diff --git a/ports/atmel-samd/common-hal/frequencyio/FrequencyIn.c b/ports/atmel-samd/common-hal/frequencyio/FrequencyIn.c
new file mode 100644
index 0000000000..e499684288
--- /dev/null
+++ b/ports/atmel-samd/common-hal/frequencyio/FrequencyIn.c
@@ -0,0 +1,545 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Michael Schroeder
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdint.h>
+
+#include "hal/include/hal_gpio.h"
+#include "atmel_start_pins.h"
+#include "supervisor/shared/translate.h"
+
+#include "mpconfigport.h"
+#include "py/runtime.h"
+#include "timer_handler.h"
+#include "background.h"
+
+#include "samd/clocks.h"
+#include "samd/timers.h"
+#include "samd/events.h"
+#include "samd/pins.h"
+#include "samd/external_interrupts.h"
+
+#include "shared-bindings/frequencyio/FrequencyIn.h"
+#include "peripheral_clk_config.h"
+#include "hpl_gclk_config.h"
+
+#include "tick.h"
+
+#ifdef SAMD21
+#include "hpl/gclk/hpl_gclk_base.h"
+#endif
+
+static frequencyio_frequencyin_obj_t *active_frequencyins[TC_INST_NUM];
+volatile uint8_t reference_tc = 0xff;
+#ifdef SAMD51
+static uint8_t dpll_gclk;
+#endif
+
+void frequencyin_emergency_cancel_capture(uint8_t index) {
+    frequencyio_frequencyin_obj_t* self = active_frequencyins[index];
+
+    NVIC_DisableIRQ(self->TC_IRQ);
+    NVIC_ClearPendingIRQ(self->TC_IRQ);
+    #ifdef SAMD21
+    NVIC_DisableIRQ(EIC_IRQn);
+    NVIC_ClearPendingIRQ(EIC_IRQn);
+    #endif
+    #ifdef SAMD51
+    NVIC_DisableIRQ(EIC_0_IRQn + self->channel);
+    NVIC_ClearPendingIRQ(EIC_0_IRQn + self->channel);
+    #endif
+
+    common_hal_frequencyio_frequencyin_pause(self); // pause any further captures
+
+    NVIC_EnableIRQ(self->TC_IRQ);
+    #ifdef SAMD21
+    NVIC_EnableIRQ(EIC_IRQn);
+    #endif
+    #ifdef SAMD51
+    NVIC_EnableIRQ(EIC_0_IRQn + self->channel);
+    #endif
+    mp_raise_RuntimeError(translate("Frequency captured is above capability. Capture Paused."));
+}
+
+void frequencyin_interrupt_handler(uint8_t index) {
+    Tc* ref_tc = tc_insts[reference_tc];
+
+    if (!ref_tc->COUNT16.INTFLAG.bit.OVF) return; // false trigger
+
+    uint32_t current_us;
+    uint64_t current_ms;
+    current_tick(&current_ms, &current_us);
+
+    for (uint8_t i = 0; i <= (TC_INST_NUM - 1); i++) {
+        if (active_frequencyins[i] != NULL) {
+            frequencyio_frequencyin_obj_t* self = active_frequencyins[i];
+            Tc* tc = tc_insts[self->tc_index];
+
+            uint32_t mask = 1 << self->channel;
+            if ((EIC->INTFLAG.reg & mask) == mask) {
+                // Make sure capture_period has elapsed before we
+                // record a new event count.
+                if (current_ms - self->last_ms >= self->capture_period) {
+                    float new_factor = self->last_us + (1000 - current_us);
+                    self->factor = (current_ms - self->last_ms) + (new_factor / 1000);
+                    self->last_ms = current_ms;
+                    self->last_us = current_us;
+
+                    #ifdef SAMD51
+                    tc->COUNT16.CTRLBSET.bit.CMD = TC_CTRLBSET_CMD_READSYNC_Val;
+                    while ((tc->COUNT16.SYNCBUSY.bit.COUNT == 1) ||
+                           (tc->COUNT16.CTRLBSET.bit.CMD == TC_CTRLBSET_CMD_READSYNC_Val)) {
+                    }
+                    #endif
+
+                    uint16_t new_freq = tc->COUNT16.COUNT.reg;
+                    if ((tc->COUNT16.INTFLAG.reg & TC_INTFLAG_OVF) == 1) {
+                        new_freq += 65535;
+                        tc->COUNT16.INTFLAG.reg |= TC_INTFLAG_OVF;
+                    }
+                    self->frequency = new_freq;
+
+                    #ifdef SAMD51
+                    tc->COUNT16.CTRLBSET.bit.CMD = TC_CTRLBSET_CMD_RETRIGGER_Val;
+                    while ((tc->COUNT16.SYNCBUSY.bit.COUNT == 1) ||
+                           (tc->COUNT16.CTRLBSET.bit.CMD == TC_CTRLBSET_CMD_RETRIGGER_Val)) {
+                    }
+                    #endif
+                }
+                EIC->INTFLAG.reg |= mask;
+            }
+
+            // Check if we've reached the upper limit of detection
+            if (!background_tasks_ok() || self->errored_too_fast) {
+                self->errored_too_fast = true;
+                frequencyin_emergency_cancel_capture(i);
+            }
+        }
+    }
+    ref_tc->COUNT16.INTFLAG.reg |= TC_INTFLAG_OVF;
+}
+
+void frequencyin_reference_tc_init() {
+    if (reference_tc == 0xff) {
+        return;
+    }
+    #ifdef SAMD21
+    turn_on_clocks(true, reference_tc, 0, TC_HANDLER_FREQUENCYIN);
+    #endif
+    // use the DPLL we setup so that the reference_tc and freqin_tc(s)
+    // are using the same clock frequency.
+    #ifdef SAMD51
+    if (dpll_gclk == 0xff) {
+        frequencyin_samd51_start_dpll();
+    }
+    turn_on_clocks(true, reference_tc, dpll_gclk, TC_HANDLER_FREQUENCYIN);
+    #endif
+
+    Tc *tc = tc_insts[reference_tc];
+    tc_set_enable(tc, false);
+    tc_reset(tc);
+
+    #ifdef SAMD21
+    tc->COUNT16.CTRLA.reg = TC_CTRLA_MODE_COUNT16 | TC_CTRLA_PRESCALER_DIV1;
+    tc->COUNT16.INTENSET.bit.OVF = 1;
+    NVIC_EnableIRQ(TC3_IRQn + reference_tc);
+    #endif
+    #ifdef SAMD51
+    tc->COUNT16.CTRLA.reg = TC_CTRLA_MODE_COUNT16 |
+                            TC_CTRLA_PRESCALER_DIV1;
+    tc->COUNT16.INTENSET.bit.OVF = 1;
+    NVIC_EnableIRQ(TC0_IRQn + reference_tc);
+    #endif
+}
+
+bool frequencyin_reference_tc_enabled() {
+    if (reference_tc == 0xff) {
+        return false;
+    }
+    Tc *tc = tc_insts[reference_tc];
+    return tc->COUNT16.CTRLA.bit.ENABLE;
+}
+
+void frequencyin_reference_tc_enable(bool enable) {
+    if (reference_tc == 0xff) {
+        return;
+    }
+    Tc *tc = tc_insts[reference_tc];
+    tc_set_enable(tc, enable);
+}
+
+#ifdef SAMD51
+void frequencyin_samd51_start_dpll() {
+    if (clock_get_enabled(0, GCLK_SOURCE_DPLL1)) {
+        return;
+    }
+
+    uint8_t free_gclk = find_free_gclk(1);
+    if (free_gclk == 0xff) {
+        dpll_gclk = 0xff;
+        return;
+    }
+
+    GCLK->PCHCTRL[OSCCTRL_GCLK_ID_FDPLL1].reg = GCLK_PCHCTRL_CHEN | GCLK_PCHCTRL_GEN(free_gclk);
+    // TC4-7 can only have a max of 100MHz source
+    // DPLL1 frequency equation with [X]OSC32K as source: 98.304MHz = 32768(2999 + 1 + 0/32)
+    // Will also enable the Lock Bypass due to low-frequency sources causing DPLL unlocks
+    // as outlined in the Errata (1.12.1)
+    OSCCTRL->Dpll[1].DPLLRATIO.reg = OSCCTRL_DPLLRATIO_LDRFRAC(0) | OSCCTRL_DPLLRATIO_LDR(2999);
+    if (board_has_crystal()) { // we can use XOSC32K directly as the source
+        OSC32KCTRL->XOSC32K.bit.EN32K = 1;
+        OSCCTRL->Dpll[1].DPLLCTRLB.reg = OSCCTRL_DPLLCTRLB_REFCLK(1) |
+                                         OSCCTRL_DPLLCTRLB_LBYPASS;
+    } else {
+        // can't use OSCULP32K directly; need to setup a GCLK as a reference,
+        // which must be done in samd/clocks.c to avoid waiting for sync
+        return;
+        //OSC32KCTRL->OSCULP32K.bit.EN32K = 1;
+        //OSCCTRL->Dpll[1].DPLLCTRLB.reg = OSCCTRL_DPLLCTRLB_REFCLK(0);
+    }
+    OSCCTRL->Dpll[1].DPLLCTRLA.reg = OSCCTRL_DPLLCTRLA_ENABLE;
+
+    while (!(OSCCTRL->Dpll[1].DPLLSTATUS.bit.LOCK || OSCCTRL->Dpll[1].DPLLSTATUS.bit.CLKRDY)) {}
+    enable_clock_generator(free_gclk, GCLK_GENCTRL_SRC_DPLL1_Val, 1);
+    dpll_gclk = free_gclk;
+}
+
+void frequencyin_samd51_stop_dpll() {
+    if (!clock_get_enabled(0, GCLK_SOURCE_DPLL1)) {
+        return;
+    }
+
+    disable_clock_generator(dpll_gclk);
+
+    GCLK->PCHCTRL[OSCCTRL_GCLK_ID_FDPLL1].reg = 0;
+    OSCCTRL->Dpll[1].DPLLCTRLA.reg = 0;
+    OSCCTRL->Dpll[1].DPLLRATIO.reg = 0;
+    OSCCTRL->Dpll[1].DPLLCTRLB.reg = 0;
+
+    while (OSCCTRL->Dpll[1].DPLLSYNCBUSY.bit.ENABLE) {
+    }
+    dpll_gclk = 0xff;
+}
+#endif
+
+void common_hal_frequencyio_frequencyin_construct(frequencyio_frequencyin_obj_t* self, const mcu_pin_obj_t* pin, const uint16_t capture_period) {
+
+    if (!pin->has_extint) {
+        mp_raise_RuntimeError(translate("No hardware support on pin"));
+    }
+    if ((capture_period == 0) || (capture_period > 500)) {
+        // TODO: find a sutiable message that is already translated
+        mp_raise_ValueError(translate("Invalid something"));
+    }
+    uint32_t mask = 1 << pin->extint_channel;
+    if (eic_get_enable() == 1 &&
+    #ifdef SAMD21
+    ((EIC->INTENSET.vec.EXTINT & mask) != 0 || (EIC->EVCTRL.vec.EXTINTEO & mask) != 0)) {
+    #endif
+    #ifdef SAMD51
+    ((EIC->INTENSET.bit.EXTINT & mask) != 0 || (EIC->EVCTRL.bit.EXTINTEO & mask) != 0)) {
+    #endif
+        mp_raise_RuntimeError(translate("EXTINT channel already in use"));
+    }
+
+    uint8_t timer_index = find_free_timer();
+    if (timer_index == 0xff) {
+        mp_raise_RuntimeError(translate("All timers in use"));
+    }
+    Tc *tc = tc_insts[timer_index];
+
+    self->tc_index = timer_index;
+    self->pin = pin->number;
+    self->channel = pin->extint_channel;
+    self->errored_too_fast = false;
+    self->last_ms = 0;
+    self->last_us = 1000;
+    self->capture_period = capture_period;
+    #ifdef SAMD21
+    self->TC_IRQ = TC3_IRQn + timer_index;
+    #endif
+    #ifdef SAMD51
+    self->TC_IRQ = TC0_IRQn + timer_index;
+    #endif
+
+    active_frequencyins[timer_index] = self;
+
+    // SAMD21: We use GCLK0 generated from DFLL running at 48mhz
+    // SAMD51: We use a GCLK generated from DPLL1 running at <100mhz
+    #ifdef SAMD21
+    turn_on_clocks(true, timer_index, 0, TC_HANDLER_NO_INTERRUPT);
+    #endif
+    #ifdef SAMD51
+    frequencyin_samd51_start_dpll();
+    if (dpll_gclk == 0xff && !clock_get_enabled(0, GCLK_SOURCE_DPLL1)) {
+        common_hal_frequencyio_frequencyin_deinit(self);
+        mp_raise_RuntimeError(translate("No available clocks"));
+    }
+    turn_on_clocks(true, timer_index, dpll_gclk, TC_HANDLER_NO_INTERRUPT);
+    #endif
+
+    // Ensure EIC is on
+    if (eic_get_enable() == 0) {
+        turn_on_external_interrupt_controller(); // enables EIC, so disable it after
+    }
+    eic_set_enable(false);
+
+    uint8_t sense_setting = EIC_CONFIG_SENSE0_HIGH_Val;
+    uint8_t config_index = self->channel / 8;
+    uint8_t position = (self->channel % 8) * 4;
+    uint32_t masked_value = EIC->CONFIG[config_index].reg & ~(0xf << position);
+    EIC->CONFIG[config_index].reg = masked_value | (sense_setting << position);
+
+    #ifdef SAMD21
+    masked_value = EIC->EVCTRL.vec.EXTINTEO;
+    EIC->EVCTRL.vec.EXTINTEO = masked_value | (1 << self->channel);
+    #endif
+    #ifdef SAMD51
+    masked_value = EIC->EVCTRL.bit.EXTINTEO;
+    EIC->EVCTRL.bit.EXTINTEO = masked_value | (1 << self->channel);
+    EIC->ASYNCH.bit.ASYNCH = 1;
+    #endif
+
+    turn_on_cpu_interrupt(self->channel);
+
+    eic_set_enable(true);
+
+    // Turn on EVSYS
+    turn_on_event_system();
+    uint8_t evsys_channel = find_async_event_channel();
+    #ifdef SAMD21
+    connect_event_user_to_channel((EVSYS_ID_USER_TC3_EVU + timer_index), evsys_channel);
+    #endif
+    #ifdef SAMD51
+    connect_event_user_to_channel((EVSYS_ID_USER_TC0_EVU + timer_index), evsys_channel);
+    #endif
+    init_async_event_channel(evsys_channel, (EVSYS_ID_GEN_EIC_EXTINT_0 + self->channel));
+    self->event_channel = evsys_channel;
+
+    tc_set_enable(tc, false);
+    tc_reset(tc);
+    #ifdef SAMD21
+    tc->COUNT16.CTRLA.reg = TC_CTRLA_MODE_COUNT16 |
+                            TC_CTRLA_PRESCALER_DIV1;
+    tc->COUNT16.EVCTRL.bit.TCEI = 1;
+    tc->COUNT16.EVCTRL.bit.EVACT = TC_EVCTRL_EVACT_COUNT_Val;
+    #endif
+
+    #ifdef SAMD51
+    tc->COUNT16.EVCTRL.reg = TC_EVCTRL_EVACT(TC_EVCTRL_EVACT_COUNT_Val) | TC_EVCTRL_TCEI;
+    tc->COUNT16.CTRLA.reg = TC_CTRLA_MODE_COUNT16 |
+                            TC_CTRLA_PRESCALER_DIV1;
+    #endif
+
+    NVIC_EnableIRQ(self->TC_IRQ);
+
+    gpio_set_pin_function(pin->number, GPIO_PIN_FUNCTION_A);
+
+    tc_set_enable(tc, true);
+
+    // setup reference TC if not already
+    if (reference_tc == 0xff) {
+        reference_tc = find_free_timer();
+        if (reference_tc == 0xff) {
+            common_hal_frequencyio_frequencyin_deinit(self);
+            mp_raise_RuntimeError(translate("All timers in use"));
+        }
+        frequencyin_reference_tc_init();
+    }
+    if (!frequencyin_reference_tc_enabled()) {
+        frequencyin_reference_tc_enable(true);
+    }
+}
+
+bool common_hal_frequencyio_frequencyin_deinited(frequencyio_frequencyin_obj_t* self) {
+    return self->pin == NO_PIN;
+}
+
+void common_hal_frequencyio_frequencyin_deinit(frequencyio_frequencyin_obj_t* self) {
+    if (common_hal_frequencyio_frequencyin_deinited(self)) {
+        return;
+    }
+    reset_pin(self->pin);
+
+    // turn off EIC & EVSYS utilized by this TC
+    disable_event_channel(self->event_channel);
+    eic_set_enable(false);
+    #ifdef SAMD21
+    disable_event_user(EVSYS_ID_USER_TC3_EVU + self->tc_index);
+    uint32_t masked_value = EIC->EVCTRL.vec.EXTINTEO;
+    EIC->EVCTRL.vec.EXTINTEO = masked_value ^ (1 << self->channel);
+    #endif
+    #ifdef SAMD51
+    disable_event_user(EVSYS_ID_USER_TC0_EVU + self->tc_index);
+    uint32_t masked_value = EIC->EVCTRL.bit.EXTINTEO;
+    EIC->EVCTRL.bit.EXTINTEO = masked_value ^ (1 << self->channel);
+    NVIC_DisableIRQ(EIC_0_IRQn + self->channel);
+    NVIC_ClearPendingIRQ(EIC_0_IRQn + self->channel);
+    #endif
+    eic_set_enable(true);
+    // check if any other objects are using the EIC; if not, turn it off
+    if (EIC->EVCTRL.reg == 0 && EIC->INTENSET.reg == 0) {
+        eic_reset();
+        turn_off_external_interrupt_controller();
+    }
+
+    // turn off the TC we were using
+    Tc *tc = tc_insts[self->tc_index];
+    tc_set_enable(tc, false);
+    tc_reset(tc);
+    NVIC_DisableIRQ(self->TC_IRQ);
+    NVIC_ClearPendingIRQ(self->TC_IRQ);
+
+    active_frequencyins[self->tc_index] = NULL;
+    self->tc_index = 0xff;
+    self->pin = NO_PIN;
+
+    bool check_active = false;
+    for (uint8_t i = 0; i <= (TC_INST_NUM - 1); i++) {
+        if (active_frequencyins[i] != NULL) {
+            check_active = true;
+        }
+    }
+    if (!check_active) {
+        frequencyin_reference_tc_enable(false);
+        reference_tc = 0xff;
+        #ifdef SAMD51
+        frequencyin_samd51_stop_dpll();
+        #endif
+    }
+}
+
+uint32_t common_hal_frequencyio_frequencyin_get_item(frequencyio_frequencyin_obj_t* self) {
+    NVIC_DisableIRQ(self->TC_IRQ);
+    #ifdef SAMD21
+    NVIC_DisableIRQ(EIC_IRQn);
+    #endif
+    #ifdef SAMD51
+    NVIC_DisableIRQ(EIC_0_IRQn + self->channel);
+    #endif
+
+    // adjust for actual capture period vs base `capture_period`
+    float frequency_adjustment = 0.0;
+    if (self->factor > self->capture_period) {
+        float time_each_event = self->factor / self->frequency; // get the time for each event during actual period
+        float capture_diff = self->factor - self->capture_period; // get the difference of actual and base periods
+        // we only need to adjust if the capture_diff can contain 1 or more events
+        // if so, we add how many events could have occured during the diff time
+        if (time_each_event > capture_diff) {
+            frequency_adjustment = capture_diff / time_each_event;
+        }
+    }
+
+    float value = 1000 / (self->capture_period / (self->frequency + frequency_adjustment));
+
+    NVIC_ClearPendingIRQ(self->TC_IRQ);
+    NVIC_EnableIRQ(self->TC_IRQ);
+    #ifdef SAMD21
+    NVIC_ClearPendingIRQ(EIC_IRQn);
+    NVIC_EnableIRQ(EIC_IRQn);
+    #endif
+    #ifdef SAMD51
+    NVIC_ClearPendingIRQ(EIC_0_IRQn + self->channel);
+    NVIC_EnableIRQ(EIC_0_IRQn + self->channel);
+    #endif
+
+    return value;
+}
+
+void common_hal_frequencyio_frequencyin_pause(frequencyio_frequencyin_obj_t* self) {
+    Tc *tc = tc_insts[self->tc_index];
+    if (!tc->COUNT16.EVCTRL.bit.TCEI) {
+        return;
+    }
+    tc->COUNT16.EVCTRL.bit.TCEI = 0;
+
+    #ifdef SAMD21
+    uint32_t masked_value = EIC->EVCTRL.vec.EXTINTEO;
+    EIC->EVCTRL.vec.EXTINTEO = masked_value | (0 << self->channel);
+    #endif
+    #ifdef SAMD51
+    uint32_t masked_value = EIC->EVCTRL.bit.EXTINTEO;
+    EIC->EVCTRL.bit.EXTINTEO = masked_value | (0 << self->channel);
+    #endif
+    return;
+}
+
+void common_hal_frequencyio_frequencyin_resume(frequencyio_frequencyin_obj_t* self) {
+    Tc *tc = tc_insts[self->tc_index];
+    if (tc->COUNT16.EVCTRL.bit.TCEI) {
+        return;
+    }
+    tc->COUNT16.EVCTRL.bit.TCEI = 1;
+
+    #ifdef SAMD21
+    uint32_t masked_value = EIC->EVCTRL.vec.EXTINTEO;
+    EIC->EVCTRL.vec.EXTINTEO = masked_value | (1 << self->channel);
+    #endif
+    #ifdef SAMD51
+    uint32_t masked_value = EIC->EVCTRL.bit.EXTINTEO;
+    EIC->EVCTRL.bit.EXTINTEO = masked_value | (1 << self->channel);
+    #endif
+    self->errored_too_fast = false;
+    return;
+}
+
+void common_hal_frequencyio_frequencyin_clear(frequencyio_frequencyin_obj_t* self) {
+    NVIC_DisableIRQ(self->TC_IRQ);
+    #ifdef SAMD21
+    NVIC_DisableIRQ(EIC_IRQn);
+    #endif
+    #ifdef SAMD51
+    NVIC_DisableIRQ(EIC_0_IRQn + self->channel);
+    #endif
+
+    self->frequency = 0;
+
+    NVIC_ClearPendingIRQ(self->TC_IRQ);
+    NVIC_EnableIRQ(self->TC_IRQ);
+    #ifdef SAMD21
+    NVIC_ClearPendingIRQ(EIC_IRQn);
+    NVIC_EnableIRQ(EIC_IRQn);
+    #endif
+    #ifdef SAMD51
+    NVIC_ClearPendingIRQ(EIC_0_IRQn + self->channel);
+    NVIC_EnableIRQ(EIC_0_IRQn + self->channel);
+    #endif
+    return;
+}
+
+uint16_t common_hal_frequencyio_frequencyin_get_capture_period(frequencyio_frequencyin_obj_t *self) {
+    return self->capture_period;
+}
+
+void common_hal_frequencyio_frequencyin_set_capture_period(frequencyio_frequencyin_obj_t *self, uint16_t capture_period) {
+    if ((capture_period == 0) || (capture_period > 500)) {
+        // TODO: find a sutiable message that is already translated
+        mp_raise_ValueError(translate("Invalid something"));
+    }
+
+    self->capture_period = capture_period;
+
+    common_hal_frequencyio_frequencyin_clear(self);
+}
diff --git a/ports/atmel-samd/common-hal/frequencyio/FrequencyIn.h b/ports/atmel-samd/common-hal/frequencyio/FrequencyIn.h
new file mode 100644
index 0000000000..abd63cc86d
--- /dev/null
+++ b/ports/atmel-samd/common-hal/frequencyio/FrequencyIn.h
@@ -0,0 +1,60 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Michael Schroeder
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef MICROPY_INCLUDED_ATMEL_SAMD_COMMON_HAL_FREQUENCYIO_FREQUENCYIN_H
+#define MICROPY_INCLUDED_ATMEL_SAMD_COMMON_HAL_FREQUENCYIO_FREQUENCYIN_H
+
+#include "common-hal/microcontroller/Pin.h"
+
+#include "py/obj.h"
+
+typedef struct {
+    mp_obj_base_t base;
+    uint8_t tc_index;
+    uint8_t pin;
+    uint8_t channel;
+    uint8_t event_channel;
+    uint32_t frequency;
+    volatile uint64_t last_ms;
+    volatile uint32_t last_us;
+    float factor;
+    uint32_t capture_period;
+    uint8_t TC_IRQ;
+    volatile bool errored_too_fast;
+} frequencyio_frequencyin_obj_t;
+
+void frequencyin_interrupt_handler(uint8_t index);
+void frequencyin_emergency_cancel_capture(uint8_t index);
+void frequencyin_reference_tc_init(void);
+void frequencyin_reference_tc_enable(bool enable);
+bool frequencyin_reference_tc_enabled(void);
+#ifdef SAMD51
+void frequencyin_samd51_start_dpll(void);
+void frequencyin_samd51_stop_dpll(void);
+#endif
+
+
+#endif // MICROPY_INCLUDED_ATMEL_SAMD_COMMON_HAL_FREQUENCYIO_FREQUENCYIN_H
diff --git a/shared-bindings/frequencyio/FrequencyIn.c b/shared-bindings/frequencyio/FrequencyIn.c
new file mode 100644
index 0000000000..0e666d718e
--- /dev/null
+++ b/shared-bindings/frequencyio/FrequencyIn.c
@@ -0,0 +1,238 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Michael Schroeder
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdint.h>
+
+#include "lib/utils/context_manager_helpers.h"
+#include "py/objproperty.h"
+#include "py/runtime.h"
+#include "py/runtime0.h"
+#include "shared-bindings/microcontroller/Pin.h"
+#include "shared-bindings/frequencyio/FrequencyIn.h"
+#include "shared-bindings/util.h"
+#include "supervisor/shared/translate.h"
+
+//| .. currentmodule:: frequencyio
+//|
+//| :class:`FrequencyIn` -- Read a frequency signal
+//| ========================================================
+//|
+//| FrequencyIn is used to measure the frequency, in hertz, of a digital signal
+//| on an incoming pin. Accuracy has shown to be within 1kHz, if not better.
+//| Current maximum detectable frequency is ~512kHz.
+//| It will not determine pulse width (use ``PulseIn``).
+//|
+//| .. class:: FrequencyIn(pin, capture_period=10)
+//|
+//|   Create a FrequencyIn object associated with the given pin.
+//|
+//|   :param ~microcontroller.Pin pin: Pin to read frequency from.
+//|   :param int capture_period: Keyword argument to set the measurement period, in
+//|                              milliseconds. Default is 10ms; maximum is 500ms.
+//|
+//|   Read the incoming frequency from a pin::
+//|
+//|     import frequencyio
+//|     import board
+//|
+//|     frequency = frequencyio.FrequencyIn(board.D11)
+//|
+//|     # Loop while printing the detected frequency
+//|     while True:
+//|         print(frequency.value)
+//|
+//|         # Optional clear() will reset the value
+//|         # to zero. Without this, if the incoming
+//|         # signal stops, the last reading will remain
+//|         # as the value.
+//|         frequency.clear()
+//|
+STATIC mp_obj_t frequencyio_frequencyin_make_new(const mp_obj_type_t *type, size_t n_args,
+         size_t n_kw, const mp_obj_t *pos_args) {
+    mp_arg_check_num(n_args, n_kw, 1, 2, true);
+
+    frequencyio_frequencyin_obj_t *self = m_new_obj(frequencyio_frequencyin_obj_t);
+    self->base.type = &frequencyio_frequencyin_type;
+    mp_map_t kw_args;
+    mp_map_init_fixed_table(&kw_args, n_kw, pos_args + n_args);
+    enum { ARG_pin, ARG_capture_period };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_pin, MP_ARG_REQUIRED | MP_ARG_OBJ },
+        { MP_QSTR_capture_period, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 10} },
+    };
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args, pos_args, &kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    assert_pin(args[ARG_pin].u_obj, false);
+    mcu_pin_obj_t* pin = MP_OBJ_TO_PTR(args[ARG_pin].u_obj);
+    assert_pin_free(pin);
+
+    const uint16_t capture_period = args[ARG_capture_period].u_int;
+
+    common_hal_frequencyio_frequencyin_construct(self, pin, capture_period);
+
+    return MP_OBJ_FROM_PTR(self);
+}
+
+//|   .. method:: deinit()
+//|
+//|      Deinitialises the FrequencyIn and releases any hardware resources for reuse.
+//|
+STATIC mp_obj_t frequencyio_frequencyin_deinit(mp_obj_t self_in) {
+    frequencyio_frequencyin_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    common_hal_frequencyio_frequencyin_deinit(self);
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(frequencyio_frequencyin_deinit_obj, frequencyio_frequencyin_deinit);
+
+//|   .. method:: __enter__()
+//|
+//|      No-op used by Context Managers.
+//|
+//  Provided by context manager helper.
+
+//|   .. method:: __exit__()
+//|
+//|      Automatically deinitializes the hardware when exiting a context. See
+//|      :ref:`lifetime-and-contextmanagers` for more info.
+//|
+STATIC mp_obj_t frequencyio_frequencyin_obj___exit__(size_t n_args, const mp_obj_t *args) {
+    (void)n_args;
+    common_hal_frequencyio_frequencyin_deinit(args[0]);
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(frequencyio_frequencyin___exit___obj, 4, 4, frequencyio_frequencyin_obj___exit__);
+
+//|   .. method:: pause()
+//|
+//|     Pause frequency capture.
+//|
+STATIC mp_obj_t frequencyio_frequencyin_obj_pause(mp_obj_t self_in) {
+    frequencyio_frequencyin_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    raise_error_if_deinited(common_hal_frequencyio_frequencyin_deinited(self));
+
+    common_hal_frequencyio_frequencyin_pause(self);
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(frequencyio_frequencyin_pause_obj, frequencyio_frequencyin_obj_pause);
+
+//|   .. method:: resume()
+//|
+//|     Resumes frequency capture.
+//|
+STATIC mp_obj_t frequencyio_frequencyin_obj_resume(mp_obj_t self_in) {
+    frequencyio_frequencyin_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    raise_error_if_deinited(common_hal_frequencyio_frequencyin_deinited(self));
+
+    common_hal_frequencyio_frequencyin_resume(self);
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(frequencyio_frequencyin_resume_obj, frequencyio_frequencyin_obj_resume);
+
+//|   .. method:: clear()
+//|
+//|     Clears the last detected frequency capture value.
+//|
+
+STATIC mp_obj_t frequencyio_frequencyin_obj_clear(mp_obj_t self_in) {
+    frequencyio_frequencyin_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    raise_error_if_deinited(common_hal_frequencyio_frequencyin_deinited(self));
+
+    common_hal_frequencyio_frequencyin_clear(self);
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(frequencyio_frequencyin_clear_obj, frequencyio_frequencyin_obj_clear);
+
+//|   .. attribute:: capture_period
+//|
+//|     The capture measurement period.
+//|
+//|   .. note:: When setting a new ``capture_period``, all previous capture information is
+//|             cleared with a call to ``clear()``.
+//|
+STATIC mp_obj_t frequencyio_frequencyin_obj_get_capture_period(mp_obj_t self_in) {
+    frequencyio_frequencyin_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    raise_error_if_deinited(common_hal_frequencyio_frequencyin_deinited(self));
+
+    return MP_OBJ_NEW_SMALL_INT(common_hal_frequencyio_frequencyin_get_capture_period(self));
+}
+MP_DEFINE_CONST_FUN_OBJ_1(frequencyio_frequency_get_capture_period_obj, frequencyio_frequencyin_obj_get_capture_period);
+
+STATIC mp_obj_t frequencyio_frequencyin_obj_set_capture_period(mp_obj_t self_in, mp_obj_t capture_period) {
+    frequencyio_frequencyin_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    raise_error_if_deinited(common_hal_frequencyio_frequencyin_deinited(self));
+
+    common_hal_frequencyio_frequencyin_set_capture_period(self, mp_obj_get_int(capture_period));
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_2(frequencyio_frequency_set_capture_period_obj, frequencyio_frequencyin_obj_set_capture_period);
+
+const mp_obj_property_t frequencyio_frequencyin_capture_period_obj = {
+    .base.type = &mp_type_property,
+    .proxy = {(mp_obj_t)&frequencyio_frequency_get_capture_period_obj,
+              (mp_obj_t)&frequencyio_frequency_set_capture_period_obj,
+              (mp_obj_t)&mp_const_none_obj},
+};
+
+//|   .. method:: __get__(index)
+//|
+//|     Returns the value of the last frequency captured.
+//|
+STATIC mp_obj_t frequencyio_frequencyin_obj_get_value(mp_obj_t self_in) {
+    frequencyio_frequencyin_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    raise_error_if_deinited(common_hal_frequencyio_frequencyin_deinited(self));
+
+    //return MP_OBJ_NEW_SMALL_INT(common_hal_frequencyio_frequencyin_get_item(self));
+    return mp_obj_new_int_from_float(common_hal_frequencyio_frequencyin_get_item(self));
+}
+MP_DEFINE_CONST_FUN_OBJ_1(frequencyio_frequencyin_get_value_obj, frequencyio_frequencyin_obj_get_value);
+
+const mp_obj_property_t frequencyio_frequencyin_value_obj = {
+    .base.type = &mp_type_property,
+    .proxy = {(mp_obj_t)&frequencyio_frequencyin_get_value_obj,
+              (mp_obj_t)&mp_const_none_obj,
+              (mp_obj_t)&mp_const_none_obj},
+};
+
+STATIC const mp_rom_map_elem_t frequencyio_frequencyin_locals_dict_table[] = {
+    // Methods
+    { MP_ROM_QSTR(MP_QSTR_deinit), MP_ROM_PTR(&frequencyio_frequencyin_deinit_obj) },
+    { MP_ROM_QSTR(MP_QSTR___enter__), MP_ROM_PTR(&default___enter___obj) },
+    { MP_ROM_QSTR(MP_QSTR___exit__), MP_ROM_PTR(&frequencyio_frequencyin___exit___obj) },
+    { MP_ROM_QSTR(MP_QSTR_value), MP_ROM_PTR(&frequencyio_frequencyin_value_obj) },
+    { MP_ROM_QSTR(MP_QSTR_pause), MP_ROM_PTR(&frequencyio_frequencyin_pause_obj) },
+    { MP_ROM_QSTR(MP_QSTR_resume), MP_ROM_PTR(&frequencyio_frequencyin_resume_obj) },
+    { MP_ROM_QSTR(MP_QSTR_clear), MP_ROM_PTR(&frequencyio_frequencyin_clear_obj) },
+    { MP_ROM_QSTR(MP_QSTR_capture_period), MP_ROM_PTR(&frequencyio_frequencyin_capture_period_obj) },
+};
+STATIC MP_DEFINE_CONST_DICT(frequencyio_frequencyin_locals_dict, frequencyio_frequencyin_locals_dict_table);
+
+const mp_obj_type_t frequencyio_frequencyin_type = {
+    { &mp_type_type },
+    .name = MP_QSTR_frequencyin,
+    .make_new = frequencyio_frequencyin_make_new,
+    .locals_dict = (mp_obj_dict_t*)&frequencyio_frequencyin_locals_dict,
+};
diff --git a/shared-bindings/frequencyio/FrequencyIn.h b/shared-bindings/frequencyio/FrequencyIn.h
new file mode 100644
index 0000000000..4718075ece
--- /dev/null
+++ b/shared-bindings/frequencyio/FrequencyIn.h
@@ -0,0 +1,46 @@
+frequencyio/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Michael Schroeder
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef MICROPY_INCLUDED_SHARED_BINDINGS_FREQUENCYIO_FREQUENCYIN_H
+#define MICROPY_INCLUDED_SHARED_BINDINGS_FREQUENCYIO_FREQUENCYIN_H
+
+#include "common-hal/microcontroller/Pin.h"
+#include "common-hal/frequencyio/FrequencyIn.h"
+
+extern const mp_obj_type_t frequencyio_frequencyin_type;
+
+extern void common_hal_frequencyio_frequencyin_construct(frequencyio_frequencyin_obj_t *self,
+    const mcu_pin_obj_t *pin, uint16_t capture_period);
+extern void common_hal_frequencyio_frequencyin_deinit(frequencyio_frequencyin_obj_t *self);
+extern bool common_hal_frequencyio_frequencyin_deinited(frequencyio_frequencyin_obj_t *self);
+extern void common_hal_frequencyio_frequencyin_pause(frequencyio_frequencyin_obj_t *self);
+extern void common_hal_frequencyio_frequencyin_resume(frequencyio_frequencyin_obj_t *self);
+extern void common_hal_frequencyio_frequencyin_clear(frequencyio_frequencyin_obj_t *self);
+extern uint32_t common_hal_frequencyio_frequencyin_get_item(frequencyio_frequencyin_obj_t *self);
+extern uint16_t common_hal_frequencyio_frequencyin_get_capture_period(frequencyio_frequencyin_obj_t *self);
+extern void common_hal_frequencyio_frequencyin_set_capture_period(frequencyio_frequencyin_obj_t *self, uint16_t capture_period);
+
+#endif // MICROPY_INCLUDED_SHARED_BINDINGS_FREQUENCYIO_FREQUENCYIN_H
diff --git a/shared-bindings/frequencyio/__init__.c b/shared-bindings/frequencyio/__init__.c
new file mode 100644
index 0000000000..8e794eac4a
--- /dev/null
+++ b/shared-bindings/frequencyio/__init__.c
@@ -0,0 +1,88 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Scott Shawcroft for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdint.h>
+
+#include "py/obj.h"
+#include "py/runtime.h"
+
+#include "shared-bindings/microcontroller/Pin.h"
+#include "shared-bindings/frequencyio/FrequencyIn.h"
+
+//| :mod:`frequencyio` --- Support for frequency based protocols
+//| =============================================================
+//|
+//| .. module:: frequencyio
+//|   :synopsis: Support for frequency based protocols
+//|   :platform: SAMD51
+//|
+//| The `frequencyio` module contains classes to provide access to basic frequency IO.
+//|
+//| Libraries
+//|
+//| .. toctree::
+//|     :maxdepth: 3
+//|
+//|     FrequencyIn
+//|
+
+//| .. warning:: This module is not available in SAMD21 builds. See the
+//|   :ref:`module-support-matrix` for more info.
+//|
+
+//| All classes change hardware state and should be deinitialized when they
+//| are no longer needed if the program continues after use. To do so, either
+//| call :py:meth:`!deinit` or use a context manager. See
+//| :ref:`lifetime-and-contextmanagers` for more info.
+//|
+//| For example::
+//|
+//|   import frequencyio
+//|   import time
+//|   from board import *
+//|
+//|   frequency = frequencyio.FrequencyIn(D13)
+//|   frequency.capture_period = 15
+//|   time.sleep(0.1)
+//|
+//| This example will initialize the the device, set
+//| :py:data:`~frequencyio.FrequencyIn.capture_period`, and then sleep 0.1 seconds.
+//| CircuitPython will automatically turn off FrequencyIn capture when it resets all
+//| hardware after program completion. Use ``deinit()`` or a ``with`` statement
+//| to do it yourself.
+//|
+
+STATIC const mp_rom_map_elem_t frequencyio_module_globals_table[] = {
+    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_frequencyio) },
+    { MP_ROM_QSTR(MP_QSTR_FrequencyIn), MP_ROM_PTR(&pulseio_frequencyin_type) },
+};
+
+STATIC MP_DEFINE_CONST_DICT(frequencyio_module_globals, frequencyio_module_globals_table);
+
+const mp_obj_module_t frequencyio_module = {
+    .base = { &mp_type_module },
+    .globals = (mp_obj_dict_t*)&frequencyio_module_globals,
+};