us_ticker.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 <stddef.h>
00017 #include "us_ticker_api.h"
00018 #include "PeripheralNames.h"
00019 
00020 #define US_TICKER_TIMER_IRQn     SCT_IRQn
00021 
00022 int us_ticker_inited = 0;
00023 
00024 void us_ticker_init(void) {
00025     if (us_ticker_inited) return;
00026     us_ticker_inited = 1;
00027     
00028     // Enable the SCT clock
00029     LPC_SYSCON->SYSAHBCLKCTRL |= (1 << 8);
00030     
00031     // Clear peripheral reset the SCT:
00032     LPC_SYSCON->PRESETCTRL |= (1 << 8);
00033     
00034     // Unified counter (32 bits)
00035     LPC_SCT->CONFIG |= 1;
00036     
00037     // halt and clear the counter
00038     LPC_SCT->CTRL_L |= (1 << 2) | (1 << 3);
00039     
00040     // System Clock (12)MHz -> us_ticker (1)MHz
00041     LPC_SCT->CTRL_L |= ((SystemCoreClock/1000000 - 1) << 5);
00042     
00043     // unhalt the counter:
00044     //    - clearing bit 2 of the CTRL register
00045     LPC_SCT->CTRL_L &= ~(1 << 2);
00046     
00047     NVIC_SetVector(US_TICKER_TIMER_IRQn, (uint32_t)us_ticker_irq_handler);
00048     NVIC_EnableIRQ(US_TICKER_TIMER_IRQn);
00049 }
00050 
00051 uint32_t us_ticker_read() {
00052     if (!us_ticker_inited)
00053         us_ticker_init();
00054     
00055     return LPC_SCT->COUNT_U;
00056 }
00057 
00058 void us_ticker_set_interrupt(unsigned int timestamp) {
00059     // halt the counter: 
00060     //    - setting bit 2 of the CTRL register
00061     LPC_SCT->CTRL_L |= (1 << 2);
00062     
00063     // set timestamp in compare register
00064     LPC_SCT->MATCH[0].U = timestamp;
00065     
00066     // unhalt the counter:
00067     //    - clearing bit 2 of the CTRL register
00068     LPC_SCT->CTRL_L &= ~(1 << 2);
00069     
00070     // if events are not enabled, enable them
00071     if (!(LPC_SCT->EVEN & 0x01)) {
00072         
00073         // comb mode = match only
00074         LPC_SCT->EVENT[0].CTRL = (1 << 12);
00075         
00076         // ref manual:
00077         //   In simple applications that do not 
00078         //   use states, write 0x01 to this 
00079         //   register to enable an event
00080         LPC_SCT->EVENT[0].STATE |= 0x1;
00081         
00082         // enable events
00083         LPC_SCT->EVEN |= 0x1;
00084     }
00085 }
00086 
00087 void us_ticker_disable_interrupt(void) {
00088     LPC_SCT->EVEN &= ~1;
00089 }
00090 
00091 void us_ticker_clear_interrupt(void) {
00092     LPC_SCT->EVFLAG = 1;
00093 }