Diff: targets/TARGET_NXP/TARGET_LPC81X/us_ticker.c

Revision:

149:156823d33999

Parent:

144:ef7eb2e8f9f7

diff -r 21d94c44109e -r 156823d33999 targets/TARGET_NXP/TARGET_LPC81X/us_ticker.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/targets/TARGET_NXP/TARGET_LPC81X/us_ticker.c	Fri Oct 28 11:17:30 2016 +0100
@@ -0,0 +1,133 @@
+/* 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 <stddef.h>
+#include "us_ticker_api.h"
+#include "PeripheralNames.h"
+
+//New, using MRT instead of SCT, needed to free up SCT for PWM
+//Ported from LPC824 libs
+static int us_ticker_inited = 0;
+static int us_ticker_interrupt_inited = 0;
+unsigned int ticker_fullcount_us;
+unsigned long int ticker_expired_count_us = 0;
+int MRT_Clock_MHz;
+
+#define US_TICKER_TIMER_IRQn     MRT_IRQn
+
+void us_ticker_init(void) {
+    
+    if (us_ticker_inited)
+        return;
+
+    us_ticker_inited = 1;
+    
+    // Calculate MRT clock value (MRT has no prescaler)
+    MRT_Clock_MHz = (SystemCoreClock / 1000000);
+    // Calculate fullcounter value in us (MRT has 31 bits and clock is 30 MHz) 
+    ticker_fullcount_us = 0x80000000UL/MRT_Clock_MHz;
+
+    // Enable the MRT clock
+    LPC_SYSCON->SYSAHBCLKCTRL |= (1 << 10);
+
+    // Clear peripheral reset the MRT
+    LPC_SYSCON->PRESETCTRL |= (1 << 7);
+
+    // Force load interval value (Bit 0-30 is interval value, Bit 31 is Force Load bit)     
+    LPC_MRT->INTVAL0 = 0xFFFFFFFFUL;
+    // Enable Ch0 interrupt, Mode 0 is Repeat Interrupt
+    LPC_MRT->CTRL0 = (0x0 << 1) | (0x1 << 0);
+
+    // Force load interval value (Bit 0-30 is interval value, Bit 31 is Force Load bit)     
+    LPC_MRT->INTVAL1 = 0x80000000UL;
+    // Disable ch1 interrupt, Mode 0 is Repeat Interrupt
+    LPC_MRT->CTRL1 = (0x0 << 1) | (0x0 << 0);
+}
+
+void us_ticker_interrupt_init(void) {
+
+    if (us_ticker_interrupt_inited)
+        return;
+
+    us_ticker_interrupt_inited = 1;
+
+    // Set MRT interrupt vector
+    NVIC_SetVector(US_TICKER_TIMER_IRQn, (uint32_t)us_ticker_irq_handler);
+    NVIC_EnableIRQ(US_TICKER_TIMER_IRQn);
+}
+
+//TIMER0 is used for us ticker and timers (Timer, wait(), wait_us() etc)
+uint32_t us_ticker_read() {
+    
+    if (!us_ticker_inited)
+        us_ticker_init();
+
+    // Generate ticker value
+    // MRT source clock is SystemCoreClock (30MHz) and MRT is a 31-bit countdown timer
+    // Calculate expected value using current count and number of expired times to mimic a 32bit timer @ 1 MHz 
+    //
+    // ticker_expired_count_us
+    // The variable ticker_expired_count_us keeps track of the number of 31bits overflows (counted by TIMER0) and
+    // corrects that back to us counts.
+    //
+    // (0x7FFFFFFFUL - LPC_MRT->TIMER0)/MRT_Clock_MHz
+    // The counter is a 31bit downcounter from 7FFFFFFF so correct to actual count-up value and correct
+    // for 30 counts per us.
+    //
+    // Added up these 2 parts result in current us time returned as 32 bits.
+    return (0x7FFFFFFFUL - LPC_MRT->TIMER0)/MRT_Clock_MHz + ticker_expired_count_us;            
+}
+
+//TIMER1 is used for Timestamped interrupts (Ticker(), Timeout())
+void us_ticker_set_interrupt(timestamp_t timestamp) {
+    
+    if (!us_ticker_interrupt_inited)
+        us_ticker_interrupt_init();
+
+    // MRT source clock is SystemCoreClock (30MHz) and MRT is a 31-bit countdown timer    
+    // Force load interval value (Bit 0-30 is interval value, Bit 31 is Force Load bit)
+    // Note: The MRT has less counter headroom available than the typical mbed 32bit timer @ 1 MHz.
+    //       The calculated counter interval until the next timestamp will be truncated and an
+    //       'early' interrupt will be generated in case the max required count interval exceeds
+    //       the available 31 bits space. However, the mbed us_ticker interrupt handler will 
+    //       check current time against the next scheduled timestamp and simply re-issue the
+    //       same interrupt again when needed. The calculated counter interval will now be smaller.
+    LPC_MRT->INTVAL1 = (((timestamp - us_ticker_read()) * MRT_Clock_MHz) | 0x80000000UL);
+    
+    // Enable interrupt 
+    LPC_MRT->CTRL1 |= 1;
+}
+
+//Disable Timestamped interrupts triggered by TIMER1
+void us_ticker_disable_interrupt() {
+    //Timer1 for Timestamped interrupts (31 bits downcounter @ SystemCoreClock)    
+    LPC_MRT->CTRL1 &= ~1;
+}
+
+void us_ticker_clear_interrupt() {
+    
+    //Timer1 for Timestamped interrupts (31 bits downcounter @ SystemCoreClock)
+    if (LPC_MRT->STAT1 & 1)
+        LPC_MRT->STAT1 = 1;
+    
+    //Timer0 for us counter (31 bits downcounter @ SystemCoreClock)
+    if (LPC_MRT->STAT0 & 1) {
+        LPC_MRT->STAT0 = 1;
+        // ticker_expired_count_us = (ticker_expired * 0x80000000UL) / MRT_Clock_MHz
+        // The variable ticker_expired_count_us keeps track of the number of 31bits overflows (counted by TIMER0) and
+        // the multiplication/division corrects that back to us counts.
+        ticker_expired_count_us += ticker_fullcount_us;
+    }
+}