us(pwmout_t* obj, int us)
{
    uint32_t t_off = obj->pwm->MATCHREL[(obj->pwm_ch * 2) + 0];
    uint32_t t_on  = obj->pwm->MATCHREL[(obj->pwm_ch * 2) + 1];
    float v = (float)t_on/(float)t_off;
    obj->pwm->MATCHREL[(obj->pwm_ch * 2) + 0] = (uint32_t)us;
    obj->pwm->MATCHREL[(obj->pwm_ch * 2) + 1] = (uint32_t)((float)us * (float)v);
}

void pwmout_pulsewidth(pwmout_t* obj, float seconds)
{
    pwmout_pulsewidth_us(obj, seconds * 1000000.0f);
}

void pwmout_pulsewidth_ms(pwmout_t* obj, int ms)
{
    pwmout_pulsewidth_us(obj, ms * 1000);
}

void pwmout_pulsewidth_us(pwmout_t* obj, int us)
{
    obj->pwm->MATCHREL[(obj->pwm_ch * 2) + 1] = (uint32_t)us;
}

#endif