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Diff: targets/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c
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diff -r 21d94c44109e -r 156823d33999 targets/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/targets/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c Fri Oct 28 11:17:30 2016 +0100 @@ -0,0 +1,591 @@ +/* mbed Microcontroller Library + * Copyright (c) 2013 Nordic Semiconductor + * + * 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 <stdbool.h> +#include "us_ticker_api.h" +#include "cmsis.h" +#include "PeripheralNames.h" +#include "nrf_delay.h" +#include "toolchain.h" + +/* + * Note: The micro-second timer API on the nRF51 platform is implemented using + * the RTC counter run at 32kHz (sourced from an external oscillator). This is + * a trade-off between precision and power. Running a normal 32-bit MCU counter + * at high frequency causes the average power consumption to rise to a few + * hundred micro-amps, which is prohibitive for typical low-power BLE + * applications. + * A 32kHz clock doesn't offer the precision needed for keeping u-second time, + * but we're assuming that this will not be a problem for the average user. + */ + +#define MAX_RTC_COUNTER_VAL 0x00FFFFFF /**< Maximum value of the RTC counter. */ +#define RTC_CLOCK_FREQ (uint32_t)(32768) +#define RTC1_IRQ_PRI 3 /**< Priority of the RTC1 interrupt (used + * for checking for timeouts and executing + * timeout handlers). This must be the same + * as APP_IRQ_PRIORITY_LOW; taken from the + * Nordic SDK. */ +#define MAX_RTC_TASKS_DELAY 47 /**< Maximum delay until an RTC task is executed. */ + +#define FUZZY_RTC_TICKS 2 /* RTC COMPARE occurs when a CC register is N and the RTC + * COUNTER value transitions from N-1 to N. If we're trying to + * setup a callback for a time which will arrive very shortly, + * there are limits to how short the callback interval may be for us + * to rely upon the RTC Compare trigger. If the COUNTER is N, + * writing N+2 to a CC register is guaranteed to trigger a COMPARE + * event at N+2. */ + +#define RTC_UNITS_TO_MICROSECONDS(RTC_UNITS) (((RTC_UNITS) * (uint64_t)1000000) / RTC_CLOCK_FREQ) +#define MICROSECONDS_TO_RTC_UNITS(MICROS) ((((uint64_t)(MICROS) * RTC_CLOCK_FREQ) + 999999) / 1000000) + +static bool us_ticker_inited = false; +static volatile uint32_t overflowCount; /**< The number of times the 24-bit RTC counter has overflowed. */ +static volatile bool us_ticker_callbackPending = false; +static uint32_t us_ticker_callbackTimestamp; +static bool os_tick_started = false; /**< flag indicating if the os_tick has started */ +/** + * The value previously set in the capture compare register of channel 1 + */ +static uint32_t previous_tick_cc_value = 0; + +/* + RTX provide the following definitions which are used by the tick code: + * os_trv: The number (minus 1) of clock cycle between two tick. + * os_clockrate: Time duration between two ticks (in us). + * OS_Tick_Handler: The function which handle a tick event. + This function is special because it never returns. + Those definitions are used by the code which handle the os tick. + To allow compilation of us_ticker programs without RTOS, those symbols are + exported from this module as weak ones. + */ +MBED_WEAK uint32_t const os_trv; +MBED_WEAK uint32_t const os_clockrate; +MBED_WEAK void OS_Tick_Handler() { } + +static inline void rtc1_enableCompareInterrupt(void) +{ + NRF_RTC1->EVTENCLR = RTC_EVTEN_COMPARE0_Msk; + NRF_RTC1->INTENSET = RTC_INTENSET_COMPARE0_Msk; +} + +static inline void rtc1_disableCompareInterrupt(void) +{ + NRF_RTC1->INTENCLR = RTC_INTENSET_COMPARE0_Msk; + NRF_RTC1->EVTENCLR = RTC_EVTEN_COMPARE0_Msk; +} + +static inline void rtc1_enableOverflowInterrupt(void) +{ + NRF_RTC1->EVTENCLR = RTC_EVTEN_OVRFLW_Msk; + NRF_RTC1->INTENSET = RTC_INTENSET_OVRFLW_Msk; +} + +static inline void rtc1_disableOverflowInterrupt(void) +{ + NRF_RTC1->INTENCLR = RTC_INTENSET_OVRFLW_Msk; + NRF_RTC1->EVTENCLR = RTC_EVTEN_OVRFLW_Msk; +} + +static inline void invokeCallback(void) +{ + us_ticker_callbackPending = false; + rtc1_disableCompareInterrupt(); + us_ticker_irq_handler(); +} + +/** + * @brief Function for starting the RTC1 timer. The RTC timer is expected to + * keep running--some interrupts may be disabled temporarily. + */ +static void rtc1_start() +{ + NRF_RTC1->PRESCALER = 0; /* for no pre-scaling. */ + + rtc1_enableOverflowInterrupt(); + + NVIC_SetPriority(RTC1_IRQn, RTC1_IRQ_PRI); + NVIC_ClearPendingIRQ(RTC1_IRQn); + NVIC_EnableIRQ(RTC1_IRQn); + + NRF_RTC1->TASKS_START = 1; + nrf_delay_us(MAX_RTC_TASKS_DELAY); +} + +/** + * @brief Function for stopping the RTC1 timer. We don't expect to call this. + */ +void rtc1_stop(void) +{ + // If the os tick has been started, RTC1 shouldn't be stopped + // In that case, us ticker and overflow interrupt are disabled. + if (os_tick_started) { + rtc1_disableCompareInterrupt(); + rtc1_disableOverflowInterrupt(); + } else { + NVIC_DisableIRQ(RTC1_IRQn); + rtc1_disableCompareInterrupt(); + rtc1_disableOverflowInterrupt(); + + NRF_RTC1->TASKS_STOP = 1; + nrf_delay_us(MAX_RTC_TASKS_DELAY); + + NRF_RTC1->TASKS_CLEAR = 1; + nrf_delay_us(MAX_RTC_TASKS_DELAY); + } +} + +/** + * @brief Function for returning the current value of the RTC1 counter. + * + * @return Current RTC1 counter as a 64-bit value with 56-bit precision (even + * though the underlying counter is 24-bit) + */ +static inline uint64_t rtc1_getCounter64(void) +{ + if (NRF_RTC1->EVENTS_OVRFLW) { + overflowCount++; + NRF_RTC1->EVENTS_OVRFLW = 0; + NRF_RTC1->EVTENCLR = RTC_EVTEN_OVRFLW_Msk; + } + return ((uint64_t)overflowCount << 24) | NRF_RTC1->COUNTER; +} + +/** + * @brief Function for returning the current value of the RTC1 counter. + * + * @return Current RTC1 counter as a 32-bit value (even though the underlying counter is 24-bit) + */ +static inline uint32_t rtc1_getCounter(void) +{ + return rtc1_getCounter64(); +} + +/** + * @brief Function for handling the RTC1 interrupt for us ticker (capture compare channel 0 and overflow). + * + * @details Checks for timeouts, and executes timeout handlers for expired timers. + */ +void us_ticker_handler(void) +{ + if (NRF_RTC1->EVENTS_OVRFLW) { + overflowCount++; + NRF_RTC1->EVENTS_OVRFLW = 0; + NRF_RTC1->EVTENCLR = RTC_EVTEN_OVRFLW_Msk; + } + if (NRF_RTC1->EVENTS_COMPARE[0]) { + NRF_RTC1->EVENTS_COMPARE[0] = 0; + NRF_RTC1->EVTENCLR = RTC_EVTEN_COMPARE0_Msk; + if (us_ticker_callbackPending && ((int)(us_ticker_callbackTimestamp - rtc1_getCounter()) <= 0)) + invokeCallback(); + } +} + +void us_ticker_init(void) +{ + if (us_ticker_inited) { + return; + } + + rtc1_start(); + us_ticker_inited = true; +} + +uint32_t us_ticker_read() +{ + if (!us_ticker_inited) { + us_ticker_init(); + } + + /* Return a pseudo microsecond counter value. This is only as precise as the + * 32khz low-freq clock source, but could be adequate.*/ + return RTC_UNITS_TO_MICROSECONDS(rtc1_getCounter64()); +} + +/** + * Setup the us_ticker callback interrupt to go at the given timestamp. + * + * @Note: Only one callback is pending at any time. + * + * @Note: If a callback is pending, and this function is called again, the new + * callback-time overrides the existing callback setting. It is the caller's + * responsibility to ensure that this function is called to setup a callback for + * the earliest timeout. + * + * @Note: If this function is used to setup an interrupt which is immediately + * pending--such as for 'now' or a time in the past,--then the callback is + * invoked a few ticks later. + */ +void us_ticker_set_interrupt(timestamp_t timestamp) +{ + if (!us_ticker_inited) { + us_ticker_init(); + } + + /* + * The argument to this function is a 32-bit microsecond timestamp for when + * a callback should be invoked. On the nRF51, we use an RTC timer running + * at 32kHz to implement a low-power us-ticker. This results in a problem + * based on the fact that 1000000 is not a multiple of 32768. + * + * Going from a micro-second based timestamp to a 32kHz based RTC-time is a + * linear mapping; but this mapping doesn't preserve wraparounds--i.e. when + * the 32-bit micro-second timestamp wraps around unfortunately the + * underlying RTC counter doesn't. The result is that timestamp expiry + * checks on micro-second timestamps don't yield the same result when + * applied on the corresponding RTC timestamp values. + * + * One solution is to translate the incoming 32-bit timestamp into a virtual + * 64-bit timestamp based on the knowledge of system-uptime, and then use + * this wraparound-free 64-bit value to do a linear mapping to RTC time. + * System uptime on an nRF is maintained using the 24-bit RTC counter. We + * track the overflow count to extend the 24-bit hardware counter by an + * additional 32 bits. RTC_UNITS_TO_MICROSECONDS() converts this into + * microsecond units (in 64-bits). + */ + const uint64_t currentTime64 = RTC_UNITS_TO_MICROSECONDS(rtc1_getCounter64()); + uint64_t timestamp64 = (currentTime64 & ~(uint64_t)0xFFFFFFFFULL) + timestamp; + if (((uint32_t)currentTime64 > 0x80000000) && (timestamp < 0x80000000)) { + timestamp64 += (uint64_t)0x100000000ULL; + } + uint32_t newCallbackTime = MICROSECONDS_TO_RTC_UNITS(timestamp64); + + /* Check for repeat setup of an existing callback. This is actually not + * important; the following code should work even without this check. */ + if (us_ticker_callbackPending && (newCallbackTime == us_ticker_callbackTimestamp)) { + return; + } + + /* Check for callbacks which are immediately (or will *very* shortly become) pending. + * Even if they are immediately pending, they are scheduled to trigger a few + * ticks later. This keeps things simple by invoking the callback from an + * independent interrupt context. */ + if ((int)(newCallbackTime - rtc1_getCounter()) <= (int)FUZZY_RTC_TICKS) { + newCallbackTime = rtc1_getCounter() + FUZZY_RTC_TICKS; + } + + NRF_RTC1->CC[0] = newCallbackTime & MAX_RTC_COUNTER_VAL; + us_ticker_callbackTimestamp = newCallbackTime; + if (!us_ticker_callbackPending) { + us_ticker_callbackPending = true; + rtc1_enableCompareInterrupt(); + } +} + +void us_ticker_disable_interrupt(void) +{ + if (us_ticker_callbackPending) { + rtc1_disableCompareInterrupt(); + us_ticker_callbackPending = false; + } +} + +void us_ticker_clear_interrupt(void) +{ + NRF_RTC1->EVENTS_OVRFLW = 0; + NRF_RTC1->EVENTS_COMPARE[0] = 0; +} + + +#if defined (__CC_ARM) /* ARMCC Compiler */ + +__asm void RTC1_IRQHandler(void) +{ + IMPORT OS_Tick_Handler + IMPORT us_ticker_handler + + /** + * Chanel 1 of RTC1 is used by RTX as a systick. + * If the compare event on channel 1 is set, then branch to OS_Tick_Handler. + * Otherwise, just execute us_ticker_handler. + * This function has to be written in assembly and tagged as naked because OS_Tick_Handler + * will never return. + * A c function would put lr on the stack before calling OS_Tick_Handler and this value + * would never been dequeued. + * + * \code + * void RTC1_IRQHandler(void) { + if(NRF_RTC1->EVENTS_COMPARE[1]) { + // never return... + OS_Tick_Handler(); + } else { + us_ticker_handler(); + } + } + * \endcode + */ + ldr r0,=0x40011144 + ldr r1, [r0, #0] + cmp r1, #0 + beq US_TICKER_HANDLER + bl OS_Tick_Handler +US_TICKER_HANDLER + push {r3, lr} + bl us_ticker_handler + pop {r3, pc} + nop /* padding */ +} + +#elif defined (__GNUC__) /* GNU Compiler */ + +__attribute__((naked)) void RTC1_IRQHandler(void) +{ + /** + * Chanel 1 of RTC1 is used by RTX as a systick. + * If the compare event on channel 1 is set, then branch to OS_Tick_Handler. + * Otherwise, just execute us_ticker_handler. + * This function has to be written in assembly and tagged as naked because OS_Tick_Handler + * will never return. + * A c function would put lr on the stack before calling OS_Tick_Handler and this value + * would never been dequeued. + * + * \code + * void RTC1_IRQHandler(void) { + if(NRF_RTC1->EVENTS_COMPARE[1]) { + // never return... + OS_Tick_Handler(); + } else { + us_ticker_handler(); + } + } + * \endcode + */ + __asm__ ( + "ldr r0,=0x40011144\n" + "ldr r1, [r0, #0]\n" + "cmp r1, #0\n" + "beq US_TICKER_HANDLER\n" + "bl OS_Tick_Handler\n" + "US_TICKER_HANDLER:\n" + "push {r3, lr}\n" + "bl us_ticker_handler\n" + "pop {r3, pc}\n" + "nop" + ); +} + +#else + +#error Compiler not supported. +#error Provide a definition of RTC1_IRQHandler. + +/* + * Chanel 1 of RTC1 is used by RTX as a systick. + * If the compare event on channel 1 is set, then branch to OS_Tick_Handler. + * Otherwise, just execute us_ticker_handler. + * This function has to be written in assembly and tagged as naked because OS_Tick_Handler + * will never return. + * A c function would put lr on the stack before calling OS_Tick_Handler and this value + * will never been dequeued. After a certain time a stack overflow will happen. + * + * \code + * void RTC1_IRQHandler(void) { + if(NRF_RTC1->EVENTS_COMPARE[1]) { + // never return... + OS_Tick_Handler(); + } else { + us_ticker_handler(); + } + } + * \endcode + */ + +#endif + +/** + * Return the next number of clock cycle needed for the next tick. + * @note This function has been carrefuly optimized for a systick occuring every 1000us. + */ +static uint32_t get_next_tick_cc_delta() { + uint32_t delta = 0; + + if (os_clockrate != 1000) { + // In RTX, by default SYSTICK is is used. + // A tick event is generated every os_trv + 1 clock cycles of the system timer. + delta = os_trv + 1; + } else { + // If the clockrate is set to 1000us then 1000 tick should happen every second. + // Unfortunatelly, when clockrate is set to 1000, os_trv is equal to 31. + // If (os_trv + 1) is used as the delta value between two ticks, 1000 ticks will be + // generated in 32000 clock cycle instead of 32768 clock cycles. + // As a result, if a user schedule an OS timer to start in 100s, the timer will start + // instead after 97.656s + // The code below fix this issue, a clock rate of 1000s will generate 1000 ticks in 32768 + // clock cycles. + // The strategy is simple, for 1000 ticks: + // * 768 ticks will occur 33 clock cycles after the previous tick + // * 232 ticks will occur 32 clock cycles after the previous tick + // By default every delta is equal to 33. + // Every five ticks (20%, 200 delta in one second), the delta is equal to 32 + // The remaining (32) deltas equal to 32 are distributed using primes numbers. + static uint32_t counter = 0; + if ((counter % 5) == 0 || (counter % 31) == 0 || (counter % 139) == 0 || (counter == 503)) { + delta = 32; + } else { + delta = 33; + } + ++counter; + if (counter == 1000) { + counter = 0; + } + } + return delta; +} + +static inline void clear_tick_interrupt() { + NRF_RTC1->EVENTS_COMPARE[1] = 0; + NRF_RTC1->EVTENCLR = (1 << 17); +} + +/** + * Indicate if a value is included in a range which can be wrapped. + * @param begin start of the range + * @param end end of the range + * @param val value to check + * @return true if the value is included in the range and false otherwise. + */ +static inline bool is_in_wrapped_range(uint32_t begin, uint32_t end, uint32_t val) { + // regular case, begin < end + // return true if begin <= val < end + if (begin < end) { + if (begin <= val && val < end) { + return true; + } else { + return false; + } + } else { + // In this case end < begin because it has wrap around the limits + // return false if end < val < begin + if (end < val && val < begin) { + return false; + } else { + return true; + } + } + +} + +/** + * Register the next tick. + */ +static void register_next_tick() { + previous_tick_cc_value = NRF_RTC1->CC[1]; + uint32_t delta = get_next_tick_cc_delta(); + uint32_t new_compare_value = (previous_tick_cc_value + delta) & MAX_RTC_COUNTER_VAL; + + // Disable irq directly for few cycles, + // Validation of the new CC value against the COUNTER, + // Setting the new CC value and enabling CC IRQ should be an atomic operation + // Otherwise, there is a possibility to set an invalid CC value because + // the RTC1 keeps running. + // This code is very short 20-38 cycles in the worst case, it shouldn't + // disturb softdevice. + __disable_irq(); + uint32_t current_counter = NRF_RTC1->COUNTER; + + // If an overflow occur, set the next tick in COUNTER + delta clock cycles + if (is_in_wrapped_range(previous_tick_cc_value, new_compare_value, current_counter) == false) { + new_compare_value = current_counter + delta; + } + NRF_RTC1->CC[1] = new_compare_value; + + // set the interrupt of CC channel 1 and reenable IRQs + NRF_RTC1->INTENSET = RTC_INTENSET_COMPARE1_Msk; + __enable_irq(); +} + +/** + * Initialize alternative hardware timer as RTX kernel timer + * This function is directly called by RTX. + * @note this function shouldn't be called directly. + * @return IRQ number of the alternative hardware timer + */ +int os_tick_init (void) +{ + // their is no need to start the LF clock, it is already started by SystemInit. + NVIC_SetPriority(RTC1_IRQn, RTC1_IRQ_PRI); + NVIC_ClearPendingIRQ(RTC1_IRQn); + NVIC_EnableIRQ(RTC1_IRQn); + + NRF_RTC1->TASKS_START = 1; + nrf_delay_us(MAX_RTC_TASKS_DELAY); + + NRF_RTC1->CC[1] = 0; + clear_tick_interrupt(); + register_next_tick(); + + os_tick_started = true; + + return RTC1_IRQn; +} + +/** + * Acknowledge the tick interrupt. + * This function is called by the function OS_Tick_Handler of RTX. + * @note this function shouldn't be called directly. + */ +void os_tick_irqack(void) +{ + clear_tick_interrupt(); + register_next_tick(); +} + +/** + * Returns the overflow flag of the alternative hardware timer. + * @note This function is exposed by RTX kernel. + * @return 1 if the timer has overflowed and 0 otherwise. + */ +uint32_t os_tick_ovf(void) { + uint32_t current_counter = NRF_RTC1->COUNTER; + uint32_t next_tick_cc_value = NRF_RTC1->CC[1]; + + return is_in_wrapped_range(previous_tick_cc_value, next_tick_cc_value, current_counter) ? 0 : 1; +} + +/** + * Return the value of the alternative hardware timer. + * @note The documentation is not very clear about what is expected as a result, + * is it an ascending counter, a descending one ? + * None of this is specified. + * The default systick is a descending counter and this function return values in + * descending order, even if the internal counter used is an ascending one. + * @return the value of the alternative hardware timer. + */ +uint32_t os_tick_val(void) { + uint32_t current_counter = NRF_RTC1->COUNTER; + uint32_t next_tick_cc_value = NRF_RTC1->CC[1]; + + // do not use os_tick_ovf because its counter value can be different + if(is_in_wrapped_range(previous_tick_cc_value, next_tick_cc_value, current_counter)) { + if (next_tick_cc_value > previous_tick_cc_value) { + return next_tick_cc_value - current_counter; + } else if(current_counter <= next_tick_cc_value) { + return next_tick_cc_value - current_counter; + } else { + return next_tick_cc_value + (MAX_RTC_COUNTER_VAL - current_counter); + } + } else { + // use (os_trv + 1) has the base step, can be totally inacurate ... + uint32_t clock_cycles_by_tick = os_trv + 1; + + // if current counter has wrap arround, add the limit to it. + if (current_counter < next_tick_cc_value) { + current_counter = current_counter + MAX_RTC_COUNTER_VAL; + } + + return clock_cycles_by_tick - ((current_counter - next_tick_cc_value) % clock_cycles_by_tick); + } +}