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diff --git a/circuitpython/lib/protomatter/src/arch/nrf52.h b/circuitpython/lib/protomatter/src/arch/nrf52.h
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+/*!
+ * @file nrf52.h
+ *
+ * Part of Adafruit's Protomatter library for HUB75-style RGB LED matrices.
+ * This file contains NRF52-SPECIFIC CODE.
+ *
+ * Adafruit invests time and resources providing this open source code,
+ * please support Adafruit and open-source hardware by purchasing
+ * products from Adafruit!
+ *
+ * Written by Phil "Paint Your Dragon" Burgess and Jeff Epler for
+ * Adafruit Industries, with contributions from the open source community.
+ *
+ * BSD license, all text here must be included in any redistribution.
+ *
+ */
+
+#pragma once
+
+#if defined(NRF52_SERIES)
+
+#if defined(ARDUINO) // COMPILING FOR ARDUINO ------------------------------
+
+// digitalPinToPort, g_ADigitalPinMap[] are Arduino specific:
+
+void *_PM_portOutRegister(uint32_t pin) {
+  NRF_GPIO_Type *port = digitalPinToPort(pin);
+  return &port->OUT;
+}
+
+void *_PM_portSetRegister(uint32_t pin) {
+  NRF_GPIO_Type *port = digitalPinToPort(pin);
+  return &port->OUTSET;
+}
+
+void *_PM_portClearRegister(uint32_t pin) {
+  NRF_GPIO_Type *port = digitalPinToPort(pin);
+  return &port->OUTCLR;
+}
+
+// Leave _PM_portToggleRegister(pin) undefined on nRF!
+
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define _PM_byteOffset(pin) ((g_ADigitalPinMap[pin] & 0x1F) / 8)
+#define _PM_wordOffset(pin) ((g_ADigitalPinMap[pin] & 0x1F) / 16)
+#else
+#define _PM_byteOffset(pin) (3 - ((g_ADigitalPinMap[pin] & 0x1F) / 8))
+#define _PM_wordOffset(pin) (1 - ((g_ADigitalPinMap[pin] & 0x1F) / 16))
+#endif
+
+// Because it's tied to a specific timer right now, there can be only
+// one instance of the Protomatter_core struct. The Arduino library
+// sets up this pointer when calling begin().
+void *_PM_protoPtr = NULL;
+
+// Arduino implementation is tied to a specific timer/counter,
+// Partly because IRQs must be declared at compile-time.
+#define _PM_IRQ_HANDLER TIMER4_IRQHandler
+#define _PM_timerFreq 16000000
+#define _PM_TIMER_DEFAULT NRF_TIMER4
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Timer interrupt service routine
+void _PM_IRQ_HANDLER(void) {
+  if (_PM_TIMER_DEFAULT->EVENTS_COMPARE[0]) {
+    _PM_TIMER_DEFAULT->EVENTS_COMPARE[0] = 0;
+  }
+  _PM_row_handler(_PM_protoPtr); // In core.c
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#elif defined(CIRCUITPY) // COMPILING FOR CIRCUITPYTHON --------------------
+
+#include "nrf_gpio.h"
+
+volatile uint32_t *_PM_portOutRegister(uint32_t pin) {
+  NRF_GPIO_Type *port = nrf_gpio_pin_port_decode(&pin);
+  return &port->OUT;
+}
+
+volatile uint32_t *_PM_portSetRegister(uint32_t pin) {
+  NRF_GPIO_Type *port = nrf_gpio_pin_port_decode(&pin);
+  return &port->OUTSET;
+}
+
+volatile uint32_t *_PM_portClearRegister(uint32_t pin) {
+  NRF_GPIO_Type *port = nrf_gpio_pin_port_decode(&pin);
+  return &port->OUTCLR;
+}
+#define _PM_pinOutput(pin)                                                     \
+  nrf_gpio_cfg(pin, NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_DISCONNECT,    \
+               NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE)
+#define _PM_pinInput(pin) nrf_gpio_cfg_input(pin)
+#define _PM_pinHigh(pin) nrf_gpio_pin_set(pin)
+#define _PM_pinLow(pin) nrf_gpio_pin_clear(pin)
+#define _PM_portBitMask(pin) (1u << ((pin)&31))
+
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define _PM_byteOffset(pin) ((pin & 31) / 8)
+#define _PM_wordOffset(pin) ((pin & 31) / 16)
+#else
+#define _PM_byteOffset(pin) (3 - ((pin & 31) / 8))
+#define _PM_wordOffset(pin) (1 - ((pin & 31) / 16))
+#endif
+
+// CircuitPython implementation is tied to a specific freq (but the counter
+// is dynamically allocated):
+#define _PM_timerFreq 16000000
+
+// Because it's tied to a specific timer right now, there can be only
+// one instance of the Protomatter_core struct. The Arduino library
+// sets up this pointer when calling begin().
+void *_PM_protoPtr = NULL;
+
+// Timer interrupt service routine
+void _PM_IRQ_HANDLER(void) {
+  NRF_TIMER_Type *timer = (((Protomatter_core *)_PM_protoPtr)->timer);
+  if (timer->EVENTS_COMPARE[0]) {
+    timer->EVENTS_COMPARE[0] = 0;
+  }
+
+  _PM_row_handler(_PM_protoPtr); // In core.c
+}
+
+#else // END CIRCUITPYTHON -------------------------------------------------
+
+// Byte offset macros, timer and ISR work for other environments go here.
+
+#endif
+
+// CODE COMMON TO ALL ENVIRONMENTS -----------------------------------------
+
+void _PM_timerInit(void *tptr) {
+  static const struct {
+    NRF_TIMER_Type *tc; // -> Timer peripheral base address
+    IRQn_Type IRQn;     // Interrupt number
+  } timer[] = {
+#if defined(NRF_TIMER0)
+    {NRF_TIMER0, TIMER0_IRQn},
+#endif
+#if defined(NRF_TIMER1)
+    {NRF_TIMER1, TIMER1_IRQn},
+#endif
+#if defined(NRF_TIMER2)
+    {NRF_TIMER2, TIMER2_IRQn},
+#endif
+#if defined(NRF_TIMER3)
+    {NRF_TIMER3, TIMER3_IRQn},
+#endif
+#if defined(NRF_TIMER4)
+    {NRF_TIMER4, TIMER4_IRQn},
+#endif
+  };
+#define NUM_TIMERS (sizeof timer / sizeof timer[0])
+
+  // Determine IRQn from timer address
+  uint8_t timerNum = 0;
+  while ((timerNum < NUM_TIMERS) && (timer[timerNum].tc != tptr)) {
+    timerNum++;
+  }
+  if (timerNum >= NUM_TIMERS)
+    return;
+
+  NRF_TIMER_Type *tc = timer[timerNum].tc;
+
+  tc->TASKS_STOP = 1;               // Stop timer
+  tc->MODE = TIMER_MODE_MODE_Timer; // Timer (not counter) mode
+  tc->TASKS_CLEAR = 1;
+  tc->BITMODE = TIMER_BITMODE_BITMODE_16Bit
+                << TIMER_BITMODE_BITMODE_Pos; // 16-bit timer res
+  tc->PRESCALER = 0;                          // 1:1 prescale (16 MHz)
+  tc->INTENSET = TIMER_INTENSET_COMPARE0_Enabled
+                 << TIMER_INTENSET_COMPARE0_Pos; // Event 0 interrupt
+  // NVIC_DisableIRQ(timer[timerNum].IRQn);
+  // NVIC_ClearPendingIRQ(timer[timerNum].IRQn);
+  // NVIC_SetPriority(timer[timerNum].IRQn, 0); // Top priority
+  NVIC_EnableIRQ(timer[timerNum].IRQn);
+}
+
+inline void _PM_timerStart(void *tptr, uint32_t period) {
+  volatile NRF_TIMER_Type *tc = (volatile NRF_TIMER_Type *)tptr;
+  tc->TASKS_STOP = 1;  // Stop timer
+  tc->TASKS_CLEAR = 1; // Reset to 0
+  tc->CC[0] = period;
+  tc->TASKS_START = 1; // Start timer
+}
+
+inline uint32_t _PM_timerGetCount(void *tptr) {
+  volatile NRF_TIMER_Type *tc = (volatile NRF_TIMER_Type *)tptr;
+  tc->TASKS_CAPTURE[0] = 1; // Capture timer to CC[n] register
+  return tc->CC[0];
+}
+
+uint32_t _PM_timerStop(void *tptr) {
+  volatile NRF_TIMER_Type *tc = (volatile NRF_TIMER_Type *)tptr;
+  tc->TASKS_STOP = 1; // Stop timer
+  __attribute__((unused)) uint32_t count = _PM_timerGetCount(tptr);
+  // NOTE TO FUTURE SELF: I don't know why the GetCount code isn't
+  // working. It does the expected thing in a small test program but
+  // not here. I need to get on with testing on an actual matrix, so
+  // this is just a nonsense fudge value for now:
+  return 100;
+  // return count;
+}
+
+#define _PM_clockHoldHigh asm("nop; nop");
+
+#define _PM_minMinPeriod 100
+
+#endif // END NRF52_SERIES