pwmout_api.c

00001 /* mbed Microcontroller Library
00002  * Copyright (c) 2006-2013 ARM Limited
00003  *
00004  * Licensed under the Apache License, Version 2.0 (the "License");
00005  * you may not use this file except in compliance with the License.
00006  * You may obtain a copy of the License at
00007  *
00008  *     http://www.apache.org/licenses/LICENSE-2.0
00009  *
00010  * Unless required by applicable law or agreed to in writing, software
00011  * distributed under the License is distributed on an "AS IS" BASIS,
00012  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00013  * See the License for the specific language governing permissions and
00014  * limitations under the License.
00015  */
00016 #include "pwmout_api.h"
00017 #include "cmsis.h"
00018 #include "pinmap.h"
00019 #include "error.h"
00020 
00021 #define TCR_CNT_EN       0x00000001
00022 #define TCR_RESET        0x00000002
00023 
00024 /* To have a PWM where we can change both the period and the duty cycle,
00025  * we need an entire timer. With the following conventions:
00026  *   * MR3 is used for the PWM period
00027  *   * MR0, MR1, MR2 are used for the duty cycle
00028  */
00029 static const PinMap PinMap_PWM[] = {
00030     /* CT16B0 */
00031     {P0_8 , PWM_1, 2}, {P1_13, PWM_1, 2},    /* MR0 */
00032     {P0_9 , PWM_2, 2}, {P1_14, PWM_2, 2},   /* MR1 */
00033     {P0_10, PWM_3, 3}, {P1_15, PWM_3, 2},   /* MR2 */
00034 
00035     /* CT16B1 */
00036     {P0_21, PWM_4, 1},                      /* MR0 */
00037     {P0_22, PWM_5, 2}, {P1_23, PWM_5, 1},   /* MR1 */
00038 
00039     /* CT32B0 */
00040     {P0_18, PWM_6, 2}, {P1_24, PWM_6, 1},   /* MR0 */
00041     {P0_19, PWM_7, 2}, {P1_25, PWM_7, 1},   /* MR1 */
00042     {P0_1 , PWM_8, 2}, {P1_26, PWM_8, 1},   /* MR2 */
00043 
00044     /* CT32B1 */
00045     {P0_13, PWM_9 , 3}, {P1_0, PWM_9 , 1},  /* MR0 */
00046     {P0_14, PWM_10, 3}, {P1_1, PWM_10, 1},  /* MR1 */
00047     {P0_15, PWM_11, 3}, {P1_2, PWM_11, 1},  /* MR2 */
00048 
00049     {NC, NC, 0}
00050 };
00051 
00052 typedef struct {
00053     uint8_t timer;
00054     uint8_t mr;
00055 } timer_mr;
00056 
00057 static timer_mr pwm_timer_map[11] = {
00058     {0, 0}, {0, 1}, {0, 2},
00059     {1, 0}, {1, 1},
00060     {2, 0}, {2, 1}, {2, 2},
00061     {3, 0}, {3, 1}, {3, 2},
00062 };
00063 
00064 static LPC_CTxxBx_Type *Timers[4] = {
00065     LPC_CT16B0, LPC_CT16B1,
00066     LPC_CT32B0, LPC_CT32B1
00067 };
00068 
00069 static unsigned int pwm_clock_mhz;
00070 
00071 void pwmout_init(pwmout_t* obj, PinName pin) {
00072     // determine the channel
00073     PWMName pwm = (PWMName)pinmap_peripheral(pin, PinMap_PWM);
00074     if (pwm == (uint32_t)NC)
00075         error("PwmOut pin mapping failed");
00076     
00077     obj->pwm = pwm;
00078     
00079     // Timer registers
00080     timer_mr tid = pwm_timer_map[pwm];
00081     LPC_CTxxBx_Type *timer = Timers[tid.timer];
00082     
00083     // Disable timer
00084     timer->TCR  = 0;
00085     
00086     // Power the correspondent timer
00087     LPC_SYSCON->SYSAHBCLKCTRL |= 1 << (tid.timer + 7);
00088     
00089     /* Enable PWM function */
00090     timer->PWMC  = (1 << 3)|(1 << 2)|(1 << 1)|(1 << 0);
00091     
00092     /* Reset Functionality on MR3 controlling the PWM period */
00093     timer->MCR  = 1 << 10;
00094     
00095     pwm_clock_mhz = SystemCoreClock / 1000000;
00096     
00097     // default to 20ms: standard for servos, and fine for e.g. brightness control
00098     pwmout_period_ms(obj, 20);
00099     pwmout_write    (obj, 0);
00100     
00101     // Wire pinout
00102     pinmap_pinout(pin, PinMap_PWM);
00103 }
00104 
00105 void pwmout_free(pwmout_t* obj) {
00106     // [TODO]
00107 }
00108 
00109 void pwmout_write(pwmout_t* obj, float value) {
00110     if (value < 0.0f) {
00111         value = 0.0;
00112     } else if (value > 1.0f) {
00113         value = 1.0;
00114     }
00115     
00116     timer_mr tid = pwm_timer_map[obj->pwm];
00117     LPC_CTxxBx_Type *timer = Timers[tid.timer];
00118     uint32_t t_off = timer->MR3  - (uint32_t)((float)(timer->MR3 ) * value);
00119     
00120     timer->TCR  = TCR_RESET;
00121     timer->MR [tid.mr] = t_off;
00122     timer->TCR  = TCR_CNT_EN;
00123 }
00124 
00125 float pwmout_read(pwmout_t* obj) {
00126     timer_mr tid = pwm_timer_map[obj->pwm];
00127     LPC_CTxxBx_Type *timer = Timers[tid.timer];
00128     
00129     float v = (float)(timer->MR3  - timer->MR [tid.mr]) / (float)(timer->MR3 );
00130     return (v > 1.0f) ? (1.0f) : (v);
00131 }
00132 
00133 void pwmout_period(pwmout_t* obj, float seconds) {
00134     pwmout_period_us(obj, seconds * 1000000.0f);
00135 }
00136 
00137 void pwmout_period_ms(pwmout_t* obj, int ms) {
00138     pwmout_period_us(obj, ms * 1000);
00139 }
00140 
00141 // Set the PWM period, keeping the duty cycle the same.
00142 void pwmout_period_us(pwmout_t* obj, int us) {
00143     int i = 0;
00144     uint32_t period_ticks = pwm_clock_mhz * us;
00145     
00146     timer_mr tid = pwm_timer_map[obj->pwm];
00147     LPC_CTxxBx_Type *timer = Timers[tid.timer];
00148     uint32_t old_period_ticks = timer->MR3 ;
00149     
00150     timer->TCR  = TCR_RESET;
00151     timer->MR3  = period_ticks;
00152     
00153     // Scale the pulse width to preserve the duty ratio
00154     if (old_period_ticks > 0) {
00155         for (i=0; i<3; i++) {
00156             uint32_t t_off = period_ticks - (uint32_t)(((uint64_t)timer->MR [i] * (uint64_t)period_ticks) / (uint64_t)old_period_ticks);
00157             timer->MR [i] = t_off;
00158         }
00159     }
00160     timer->TCR  = TCR_CNT_EN;
00161 }
00162 
00163 void pwmout_pulsewidth(pwmout_t* obj, float seconds) {
00164     pwmout_pulsewidth_us(obj, seconds * 1000000.0f);
00165 }
00166 
00167 void pwmout_pulsewidth_ms(pwmout_t* obj, int ms) {
00168     pwmout_pulsewidth_us(obj, ms * 1000);
00169 }
00170 
00171 void pwmout_pulsewidth_us(pwmout_t* obj, int us) {
00172     uint32_t t_on = (uint32_t)(((uint64_t)SystemCoreClock * (uint64_t)us) / (uint64_t)1000000);
00173     timer_mr tid = pwm_timer_map[obj->pwm];
00174     LPC_CTxxBx_Type *timer = Timers[tid.timer];
00175     
00176     timer->TCR  = TCR_RESET;
00177     if (t_on > timer->MR3 ) {
00178         pwmout_period_us(obj, us);
00179     }
00180     uint32_t t_off = timer->MR3  - t_on;
00181     timer->MR [tid.mr] = t_off;
00182     timer->TCR  = TCR_CNT_EN;
00183 }