esp-idf-mirf

A port of the Mirf library for ESP-IDF.
The library provides basic control of the Nordic nRF24L01/nRF24L01+ RF modules.

I ported from here.

Software requirements

ESP-IDF V4.4/V5.x.
ESP-IDF V5.0 is required when using ESP32-C2.
ESP-IDF V5.1 is required when using ESP32-C6.

Installation

git clone https://github.com/nopnop2002/esp-idf-mirf
cd esp-idf-mirf/Peer-to-peer
idf.py set-target {esp32/esp32s2/esp32s3/esp32c2/esp32c3/esp32c6}
idf.py menuconfig
idf.py flash

Note for ESP32C3
For some reason, there are development boards that cannot use GPIO06, GPIO08, GPIO09, GPIO19 for SPI clock pins.
According to the ESP32C3 specifications, these pins can also be used as SPI clocks.
I used a raw ESP-C3-13 to verify that these pins could be used as SPI clocks.

Configuration for Transceiver

Note for Channel
Channels range from 0 to 127.
The channel number of the sender and receiver must be the same.
Channel = 0 uses the frequency of 2.4000GHz, channel = 127 uses the frequency of 2.4127GHz.
The width of one channel is only 0.01GHz.
Using multiple radio node at the same time will almost always cause interference, even if you change channels.

SPI BUS selection

The ESP32 series has three SPI BUSs.
SPI1_HOST is used for communication with Flash memory.
You can use SPI2_HOST and SPI3_HOST freely.
When you use SDSPI(SD Card via SPI), SDSPI uses SPI2_HOST BUS.
When using this module at the same time as SDSPI or other SPI device using SPI2_HOST, it needs to be changed to SPI3_HOST.
When you don't use SDSPI, both SPI2_HOST and SPI3_HOST will work.
Previously it was called HSPI_HOST / VSPI_HOST, but now it is called SPI2_HOST / SPI3_HOST.

SPI Clock speed

According to the nRF24L01 datasheet, maximum data rate of 8MHz.
The SPI clock frequency used by this project is 4MHz.
Changing it to 8MHz has almost no effect.

Using Advanced Settings

When used at long distances, lowering the RF data rate stabilizes it.
When changing the RF data rate, the sender and receiver must have the same value.
When using 250KBps, it takes time to PAYLOAD sending and ACK PACKET receiving, so it is necessary to increase the automatic retransmission delay.
I tested it with this.

If you want to initialize the nRF24L01 settings after using the Advanced Settings, you need to power cycle the nRF24L01 before executing.
Because nRF24L01 remembers the previous setting.
nRF24L01 does not have Software Reset function.

Wirering

nRF24L01		ESP32	ESP32-S2/S3	ESP32-C2/C3/C6
MISO	--	GPIO19	GPIO37	GPIO4	(*1)
SCK	--	GPIO18	GPIO36	GPIO3	(*1)
MOSI	--	GPIO23	GPIO35	GPIO2	(*1)
CE	--	GPIO16	GPIO34	GPIO1	(*1)
CSN	--	GPIO17	GPIO33	GPIO0	(*1)
GND	--	GND	GND	GND
VCC	--	3.3V	3.3V	3.3V

(*1)You can change it to any pin using menuconfig.

Communicat with Arduino Environment

I used this library on Arduino environment.
You need to match the payload size and channel with Arduino and esp-idf.

• Arduino environment

Mirf.payload = sizeof(mydata.value);
Mirf.channel = 90;
Mirf.config();

• esp-idf

uint8_t payload = sizeof(value);
uint8_t channel = 90;
Nrf24_config(&dev, channel, payload);

Communicat with Raspberry Pi

I used this library on Raspberry Pi.

Using binary data

nRF24L01 is not interested in the contents of the payload.
Therefore, nRF24L01 can send and receive binary data.
But the internal format of the binary data depends on the MCU architecture, so communication between different architectures is not possible.
If you want to send or receive binary data between different architectures, you need to encode it into a CSV format string like this.
123,-123,1234.5,-1234.5
nRF24L01 can send and receive up to 32 characters, but by adding an index to the sent data, it can send and receive 256 types of data.

Important

When changing the settings of the nRF24L01, it is necessary to power cycle the nRF24L01 before executing.
Because nRF24L01 remembers the previous setting.
nRF24L01 does not have Software Reset function.

Enhanced ShockBurst overview

The following is reprinted from nRF24L01 Single Chip 2.4GHz Transceiver Product Specification.
Enhanced ShockBurst is a trademark of NORDIC.

Enhanced ShockBurst features automatic packet transaction handling that enables the implementation of a reliable bi-directional data link.
An Enhanced ShockBurst packet transaction is a packet exchange between to transceivers, where one transceiver is the Primary Receiver (PRX) and the other is the Primary Transmitter (PTX).
An Enhanced ShockBurst packet transaction is always initiated by a packet transmission from the PTX, the transaction is complete when the PTX has received an acknowledgment packet (ACK packet) from the PRX.
The automatic packet transaction handling works as follows:

• The user initiates the transaction by transmitting a data packet from the PTX to the PRX. Enhanced ShockBurst automatically sets the PTX in receive mode to wait for the ack packet.
• If the packet is received by the PRX, Enhanced ShockBurst automatically assembles and transmits an acknowledgment packet (ACK packet) to the PTX before returning to receive mode.
• If the PTX does not receive the ACK packet within a set time, Enhanced ShockBurst will automatically retransmit the original data packet and set the PTX in receive mode to wait for the ACK packet.

The PRX can attach user data to the ACK packet enabling a bi-directional data link.
The Enhanced Shock-Burst is highly configurable; it is possible to configure parameters such as maximum number of retransmits and the delay from one transmission to the next retransmission.
All automatic handling is done without involvement of the MCU.

Transmission Successful

ESP32		nRF24L01[PTX]		nRF24L01[PRX]		ESP32
ESP32	-->	nRF24L01
		nRF24L01	--(Payload Packet)-->	nRF24L01
			wait 250uS
		nRF24L01	<--(Ack Packet)--	nRF24L01
ESP32	<--	nRF24L01
				nRF24L01	-->	ESP32

Transmission Failure

PTX waits for an ACK packet for 250uS and retransmits 3 times.

ESP32		nRF24L01[PTX]		nRF24L01[PRX]		ESP32
ESP32	-->	nRF24L01
		nRF24L01	--(Payload Packet)-->	nRF24L01
			wait 250uS
		nRF24L01	--(Payload Packet)-->	nRF24L01
			wait 250uS
		nRF24L01	--(Payload Packet)-->	nRF24L01
			wait 250uS
ESP32	<--	nRF24L01

Using a data rate of 250KBps extends the range of radio waves.
However, it takes time to send PAYLOAD and receive ACK PACKET.
Therefore, the delay time for automatic retransmission should be longer than 250uS.
If the delay of automatic retransmission is not increased, it is considered as a transmission failure.

ESP32		nRF24L01[PTX]		nRF24L01[PRX]		ESP32
ESP32	-->	nRF24L01
		nRF24L01	--(Payload Packet)-->	nRF24L01
			Over 250uS
		nRF24L01	<--(Ack Packet)--	nRF24L01
ESP32	<--	nRF24L01
				nRF24L01	-->	ESP32

See the data sheet for details on Enhanced ShockBurst.

Throughput

spi_device_transmit is executed by the SPI driver and consumes 1tick of CPU time.
When DMA is enabled, SPI max_transfer_sz defaults to 4092(4K).
This indicates that 4092 bytes of data can be sent in 1tick(10 millsec).
Therefore, the SPI transmission potential of ESP-IDF is 400Kbytes/Sec.
This has a significant impact on the nRF24L01, which has a small maximum payload size.

Unfortunately, nRF24L01's maximum payload size is 32 bytes.
1 tick (10 millsec) is required to send payload and receive ack packet.
This has nothing to do with SPI bus speed.
The throughput of nRF24L01 is 32 bytes/10 millsec(=3,200 bytes/sec).
RF data rate of nRF24L01 affects the radio range, but not the throughput.

About Si24R1 clone

Si24R1 is marketed as a nRF24L01 compatible.
Si24R1 clone cannot send and receive correctly.
After purchasing the nRF24L01, be sure to check the markings on the chip.
Many suppliers sell Si24R1 as nRF24L01.