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Last commit 20 Feb 2019 by mbed official

targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c@495:01cb89f68337, 2015-03-20 (annotated)

Committer:
mbed_official
Date:
Fri Mar 20 09:30:08 2015 +0000
Revision:
495:01cb89f68337
Parent:
453:a290c6acf95e
Child:
603:3c75ef011213
Synchronized with git revision d1d900d30c656b1f35f4f5db49e47ea199b0b8d6



Full URL: https://github.com/mbedmicro/mbed/commit/d1d900d30c656b1f35f4f5db49e47ea199b0b8d6/

Who changed what in which revision?

UserRevisionLine numberNew contents of line
mbed_official 85:e1a8e879a6a9 1 /* mbed Microcontroller Library
mbed_official 104:a6a92e2e5a92 2 * Copyright (c) 2013 Nordic Semiconductor
mbed_official 85:e1a8e879a6a9 3 *
mbed_official 85:e1a8e879a6a9 4 * Licensed under the Apache License, Version 2.0 (the "License");
mbed_official 85:e1a8e879a6a9 5 * you may not use this file except in compliance with the License.
mbed_official 85:e1a8e879a6a9 6 * You may obtain a copy of the License at
mbed_official 85:e1a8e879a6a9 7 *
mbed_official 85:e1a8e879a6a9 8 * http://www.apache.org/licenses/LICENSE-2.0
mbed_official 85:e1a8e879a6a9 9 *
mbed_official 85:e1a8e879a6a9 10 * Unless required by applicable law or agreed to in writing, software
mbed_official 85:e1a8e879a6a9 11 * distributed under the License is distributed on an "AS IS" BASIS,
mbed_official 85:e1a8e879a6a9 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
mbed_official 85:e1a8e879a6a9 13 * See the License for the specific language governing permissions and
mbed_official 85:e1a8e879a6a9 14 * limitations under the License.
mbed_official 85:e1a8e879a6a9 15 */
mbed_official 85:e1a8e879a6a9 16 #include <stddef.h>
mbed_official 495:01cb89f68337 17 #include <stdbool.h>
mbed_official 85:e1a8e879a6a9 18 #include "us_ticker_api.h"
mbed_official 85:e1a8e879a6a9 19 #include "cmsis.h"
mbed_official 85:e1a8e879a6a9 20 #include "PeripheralNames.h"
mbed_official 495:01cb89f68337 21 #include "nrf_delay.h"
mbed_official 495:01cb89f68337 22
mbed_official 495:01cb89f68337 23 /*
mbed_official 495:01cb89f68337 24 * Note: The micro-second timer API on the nRF51 platform is implemented using
mbed_official 495:01cb89f68337 25 * the RTC counter run at 32kHz (sourced from an external oscillator). This is
mbed_official 495:01cb89f68337 26 * a trade-off between precision and power. Running a normal 32-bit MCU counter
mbed_official 495:01cb89f68337 27 * at high frequency causes the average power consumption to rise to a few
mbed_official 495:01cb89f68337 28 * hundred micro-amps, which is prohibitive for typical low-power BLE
mbed_official 495:01cb89f68337 29 * applications.
mbed_official 495:01cb89f68337 30 * A 32kHz clock doesn't offer the precision needed for keeping u-second time,
mbed_official 495:01cb89f68337 31 * but we're assuming that this will not be a problem for the average user.
mbed_official 495:01cb89f68337 32 */
mbed_official 495:01cb89f68337 33
mbed_official 495:01cb89f68337 34 #define MAX_RTC_COUNTER_VAL 0x00FFFFFF /**< Maximum value of the RTC counter. */
mbed_official 495:01cb89f68337 35 #define RTC_CLOCK_FREQ (uint32_t)(32768)
mbed_official 495:01cb89f68337 36 #define RTC1_IRQ_PRI 3 /**< Priority of the RTC1 interrupt (used
mbed_official 495:01cb89f68337 37 * for checking for timeouts and executing
mbed_official 495:01cb89f68337 38 * timeout handlers). This must be the same
mbed_official 495:01cb89f68337 39 * as APP_IRQ_PRIORITY_LOW; taken from the
mbed_official 495:01cb89f68337 40 * Nordic SDK. */
mbed_official 495:01cb89f68337 41 #define MAX_RTC_TASKS_DELAY 47 /**< Maximum delay until an RTC task is executed. */
mbed_official 495:01cb89f68337 42
mbed_official 495:01cb89f68337 43 #define FUZZY_RTC_TICKS 2 /* RTC COMPARE occurs when a CC register is N and the RTC
mbed_official 495:01cb89f68337 44 * COUNTER value transitions from N-1 to N. If we're trying to
mbed_official 495:01cb89f68337 45 * setup a callback for a time which will arrive very shortly,
mbed_official 495:01cb89f68337 46 * there are limits to how short the callback interval may be for us
mbed_official 495:01cb89f68337 47 * to rely upon the RTC Compare trigger. If the COUNTER is N,
mbed_official 495:01cb89f68337 48 * writing N+2 to a CC register is guaranteed to trigger a COMPARE
mbed_official 495:01cb89f68337 49 * event at N+2. */
mbed_official 495:01cb89f68337 50
mbed_official 495:01cb89f68337 51 #define RTC_UNITS_TO_MICROSECONDS(RTC_UNITS) (((RTC_UNITS) * (uint64_t)1000000) / RTC_CLOCK_FREQ)
mbed_official 495:01cb89f68337 52 #define MICROSECONDS_TO_RTC_UNITS(MICROS) ((((uint64_t)(MICROS) * RTC_CLOCK_FREQ) + 999999) / 1000000)
mbed_official 495:01cb89f68337 53
mbed_official 495:01cb89f68337 54 static bool us_ticker_inited = false;
mbed_official 495:01cb89f68337 55 static volatile uint32_t overflowCount; /**< The number of times the 24-bit RTC counter has overflowed. */
mbed_official 495:01cb89f68337 56 static volatile bool us_ticker_callbackPending = false;
mbed_official 495:01cb89f68337 57 static uint32_t us_ticker_callbackTimestamp;
mbed_official 495:01cb89f68337 58
mbed_official 495:01cb89f68337 59 static inline void rtc1_enableCompareInterrupt(void)
mbed_official 495:01cb89f68337 60 {
mbed_official 495:01cb89f68337 61 NRF_RTC1->EVTENCLR = RTC_EVTEN_COMPARE0_Msk;
mbed_official 495:01cb89f68337 62 NRF_RTC1->INTENSET = RTC_INTENSET_COMPARE0_Msk;
mbed_official 495:01cb89f68337 63 }
mbed_official 495:01cb89f68337 64
mbed_official 495:01cb89f68337 65 static inline void rtc1_disableCompareInterrupt(void)
mbed_official 495:01cb89f68337 66 {
mbed_official 495:01cb89f68337 67 NRF_RTC1->INTENCLR = RTC_INTENSET_COMPARE0_Msk;
mbed_official 495:01cb89f68337 68 NRF_RTC1->EVTENCLR = RTC_EVTEN_COMPARE0_Msk;
mbed_official 495:01cb89f68337 69 }
mbed_official 495:01cb89f68337 70
mbed_official 495:01cb89f68337 71 static inline void rtc1_enableOverflowInterrupt(void)
mbed_official 495:01cb89f68337 72 {
mbed_official 495:01cb89f68337 73 NRF_RTC1->EVTENCLR = RTC_EVTEN_OVRFLW_Msk;
mbed_official 495:01cb89f68337 74 NRF_RTC1->INTENSET = RTC_INTENSET_OVRFLW_Msk;
mbed_official 495:01cb89f68337 75 }
mbed_official 495:01cb89f68337 76
mbed_official 495:01cb89f68337 77 static inline void rtc1_disableOverflowInterrupt(void)
mbed_official 495:01cb89f68337 78 {
mbed_official 495:01cb89f68337 79 NRF_RTC1->INTENCLR = RTC_INTENSET_OVRFLW_Msk;
mbed_official 495:01cb89f68337 80 NRF_RTC1->EVTENCLR = RTC_EVTEN_OVRFLW_Msk;
mbed_official 495:01cb89f68337 81 }
mbed_official 495:01cb89f68337 82
mbed_official 495:01cb89f68337 83 static inline void invokeCallback(void)
mbed_official 495:01cb89f68337 84 {
mbed_official 495:01cb89f68337 85 us_ticker_callbackPending = false;
mbed_official 495:01cb89f68337 86 rtc1_disableCompareInterrupt();
mbed_official 495:01cb89f68337 87 us_ticker_irq_handler();
mbed_official 495:01cb89f68337 88 }
mbed_official 127:ce7cebc0511f 89
mbed_official 495:01cb89f68337 90 /**
mbed_official 495:01cb89f68337 91 * @brief Function for starting the RTC1 timer. The RTC timer is expected to
mbed_official 495:01cb89f68337 92 * keep running--some interrupts may be disabled temporarily.
mbed_official 495:01cb89f68337 93 */
mbed_official 495:01cb89f68337 94 static void rtc1_start()
mbed_official 495:01cb89f68337 95 {
mbed_official 495:01cb89f68337 96 NRF_RTC1->PRESCALER = 0; /* for no pre-scaling. */
mbed_official 495:01cb89f68337 97
mbed_official 495:01cb89f68337 98 rtc1_enableOverflowInterrupt();
mbed_official 495:01cb89f68337 99
mbed_official 495:01cb89f68337 100 NVIC_SetPriority(RTC1_IRQn, RTC1_IRQ_PRI);
mbed_official 495:01cb89f68337 101 NVIC_ClearPendingIRQ(RTC1_IRQn);
mbed_official 495:01cb89f68337 102 NVIC_EnableIRQ(RTC1_IRQn);
mbed_official 495:01cb89f68337 103
mbed_official 495:01cb89f68337 104 NRF_RTC1->TASKS_START = 1;
mbed_official 495:01cb89f68337 105 nrf_delay_us(MAX_RTC_TASKS_DELAY);
mbed_official 495:01cb89f68337 106 }
mbed_official 495:01cb89f68337 107
mbed_official 495:01cb89f68337 108 /**
mbed_official 495:01cb89f68337 109 * @brief Function for stopping the RTC1 timer. We don't expect to call this.
mbed_official 495:01cb89f68337 110 */
mbed_official 495:01cb89f68337 111 void rtc1_stop(void)
mbed_official 495:01cb89f68337 112 {
mbed_official 495:01cb89f68337 113 NVIC_DisableIRQ(RTC1_IRQn);
mbed_official 495:01cb89f68337 114 rtc1_disableCompareInterrupt();
mbed_official 495:01cb89f68337 115 rtc1_disableOverflowInterrupt();
mbed_official 495:01cb89f68337 116
mbed_official 495:01cb89f68337 117 NRF_RTC1->TASKS_STOP = 1;
mbed_official 495:01cb89f68337 118 nrf_delay_us(MAX_RTC_TASKS_DELAY);
mbed_official 495:01cb89f68337 119
mbed_official 495:01cb89f68337 120 NRF_RTC1->TASKS_CLEAR = 1;
mbed_official 495:01cb89f68337 121 nrf_delay_us(MAX_RTC_TASKS_DELAY);
mbed_official 495:01cb89f68337 122 }
mbed_official 495:01cb89f68337 123
mbed_official 495:01cb89f68337 124 /**
mbed_official 495:01cb89f68337 125 * @brief Function for returning the current value of the RTC1 counter.
mbed_official 495:01cb89f68337 126 *
mbed_official 495:01cb89f68337 127 * @return Current RTC1 counter as a 64-bit value with 56-bit precision (even
mbed_official 495:01cb89f68337 128 * though the underlying counter is 24-bit)
mbed_official 495:01cb89f68337 129 */
mbed_official 495:01cb89f68337 130 static inline uint64_t rtc1_getCounter64(void)
mbed_official 495:01cb89f68337 131 {
mbed_official 495:01cb89f68337 132 if (NRF_RTC1->EVENTS_OVRFLW) {
mbed_official 495:01cb89f68337 133 overflowCount++;
mbed_official 495:01cb89f68337 134 NRF_RTC1->EVENTS_OVRFLW = 0;
mbed_official 495:01cb89f68337 135 NRF_RTC1->EVTENCLR = RTC_EVTEN_OVRFLW_Msk;
mbed_official 495:01cb89f68337 136 }
mbed_official 495:01cb89f68337 137 return ((uint64_t)overflowCount << 24) | NRF_RTC1->COUNTER;
mbed_official 495:01cb89f68337 138 }
mbed_official 495:01cb89f68337 139
mbed_official 495:01cb89f68337 140 /**
mbed_official 495:01cb89f68337 141 * @brief Function for returning the current value of the RTC1 counter.
mbed_official 495:01cb89f68337 142 *
mbed_official 495:01cb89f68337 143 * @return Current RTC1 counter as a 32-bit value (even though the underlying counter is 24-bit)
mbed_official 495:01cb89f68337 144 */
mbed_official 495:01cb89f68337 145 static inline uint32_t rtc1_getCounter(void)
mbed_official 495:01cb89f68337 146 {
mbed_official 495:01cb89f68337 147 return rtc1_getCounter64();
mbed_official 495:01cb89f68337 148 }
mbed_official 495:01cb89f68337 149
mbed_official 495:01cb89f68337 150 /**
mbed_official 495:01cb89f68337 151 * @brief Function for handling the RTC1 interrupt.
mbed_official 495:01cb89f68337 152 *
mbed_official 495:01cb89f68337 153 * @details Checks for timeouts, and executes timeout handlers for expired timers.
mbed_official 495:01cb89f68337 154 */
mbed_official 495:01cb89f68337 155 void RTC1_IRQHandler(void)
mbed_official 495:01cb89f68337 156 {
mbed_official 495:01cb89f68337 157 if (NRF_RTC1->EVENTS_OVRFLW) {
mbed_official 495:01cb89f68337 158 overflowCount++;
mbed_official 495:01cb89f68337 159 NRF_RTC1->EVENTS_OVRFLW = 0;
mbed_official 495:01cb89f68337 160 NRF_RTC1->EVTENCLR = RTC_EVTEN_OVRFLW_Msk;
mbed_official 495:01cb89f68337 161 }
mbed_official 495:01cb89f68337 162 if (NRF_RTC1->EVENTS_COMPARE[0] && us_ticker_callbackPending && ((int)(us_ticker_callbackTimestamp - rtc1_getCounter()) <= 0)) {
mbed_official 495:01cb89f68337 163 NRF_RTC1->EVENTS_COMPARE[0] = 0;
mbed_official 495:01cb89f68337 164 NRF_RTC1->EVTENCLR = RTC_EVTEN_COMPARE0_Msk;
mbed_official 495:01cb89f68337 165 invokeCallback();
mbed_official 495:01cb89f68337 166 }
mbed_official 495:01cb89f68337 167 }
mbed_official 300:55638feb26a4 168
mbed_official 300:55638feb26a4 169 void us_ticker_init(void)
mbed_official 300:55638feb26a4 170 {
mbed_official 304:89b9c3a9a045 171 if (us_ticker_inited) {
mbed_official 85:e1a8e879a6a9 172 return;
mbed_official 85:e1a8e879a6a9 173 }
mbed_official 300:55638feb26a4 174
mbed_official 495:01cb89f68337 175 rtc1_start();
mbed_official 304:89b9c3a9a045 176 us_ticker_inited = true;
mbed_official 85:e1a8e879a6a9 177 }
mbed_official 85:e1a8e879a6a9 178
mbed_official 300:55638feb26a4 179 uint32_t us_ticker_read()
mbed_official 300:55638feb26a4 180 {
mbed_official 304:89b9c3a9a045 181 if (!us_ticker_inited) {
mbed_official 304:89b9c3a9a045 182 us_ticker_init();
mbed_official 304:89b9c3a9a045 183 }
mbed_official 304:89b9c3a9a045 184
mbed_official 495:01cb89f68337 185 /* Return a pseudo microsecond counter value. This is only as precise as the
mbed_official 495:01cb89f68337 186 * 32khz low-freq clock source, but could be adequate.*/
mbed_official 495:01cb89f68337 187 return RTC_UNITS_TO_MICROSECONDS(rtc1_getCounter64());
mbed_official 304:89b9c3a9a045 188 }
mbed_official 304:89b9c3a9a045 189
mbed_official 495:01cb89f68337 190 /**
mbed_official 495:01cb89f68337 191 * Setup the us_ticker callback interrupt to go at the given timestamp.
mbed_official 495:01cb89f68337 192 *
mbed_official 495:01cb89f68337 193 * @Note: Only one callback is pending at any time.
mbed_official 495:01cb89f68337 194 *
mbed_official 495:01cb89f68337 195 * @Note: If a callback is pending, and this function is called again, the new
mbed_official 495:01cb89f68337 196 * callback-time overrides the existing callback setting. It is the caller's
mbed_official 495:01cb89f68337 197 * responsibility to ensure that this function is called to setup a callback for
mbed_official 495:01cb89f68337 198 * the earliest timeout.
mbed_official 495:01cb89f68337 199 *
mbed_official 495:01cb89f68337 200 * @Note: If this function is used to setup an interrupt which is immediately
mbed_official 495:01cb89f68337 201 * pending--such as for 'now' or a time in the past,--then the callback is
mbed_official 495:01cb89f68337 202 * invoked a few ticks later.
mbed_official 495:01cb89f68337 203 */
mbed_official 304:89b9c3a9a045 204 void us_ticker_set_interrupt(timestamp_t timestamp)
mbed_official 304:89b9c3a9a045 205 {
mbed_official 304:89b9c3a9a045 206 if (!us_ticker_inited) {
mbed_official 85:e1a8e879a6a9 207 us_ticker_init();
mbed_official 85:e1a8e879a6a9 208 }
mbed_official 300:55638feb26a4 209
mbed_official 495:01cb89f68337 210 /*
mbed_official 495:01cb89f68337 211 * The argument to this function is a 32-bit microsecond timestamp for when
mbed_official 495:01cb89f68337 212 * a callback should be invoked. On the nRF51, we use an RTC timer running
mbed_official 495:01cb89f68337 213 * at 32kHz to implement a low-power us-ticker. This results in a problem
mbed_official 495:01cb89f68337 214 * based on the fact that 1000000 is not a multiple of 32768.
mbed_official 495:01cb89f68337 215 *
mbed_official 495:01cb89f68337 216 * Going from a micro-second based timestamp to a 32kHz based RTC-time is a
mbed_official 495:01cb89f68337 217 * linear mapping; but this mapping doesn't preserve wraparounds--i.e. when
mbed_official 495:01cb89f68337 218 * the 32-bit micro-second timestamp wraps around unfortunately the
mbed_official 495:01cb89f68337 219 * underlying RTC counter doesn't. The result is that timestamp expiry
mbed_official 495:01cb89f68337 220 * checks on micro-second timestamps don't yield the same result when
mbed_official 495:01cb89f68337 221 * applied on the corresponding RTC timestamp values.
mbed_official 495:01cb89f68337 222 *
mbed_official 495:01cb89f68337 223 * One solution is to translate the incoming 32-bit timestamp into a virtual
mbed_official 495:01cb89f68337 224 * 64-bit timestamp based on the knowledge of system-uptime, and then use
mbed_official 495:01cb89f68337 225 * this wraparound-free 64-bit value to do a linear mapping to RTC time.
mbed_official 495:01cb89f68337 226 * System uptime on an nRF is maintained using the 24-bit RTC counter. We
mbed_official 495:01cb89f68337 227 * track the overflow count to extend the 24-bit hardware counter by an
mbed_official 495:01cb89f68337 228 * additional 32 bits. RTC_UNITS_TO_MICROSECONDS() converts this into
mbed_official 495:01cb89f68337 229 * microsecond units (in 64-bits).
mbed_official 495:01cb89f68337 230 */
mbed_official 495:01cb89f68337 231 const uint64_t currentTime64 = RTC_UNITS_TO_MICROSECONDS(rtc1_getCounter64());
mbed_official 495:01cb89f68337 232 uint64_t timestamp64 = (currentTime64 & ~(uint64_t)0xFFFFFFFFULL) + timestamp;
mbed_official 495:01cb89f68337 233 if (((uint32_t)currentTime64 > 0x80000000) && (timestamp < 0x80000000)) {
mbed_official 495:01cb89f68337 234 timestamp64 += (uint64_t)0x100000000ULL;
mbed_official 300:55638feb26a4 235 }
mbed_official 495:01cb89f68337 236 uint32_t newCallbackTime = MICROSECONDS_TO_RTC_UNITS(timestamp64);
mbed_official 85:e1a8e879a6a9 237
mbed_official 495:01cb89f68337 238 /* Check for repeat setup of an existing callback. This is actually not
mbed_official 495:01cb89f68337 239 * important; the following code should work even without this check. */
mbed_official 495:01cb89f68337 240 if (us_ticker_callbackPending && (newCallbackTime == us_ticker_callbackTimestamp)) {
mbed_official 304:89b9c3a9a045 241 return;
mbed_official 300:55638feb26a4 242 }
mbed_official 300:55638feb26a4 243
mbed_official 495:01cb89f68337 244 /* Check for callbacks which are immediately (or will *very* shortly become) pending.
mbed_official 495:01cb89f68337 245 * Even if they are immediately pending, they are scheduled to trigger a few
mbed_official 495:01cb89f68337 246 * ticks later. This keeps things simple by invoking the callback from an
mbed_official 495:01cb89f68337 247 * independent interrupt context. */
mbed_official 495:01cb89f68337 248 if ((int)(newCallbackTime - rtc1_getCounter()) <= (int)FUZZY_RTC_TICKS) {
mbed_official 495:01cb89f68337 249 newCallbackTime = rtc1_getCounter() + FUZZY_RTC_TICKS;
mbed_official 300:55638feb26a4 250 }
mbed_official 361:56c2a6244bba 251
mbed_official 495:01cb89f68337 252 NRF_RTC1->CC[0] = newCallbackTime & MAX_RTC_COUNTER_VAL;
mbed_official 495:01cb89f68337 253 us_ticker_callbackTimestamp = newCallbackTime;
mbed_official 495:01cb89f68337 254 if (!us_ticker_callbackPending) {
mbed_official 495:01cb89f68337 255 us_ticker_callbackPending = true;
mbed_official 495:01cb89f68337 256 rtc1_enableCompareInterrupt();
mbed_official 361:56c2a6244bba 257 }
mbed_official 85:e1a8e879a6a9 258 }
mbed_official 85:e1a8e879a6a9 259
mbed_official 300:55638feb26a4 260 void us_ticker_disable_interrupt(void)
mbed_official 300:55638feb26a4 261 {
mbed_official 495:01cb89f68337 262 if (us_ticker_callbackPending) {
mbed_official 495:01cb89f68337 263 rtc1_disableCompareInterrupt();
mbed_official 495:01cb89f68337 264 us_ticker_callbackPending = false;
mbed_official 304:89b9c3a9a045 265 }
mbed_official 85:e1a8e879a6a9 266 }
mbed_official 300:55638feb26a4 267
mbed_official 300:55638feb26a4 268 void us_ticker_clear_interrupt(void)
mbed_official 300:55638feb26a4 269 {
mbed_official 495:01cb89f68337 270 NRF_RTC1->EVENTS_OVRFLW = 0;
mbed_official 495:01cb89f68337 271 NRF_RTC1->EVENTS_COMPARE[0] = 0;
mbed_official 85:e1a8e879a6a9 272 }