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 //  PORT ID, PWM ID, Pin function
00025 static const PinMap PinMap_PWM[] = {
00026     {P1_18, PWM_1, 2},
00027     {P1_20, PWM_2, 2},
00028     {P1_21, PWM_3, 2},
00029     {P1_23, PWM_4, 2},
00030     {P1_24, PWM_5, 2},
00031     {P1_26, PWM_6, 2},
00032     {P2_0 , PWM_1, 1},
00033     {P2_1 , PWM_2, 1},
00034     {P2_2 , PWM_3, 1},
00035     {P2_3 , PWM_4, 1},
00036     {P2_4 , PWM_5, 1},
00037     {P2_5 , PWM_6, 1},
00038     {P3_25, PWM_2, 3},
00039     {P3_26, PWM_3, 3},
00040     {NC, NC, 0}
00041 };
00042 
00043 __IO uint32_t *PWM_MATCH[] = {
00044     &(LPC_PWM1->MR0),
00045     &(LPC_PWM1->MR1),
00046     &(LPC_PWM1->MR2),
00047     &(LPC_PWM1->MR3),
00048     &(LPC_PWM1->MR4),
00049     &(LPC_PWM1->MR5),
00050     &(LPC_PWM1->MR6)
00051 };
00052 
00053 #define TCR_PWM_EN       0x00000008
00054 
00055 static unsigned int pwm_clock_mhz;
00056 
00057 void pwmout_init(pwmout_t* obj, PinName pin) {
00058     // determine the channel
00059     PWMName pwm = (PWMName)pinmap_peripheral(pin, PinMap_PWM);
00060     if (pwm == (uint32_t)NC)
00061         error("PwmOut pin mapping failed");
00062     
00063     obj->pwm = pwm;
00064     obj->MR = PWM_MATCH[pwm];
00065     
00066     // ensure the power is on
00067     LPC_SC->PCONP |= 1 << 6;
00068     
00069     // ensure clock to /4
00070     LPC_SC->PCLKSEL0 &= ~(0x3 << 12);     // pclk = /4
00071     LPC_PWM1->PR = 0;                     // no pre-scale
00072     
00073     // ensure single PWM mode
00074     LPC_PWM1->MCR = 1 << 1; // reset TC on match 0
00075     
00076     // enable the specific PWM output
00077     LPC_PWM1->PCR |= 1 << (8 + pwm);
00078     
00079     pwm_clock_mhz = SystemCoreClock / 4000000;
00080     
00081     // default to 20ms: standard for servos, and fine for e.g. brightness control
00082     pwmout_period_ms(obj, 20);
00083     pwmout_write    (obj, 0);
00084     
00085     // Wire pinout
00086     pinmap_pinout(pin, PinMap_PWM);
00087 }
00088 
00089 void pwmout_free(pwmout_t* obj) {
00090     // [TODO]
00091 }
00092 
00093 void pwmout_write(pwmout_t* obj, float value) {
00094     if (value < 0.0f) {
00095         value = 0.0;
00096     } else if (value > 1.0f) {
00097         value = 1.0;
00098     }
00099     
00100     // set channel match to percentage
00101     uint32_t v = (uint32_t)((float)(LPC_PWM1->MR0) * value);
00102     
00103     // workaround for PWM1[1] - Never make it equal MR0, else we get 1 cycle dropout
00104     if (v == LPC_PWM1->MR0) {
00105         v++;
00106     }
00107     
00108     *obj->MR = v;
00109     
00110     // accept on next period start
00111     LPC_PWM1->LER |= 1 << obj->pwm;
00112 }
00113 
00114 float pwmout_read(pwmout_t* obj) {
00115     float v = (float)(*obj->MR) / (float)(LPC_PWM1->MR0);
00116     return (v > 1.0f) ? (1.0f) : (v);
00117 }
00118 
00119 void pwmout_period(pwmout_t* obj, float seconds) {
00120     pwmout_period_us(obj, seconds * 1000000.0f);
00121 }
00122 
00123 void pwmout_period_ms(pwmout_t* obj, int ms) {
00124     pwmout_period_us(obj, ms * 1000);
00125 }
00126 
00127 // Set the PWM period, keeping the duty cycle the same.
00128 void pwmout_period_us(pwmout_t* obj, int us) {
00129     // calculate number of ticks
00130     uint32_t ticks = pwm_clock_mhz * us;
00131     
00132     // set reset
00133     LPC_PWM1->TCR = TCR_RESET;
00134     
00135     // set the global match register
00136     LPC_PWM1->MR0 = ticks;
00137     
00138     // Scale the pulse width to preserve the duty ratio
00139     if (LPC_PWM1->MR0 > 0) {
00140         *obj->MR = (*obj->MR * ticks) / LPC_PWM1->MR0;
00141     }
00142     
00143     // set the channel latch to update value at next period start
00144     LPC_PWM1->LER |= 1 << 0;
00145     
00146     // enable counter and pwm, clear reset
00147     LPC_PWM1->TCR = TCR_CNT_EN | TCR_PWM_EN;
00148 }
00149 
00150 void pwmout_pulsewidth(pwmout_t* obj, float seconds) {
00151     pwmout_pulsewidth_us(obj, seconds * 1000000.0f);
00152 }
00153 
00154 void pwmout_pulsewidth_ms(pwmout_t* obj, int ms) {
00155     pwmout_pulsewidth_us(obj, ms * 1000);
00156 }
00157 
00158 void pwmout_pulsewidth_us(pwmout_t* obj, int us) {
00159     // calculate number of ticks
00160     uint32_t v = pwm_clock_mhz * us;
00161     
00162     // workaround for PWM1[1] - Never make it equal MR0, else we get 1 cycle dropout
00163     if (v == LPC_PWM1->MR0) {
00164         v++;
00165     }
00166     
00167     // set the match register value
00168     *obj->MR = v;
00169     
00170     // set the channel latch to update value at next period start
00171     LPC_PWM1->LER |= 1 << obj->pwm;
00172 }