Use the IRQ signal from the nrf24l01 instead of polling the status

This is done to avoid transmission erros as described in
https://forum.mysensors.org/topic/10452/nrf24l01-communication-failure-root-cause-and-solution

weather-sensor/firmware/led.h

+#ifndef LED_H
+#define LED_H
+
+#define LED_DDR   DDRD
+#define LED_PORT  PORTD
+#define LED_PIN   PD3
+
+#endif

weather-sensor/firmware/main.c

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdbool.h>
 
+#include "led.h"
 #include "spi.h"
 #include "nrf24l01.h"
 #include "nrf24l01_definitions.h"
 
 
 
-/* Debug LED: */
-#define LED_DDR   DDRD
-#define LED_PORT  PORTD
-#define LED_PIN   PD3
 
 
 char bool_case = 0;
 
 volatile uint8_t cycle = 0;
 
+volatile bool nrfInterruptRaised;
+
 volatile uint8_t interruptCounter;
 volatile uint8_t executionFlag;
 
 void Enter_Power_Save_Mode(void);
 
 
-ISR( TIMER2_COMPA_vect )
+ISR(TIMER2_COMPA_vect)
 {
 	/* Do nothing as the interrupt is only used to wake up the MCU. */
 }
 
+ISR(PCINT2_vect)
+{
+	nrfInterruptRaised = true;
+}
+
 int main (void)
 {
 	struct bme280_data sensorData;
 //	uint8_t registerContent[5];
 //	char registerContentString[30];
 //	uint8_t lengthRead;
-	uint8_t temp = 0;
 
 	/* Enable the debug LED */
 	LED_DDR |= (1 << LED_PIN);
 			BME280_Get_Measurement(&sensorData);
 			NRF24L01_Send_Message((uint8_t*)&sensorData, sizeof(sensorData));
 
-			if (temp == 0)
-			{
-				LED_PORT |= (1 << LED_PIN);
-				temp = 1;
-			}
-			else
-			{
-				temp = 0;
-				LED_PORT &= ~(1 << LED_PIN);
-			}
+			_delay_ms(100); /* TODO: only for debugging, remove this later! */
+			LED_PORT &= ~(1 << LED_PIN);
 
 			cycle = 0;
 		}

weather-sensor/firmware/makefile

 	rm -f main
 
 flash: main.hex
-	sudo avrdude -c buspirate -b 115200 -P /dev/ttyUSB0 -p m88p -v -U flash:w:main.hex
+	sudo avrdude -c buspirate -b 115200 -P /dev/ttyUSB1 -p m88p -v -U flash:w:main.hex
 
-main: main.c spi.c spi.h nrf24l01.c nrf24l01.h nrf24l01_definitions.h bme280_interface.c bme280_interface.h BME280_driver/bme280.c BME280_driver/bme280.h
+main: main.c spi.c spi.h nrf24l01.c nrf24l01.h nrf24l01_definitions.h bme280_interface.c bme280_interface.h BME280_driver/bme280.c BME280_driver/bme280.h led.h
 	avr-gcc main.c spi.c nrf24l01.c bme280_interface.c BME280_driver/bme280.c -I BME280_driver -o main -mmcu=atmega88p -Os -Wall -Wextra -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -DF_CPU=1000000UL -D BME280_32BIT_ENABLE
 
 main.hex: main

weather-sensor/firmware/nrf24l01.c

 #include <stdio.h>
 #include <stdbool.h>
 
+#include "led.h" // TODO: for debugging
 #include "spi.h"
 #include "nrf24l01.h"
 #include "nrf24l01_definitions.h"
 
 /* TODO
- * - Build a state machine that tracks the mode the NRF is set to
- * - Configuration of NRF24L01 and startup
- * - Send and Receive functions
- * - Interrupt handling for Send and Receive
+ * - Send functions
+ * - Interrupt handling for Send
  */
 
+extern volatile bool nrfInterruptRaised;
+
 void Print_Register_Contents(uint8_t address);
 void Send_TX_Flush_Command(void);
 
 
 	/* Ensure that the CE pin is set to 0*/
 	NRF_CE_PORT &= ~(1 << NRF_CE_PIN);
+
+	/* Set the interrupt pin */
+	/* TODO: PCINT21 -> PCINT2 */
+	NRF_IRQ_DDR &= ~(1 << NRF_IRQ_PIN); // Set the pin as input
+	NRF_IRQ_PORT |= (1 << NRF_IRQ_PORT); // Enable the pullup for the pin
 }
 
 void Configure_Transmission(void)
 	Set_TX_Address(0x123456);
 
 	Set_RX_P0_Address(0x123456);
-	
-
 	// TODO: set addresses for all data pipes
+
+
+	PCMSK2 |= (1<<PCINT21); // Set the external interrupt for PD5
 }
 
 void NRF24L01_Send_Message(uint8_t *buffer, uint8_t length)
 {
-	bool transmissionFinished = false;
-
 	STATUS_REGISTER statusRegisterContents = {.byte = 0x0};
-	uint32_t timeout = 0;
-	/* TODO:
-	 * - if needed: PRIM_RX = 0
-	 * - Set CE = 1 for more than 10 us
-	 * - Wait until the transmission is finished
-	 * - Read number of retries for debug purposes
-	 * - Check if the FIFO is empty -> if not, flush it
-	 * - reset the interupts of the STATUS
-	 */
 	
-	/* TODO: messages with more than 32 byte length */
 	if ((length > 32) || (length == 0))
 	{
 		return;
 	}
 
+	PCICR |= (1<<PCIE2); // Enable the interrupt for the IRQ signal
+
 	Write_Message_To_TX_FIFO(length, buffer);
 
 	/* Set CE = 1 for more than 10 us */
 	_delay_us(15);
 	NRF_CE_PORT &= ~(1 << NRF_CE_PIN);
 
+	while (nrfInterruptRaised == false); // Wait until the transmission is complete
+	/* An interrupt instead of polling the status register is used to avoid transmission errors
+	 * induced by the SPI:
+	 * https://forum.mysensors.org/topic/10452/nrf24l01-communication-failure-root-cause-and-solution
+	 */
+	LED_PORT |= (1 << LED_PIN);
 
-	do
+	statusRegisterContents.byte = Read_NRF_Status_Register();
+
+
+	if (statusRegisterContents.bits.MAX_RT == 1)
 	{
-		_delay_ms(1);
-		/* TODO: instead of polling the status register use the IRQ to spawn an interrupt as the
-		 * constant polling may induce transmission errors:
-		 * https://forum.mysensors.org/topic/10452/nrf24l01-communication-failure-root-cause-and-solution
-		 */
-		statusRegisterContents.byte = Read_NRF_Status_Register();
-
-		if (statusRegisterContents.bits.TX_DS == 1)
-		{
-			transmissionFinished = true;
-		}
-
-		if (statusRegisterContents.bits.MAX_RT == 1)
-		{
-			transmissionFinished = true; //TODO: indicate failure
-
-			Send_TX_Flush_Command(); /* Remove the packet from the TX FIFO as it is not done automatically */
-		}
-		
-		timeout ++; // TODO: this should work without the time out, as MAX_RT should be triggered if no ACK is received
-	} while ((transmissionFinished == false) && (timeout < 0xFF));
+		Send_TX_Flush_Command(); /* Remove the packet from the TX FIFO as it is not done automatically */
+	}
+	
 
 	/* Reset the interrupts */
-	statusRegisterContents.byte = Read_NRF_Status_Register();
 	statusRegisterContents.bits.TX_DS = 1;
 	statusRegisterContents.bits.MAX_RT = 1;
+	statusRegisterContents.bits.RX_DR = 1;
 	Write_NRF_Register(STATUS_ADDRESS, statusRegisterContents.byte);
+
+	PCICR &= ~(1<<PCIE2); // Disable the interrupt for the IRQ signal
+	nrfInterruptRaised = false;
+
+
+	return;
 }
 
 void Print_Register_Contents(uint8_t address)

weather-sensor/firmware/nrf24l01.h

 #define NRF_CSN_PORT  PORTD
 #define NRF_CSN_PIN   PD6
 
-#define NRF_IRQ_DDR   DDRD
-#define NRF_IRQ_PORT  PORTD
-#define NRF_IRQ_PIN   PD5
+#define NRF_IRQ_DDR     DDRD
+#define NRF_IRQ_PORT    PORTD
+#define NRF_IRQ_PIN     PD5
+#define NRF_IRQ_PORTIN  PIND
 
 void Initialize_NRF24L01(void);
 void Set_NRF24L01_Pins(void);