The initial objective of this blog is to understand how to use and configure both the Zephyr I2C/TWI Master and Slave drivers. However, no Zephyr I2C/TWIS Slave Driver supports Nordic I2C/TWI Slave hardware to date. As a result, the TWIM software will use the Zephyr i2c driver, and the TWIS software will use the nRFX driver (NRFX_DRV) paradigm. So, this tutorial also provides insight into integrating a Nordic nRFX driver into NRF Connect SDK.
It is assumed the reader has already installed nRF Connect SDK, the required Toolchain, and is familiar with the process of adding a peripheral to an application. If the reader is unfamiliar with this process, it is recommended to first review Adding a Peripheral to an NCS Zephyr project. The sample code for the Master and Slave will use TWIM1 and TWIS0, respectively. Using the technique provided in Adding a Peripheral to an NCS Zephyr project to merge the Master and Slave examples, one could implement the functionality of this tutorial on a single DK.
The tutorial portion of this document is based on NRF Connect SDK version 1.6.1 and requires the use of two nRF52840-DKs.
The tutorial will demonstrate how to add support for a TWI Master (TWIM) and TWI Slave (TWIS). The initial application for both TWIM and TWIS applications is <install directory> \zephyr\samples\basic\blinky.
The provided code is configured to write a fixed message “MSG FROM TWIM” to the TWIS. But by setting TWI_LOOPBACK to true the TWIM will first write the message “Begin Loopback.” Each subsequent message written by the TWIM will echo the previously received message fragment read from the TWIS. The complete TWIS message is “This is a circular TWIS transmit buffer.”
If any information in this document contradicts the referenced documentation, the reference documentation is assumed to be more accurate.
Though technically different constructs, TWI and I2C are often considered to be operationally synonymous. Nordic has adopted the TWI nomenclature, while Zephyr has adopted I2C. For this document, I2C will only be used to be consistent with referenced Zephyr software and documentation.
/* Overlay for TWI/IC2 Zephyr NCS implementation with nRFx TWIM Driver */
/* Line references are used in the blog post and twim_node.txt */
&i2c1 { /* a */
compatible = "nordic,nrf-twim"; /* b */
status = "okay"; /* c */
clock-frequency = <100000>; /* d */
twis_device1:nRF52840@28 { /* e */
// device compatible /* f */
label = "i2c nRF52840 addr 0x28"; /* g */
reg = <0x28>; /* h */
};
}; CONFIG_I2C=y CONFIG_I2C_NRFX=y
/*
* Copyright (c) 2016 Intel Corporation
*
* SPDX-License-Identifier: Apache-2.0
*/
#include <device.h>
#include <devicetree.h>
#include <drivers/gpio.h>
#include <drivers/i2c.h>
#include <sys/printk.h>
#include <zephyr.h>
/* 1000 msec = 1 sec */
#define SLEEP_TIME_MS 1000
/* The devicetree node identifier for the "led0" alias. */
#define LED0_NODE DT_ALIAS(led0)
const struct device *led_dev;
#if DT_NODE_HAS_STATUS(LED0_NODE, okay)
#define LED0 DT_GPIO_LABEL(LED0_NODE, gpios)
#define PIN DT_GPIO_PIN(LED0_NODE, gpios)
#define FLAGS DT_GPIO_FLAGS(LED0_NODE, gpios)
#else
/* A build error here means your board isn't set up to blink an LED. */
#error "Unsupported board: led0 devicetree alias is not defined"
#define LED0 ""
#define PIN 0
#define FLAGS 0
#endif
////////////////////////////////////////////////////////////
// TWI Test Configuration
////////////////////////////////////////////////////////////
#define ECHO_WRITES false
#define MSG_EXCHANGE_CNT 5
#define INFINITE_MSG_EXCHANGE false
#define TWI_LOOPBACK false
// In non-loopback mode, the tx message is unchanged.
// In loopback mode the rx buffer acts as both the tx and rx buffer. The rx buffer is updated with each read.
////////////////////////////////////////////////////////////
// Adding TWI Functionality
////////////////////////////////////////////////////////////
#define TWI_BUFFER_SIZE 14
static unsigned char i2c_tx_buffer[TWI_BUFFER_SIZE] = {'M', 'S','G',' ','F', 'R', 'O', 'M', ' ', 'T', 'W', 'I', 'M', '\0'};
static unsigned char i2c_rx_buffer[TWI_BUFFER_SIZE] = "Begin Loopback";
// TWI Master Setup
#define MY_TWIM DT_NODELABEL(i2c1)
const struct device *nrfx_twis_dev1;
static void twim_init(void) {
int config_result = false;
nrfx_twis_dev1 = device_get_binding(DT_LABEL(MY_TWIM));
if (nrfx_twis_dev1 == NULL) {
printk("\n\nI2C Slave: Device driver not found.\n");
} else {
printk("\nI2C device 1: %s\n", DT_PROP(DT_NODELABEL(twis_device1), label));
config_result = i2c_configure(nrfx_twis_dev1, I2C_SPEED_SET(I2C_SPEED_FAST) | I2C_MODE_MASTER);
if (!config_result) {
printk("I2C Master: Slave ADDR: 0x%x SCL: %d, SDA: %d, CLK(Hz): %u\n\n",
DT_REG_ADDR(DT_NODELABEL(twis_device1)),
DT_PROP(MY_TWIM, scl_pin),
DT_PROP(MY_TWIM, sda_pin),
DT_PROP(MY_TWIM, clock_frequency));
} else
printk("\n\nI2C: Configuration error code: %d\n", config_result);
}
}
// TWI Master Write
void twi_write_tst(void){
int rtn_code = 0;
uint8_t incr = 0;
bool loopback = TWI_LOOPBACK;
if (nrfx_twis_dev1 != NULL) {
// printk("\nTWIM TX/writing.");
if (!loopback) { //write repeated default message
rtn_code = i2c_write(nrfx_twis_dev1, i2c_tx_buffer, sizeof(i2c_tx_buffer), DT_REG_ADDR(DT_NODELABEL(twis_device1)));
}else{ //use read buffer as write buffer
rtn_code = i2c_write(nrfx_twis_dev1, i2c_rx_buffer, sizeof(i2c_rx_buffer), DT_REG_ADDR(DT_NODELABEL(twis_device1)));
}
if (ECHO_WRITES && (rtn_code == 0)){
printk("\nTWIM TX:");
while (incr < TWI_BUFFER_SIZE)
printk("%c", i2c_rx_buffer[incr++]);
printk("\n");
} //rtn_code == 0
if (rtn_code){
printk("twi return code %u\n\n", rtn_code);
}
} else // twis_dev1 == NULL
printk("TWIS device is not initialized correctly.\n");
}
void twi_read_tst(void){
int rtn_code = 0;
uint8_t incr = 0;
if (nrfx_twis_dev1 != NULL) {
// printk("\nTWIM RX/reading -->");
rtn_code = i2c_read(nrfx_twis_dev1, i2c_rx_buffer, sizeof(i2c_rx_buffer), DT_REG_ADDR(DT_NODELABEL(twis_device1)));
if (rtn_code == 0) {
printk("TWIM RX:");
while (incr < TWI_BUFFER_SIZE) {
printk("%c", i2c_rx_buffer[incr++]);
};
printk("\n");
}
if (rtn_code)
printk("twi return code %u\n\n", rtn_code);
} else //twim_dev1 == NULL
printk("TWI is not initialized correctly.\n");
}
void main(void) {
uint16_t twi_test_cnt = MSG_EXCHANGE_CNT;
bool led_is_on = true;
uint32_t ret;
led_dev = device_get_binding(LED0);
if (led_dev == NULL) {
return;
}
ret = gpio_pin_configure(led_dev, PIN, GPIO_OUTPUT_ACTIVE | FLAGS);
if (ret < 0) {
return;
}
twim_init();
while(1){
gpio_pin_set(led_dev, PIN, (int)led_is_on);
led_is_on = !led_is_on;
if((twi_test_cnt) || (INFINITE_MSG_EXCHANGE)){
twi_write_tst();
twi_read_tst();
if(twi_test_cnt){
twi_test_cnt--;
}
if((!twi_test_cnt) && (!INFINITE_MSG_EXCHANGE)){
printk("\n\nTo rerun this test, reset the master.\n\n");
}
}
k_msleep(SLEEP_TIME_MS);
}
}/* Overlay for TWI/IC2 Zephyr NCS implementation with nRFx TWIS Driver */
/* Line references are used in the blog post and twis_node.txt */
&i2c0 { /* a */
/* b */
status = "disabled"; /* c */
sda-pin = <26>; /* d */
scl-pin = <27>; /* e */
interrupts = < 0x4 0x2 >; /* f */
twis_device1:nRF52804@28 { /* g */
label = "i2c nRF52840 addr 0x28"; /* h */
reg = <0x28>; /* i */
};
twis_device2: nRF52840@0 { /* j */
label = "i2c nRF52840 addr 0x00"; /* k */
reg = <0x0>; /* l */
};
};
&spi0 { /* m */
status = "disabled"; /* n */
};CONFIG_NRFX_TWIS1=y
/*
* Copyright (c) 2016 Intel Corporation
*
* SPDX-License-Identifier: Apache-2.0
*/
#include <device.h>
#include <devicetree.h>
#include <drivers/gpio.h>
#include <nrfx_twis.h>
#include <zephyr.h>
/* 1000 msec = 1 sec */
#define SLEEP_TIME_MS 1000
/* The devicetree node identifier for the "led0" alias. */
#define LED0_NODE DT_ALIAS(led0)
#if DT_NODE_HAS_STATUS(LED0_NODE, okay)
#define LED0 DT_GPIO_LABEL(LED0_NODE, gpios)
#define PIN DT_GPIO_PIN(LED0_NODE, gpios)
#define FLAGS DT_GPIO_FLAGS(LED0_NODE, gpios)
#else
/* A build error here means your board isn't set up to blink an LED. */
#error "Unsupported board: led0 devicetree alias is not defined"
#define LED0 ""
#define PIN 0
#define FLAGS 0
#endif
#define DEVICETREE_CONF true
#ifndef DEVICETREE_CONF
//nrfx driver configuration method
#define SLAVE_ADDR (0x28)
#define TWI_PIN_SDA 26
#define TWI_PIN_SCL 27
#define TWI_INT_PRIORITY 2
#else
//devicetree configuration method
static const uint32_t m_twis_addr0 = DT_REG_ADDR(DT_NODELABEL(twis_device1));
static const uint32_t m_twis_addr1 = DT_REG_ADDR(DT_NODELABEL(twis_device2));
static const uint32_t m_twis_sda_pin = DT_PROP(DT_NODELABEL(i2c0),sda_pin);
static const uint32_t m_twis_scl_pin = DT_PROP(DT_NODELABEL(i2c0),scl_pin);
static const uint8_t m_twis_prio = DT_IRQ(DT_NODELABEL(i2c0), priority);
#endif
// be sure TWI_BUFFER_SIZE matches master's tx buffer size.
#define TWI_BUFFER_SIZE 14
static unsigned char twis_rx_buffer[TWI_BUFFER_SIZE];
static unsigned char twis_tx_buffer[] = "This is a circular slave transmit buffer."; //length is whole number multiple of TWI_BUFFER_SIZE
static uint16_t buffer_index;
#define TWIS_INST 1
const nrfx_twis_t m_twis = NRFX_TWIS_INSTANCE(TWIS_INST);
static void twis_event_handler(nrfx_twis_evt_t const *const p_event) {
uint8_t incr = 0;
//printk("TWIS EVT handler\n");
switch (p_event->type) {
case NRFX_TWIS_EVT_READ_REQ:
//printk("\nTWIS EVT READ REQ\n");
if (p_event->data.buf_req) {
(void) nrfx_twis_tx_prepare(&m_twis,twis_tx_buffer + buffer_index, TWI_BUFFER_SIZE);
if((buffer_index += TWI_BUFFER_SIZE) >= sizeof(twis_tx_buffer)){
buffer_index = 0;
}
}
break;
case NRFX_TWIS_EVT_READ_DONE:
//printk("\nTWIS EVT READ DONE\n");
break;
case NRFX_TWIS_EVT_WRITE_REQ:
//printk("\nTWIS EVT WRITE REQ 1\n");
if (p_event->data.buf_req) {
//printk("\nTWIS EVT WRITE REQ 2\n");
(void)nrfx_twis_rx_prepare(&m_twis, twis_rx_buffer, sizeof(twis_rx_buffer));
}
break;
case NRFX_TWIS_EVT_WRITE_DONE:
printk("TWIS RX: ");
while(incr < TWI_BUFFER_SIZE) {
printk("%c", twis_rx_buffer[incr++]);
}
printk("\n");
break;
case NRFX_TWIS_EVT_READ_ERROR:
printk("\nTWIS READ ERROR\n");
break;
case NRFX_TWIS_EVT_WRITE_ERROR:
printk("\nTWIS WRITE ERROR\n");
break;
case NRFX_TWIS_EVT_GENERAL_ERROR:
printk("\nTWIS GENERAL ERROR\n");
break;
default:
printk("TWIS default\n");
break;
} // switch
}
void twis_init(void){
IRQ_CONNECT(DT_IRQN(DT_NODELABEL(i2c1)),
DT_IRQ(DT_NODELABEL(i2c1), priority),
nrfx_isr, nrfx_twis_1_irq_handler, 0);
#ifndef DEVICETREE_CONF
nrfx_twis_config_t config;
config.addr[0] = SLAVE_ADDR;
config.addr[1] = 0;
config.scl = TWI_PIN_SCL;
config.scl_pull = NRF_GPIO_PIN_PULLUP;
config.sda = TWI_PIN_SDA;
config.sda_pull = NRF_GPIO_PIN_PULLUP;
config.interrupt_priority = TWI_INT_PRIORITY;
#else
//devicetree configuration method
nrfx_twis_config_t dt_config;
dt_config.addr[0] = m_twis_addr0;
dt_config.addr[1] = m_twis_addr1;
dt_config.scl = m_twis_scl_pin;
dt_config.scl_pull = NRF_GPIO_PIN_PULLUP;
dt_config.sda = m_twis_sda_pin;
dt_config.sda_pull = NRF_GPIO_PIN_PULLUP;
dt_config.interrupt_priority = m_twis_prio;
#endif
printk("\nI2C Slave: ADDR: 0x%x, SCL: %d, SDA: %d, int_pri: %d",
dt_config.addr[0],
dt_config.scl,
dt_config.sda,
dt_config.interrupt_priority);
if(nrfx_twis_init(&m_twis, &dt_config, twis_event_handler) == NRFX_SUCCESS){
printk("\nnrfx twis initialized.\n\n");
}
else
printk("\nERROR: nrfx_twis_init()\n");
}
void main(void) {
const struct device *dev;
bool led_is_on = true;
uint32_t ret_code = NRFX_SUCCESS;
dev = device_get_binding(LED0);
if (dev == NULL) {
return;
}
ret_code = gpio_pin_configure(dev, PIN, GPIO_OUTPUT_ACTIVE | FLAGS);
if (ret_code < 0) {
return;
}
twis_init();
nrfx_twis_enable(&m_twis);
while (1) {
gpio_pin_set(dev, PIN, (int)led_is_on);
led_is_on = !led_is_on;
k_msleep(SLEEP_TIME_MS);
}
}IRQ_CONNECT(DT_IRQN(DT_NODELABEL(i2c0)),
DT_IRQ(DT_NODELABEL(i2c0), priority),
nrfx_isr, nrfx_twis_0_irq_handler, 0);| TWIM | TWIS | |
| GND | GND | GND |
| P0.31 | SCL | P0.27 |
| P0.30 | SDA | P0.26 |
Throughout both sets of the code, several printk statements have been commented out. You may want to uncomment any of these to assist in fully understanding the flow of the application.
There are a few TWI Test Configuration Options within main-twi.c, which should now be called main.c in the blinky-twim project.
ECHO WRITES: When set to false, each device will only print what it has received. By selecting this macro ECHO WRITES to true, the TWIM will also output the message it has written to the slave device.
MSG_EXCHANGE_CNT: The number of message exchanges to be sent between the TWIM and TWIS.
INFINITE_MSG_EXCHANGE: When set to true, the message exchange is continuous.
TWI_LOOPBACK: When set to true, the first message sent by the master will be “Begin Loopback.” The subsequent messages sent by the TWIS will be returned to the TWIS.
TWI_BUFFER_SIZE must be set to the same value in both main.c files to change the length of the exchange messages.c files.
The TWIS nRFX code was derived from RF5_SDK_17.0.2\examples\peripheral\twi_master_with_twis_slave (download nRF5 SDK 17.2).
A deep dive into the Zephyr 2.5 device model (I highly recommend viewing this video.)
Source Code
/*
* Copyright (c) 2016 Intel Corporation
*
* SPDX-License-Identifier: Apache-2.0
*/
#include <device.h>
#include <devicetree.h>
#include <drivers/gpio.h>
#include <nrfx_twis.h>
#include <zephyr.h>
/* 1000 msec = 1 sec */
#define SLEEP_TIME_MS 1000
/* The devicetree node identifier for the "led0" alias. */
#define LED0_NODE DT_ALIAS(led0)
#if DT_NODE_HAS_STATUS(LED0_NODE, okay)
#define LED0 DT_GPIO_LABEL(LED0_NODE, gpios)
#define PIN DT_GPIO_PIN(LED0_NODE, gpios)
#define FLAGS DT_GPIO_FLAGS(LED0_NODE, gpios)
#else
/* A build error here means your board isn't set up to blink an LED. */
#error "Unsupported board: led0 devicetree alias is not defined"
#define LED0 ""
#define PIN 0
#define FLAGS 0
#endif
#define DEVICETREE_CONF true
#ifndef DEVICETREE_CONF
//nrfx driver configuration method
#define SLAVE_ADDR (0x28)
#define TWI_PIN_SDA 26
#define TWI_PIN_SCL 27
#define TWI_INT_PRIORITY 2
#else
//devicetree configuration method
static const uint32_t m_twis_addr0 = DT_REG_ADDR(DT_NODELABEL(twis_device1));
static const uint32_t m_twis_addr1 = DT_REG_ADDR(DT_NODELABEL(twis_device2));
static const uint32_t m_twis_sda_pin = DT_PROP(DT_NODELABEL(i2c0),sda_pin);
static const uint32_t m_twis_scl_pin = DT_PROP(DT_NODELABEL(i2c0),scl_pin);
static const uint8_t m_twis_prio = DT_IRQ(DT_NODELABEL(i2c0), priority);
#endif
// be sure TWI_BUFFER_SIZE matches master's tx buffer size.
#define TWI_BUFFER_SIZE 14
static unsigned char twis_rx_buffer[TWI_BUFFER_SIZE];
static unsigned char twis_tx_buffer[] = "This is a circular slave transmit buffer."; //length is whole number multiple of TWI_BUFFER_SIZE
static uint16_t buffer_index;
#define TWIS_INST 1
const nrfx_twis_t m_twis = NRFX_TWIS_INSTANCE(TWIS_INST);
static void twis_event_handler(nrfx_twis_evt_t const *const p_event) {
uint8_t incr = 0;
//printk("TWIS EVT handler\n");
switch (p_event->type) {
case NRFX_TWIS_EVT_READ_REQ:
//printk("\nTWIS EVT READ REQ\n");
if (p_event->data.buf_req) {
(void) nrfx_twis_tx_prepare(&m_twis,twis_tx_buffer + buffer_index, TWI_BUFFER_SIZE);
if((buffer_index += TWI_BUFFER_SIZE) >= sizeof(twis_tx_buffer)){
buffer_index = 0;
}
}
break;
case NRFX_TWIS_EVT_READ_DONE:
//printk("\nTWIS EVT READ DONE\n");
break;
case NRFX_TWIS_EVT_WRITE_REQ:
//printk("\nTWIS EVT WRITE REQ 1\n");
if (p_event->data.buf_req) {
//printk("\nTWIS EVT WRITE REQ 2\n");
(void)nrfx_twis_rx_prepare(&m_twis, twis_rx_buffer, sizeof(twis_rx_buffer));
}
break;
case NRFX_TWIS_EVT_WRITE_DONE:
printk("TWIS RX: ");
while(incr < TWI_BUFFER_SIZE) {
printk("%c", twis_rx_buffer[incr++]);
}
printk("\n");
break;
case NRFX_TWIS_EVT_READ_ERROR:
printk("\nTWIS READ ERROR\n");
break;
case NRFX_TWIS_EVT_WRITE_ERROR:
printk("\nTWIS WRITE ERROR\n");
break;
case NRFX_TWIS_EVT_GENERAL_ERROR:
printk("\nTWIS GENERAL ERROR\n");
break;
default:
printk("TWIS default\n");
break;
} // switch
}
void twis_init(void){
IRQ_CONNECT(DT_IRQN(DT_NODELABEL(i2c1)),
DT_IRQ(DT_NODELABEL(i2c1), priority),
nrfx_isr, nrfx_twis_1_irq_handler, 0);
#ifndef DEVICETREE_CONF
nrfx_twis_config_t config;
config.addr[0] = SLAVE_ADDR;
config.addr[1] = 0;
config.scl = TWI_PIN_SCL;
config.scl_pull = NRF_GPIO_PIN_PULLUP;
config.sda = TWI_PIN_SDA;
config.sda_pull = NRF_GPIO_PIN_PULLUP;
config.interrupt_priority = TWI_INT_PRIORITY;
#else
//devicetree configuration method
nrfx_twis_config_t dt_config;
dt_config.addr[0] = m_twis_addr0;
dt_config.addr[1] = m_twis_addr1;
dt_config.scl = m_twis_scl_pin;
dt_config.scl_pull = NRF_GPIO_PIN_PULLUP;
dt_config.sda = m_twis_sda_pin;
dt_config.sda_pull = NRF_GPIO_PIN_PULLUP;
dt_config.interrupt_priority = m_twis_prio;
#endif
printk("\nI2C Slave: ADDR: 0x%x, SCL: %d, SDA: %d, int_pri: %d",
dt_config.addr[0],
dt_config.scl,
dt_config.sda,
dt_config.interrupt_priority);
if(nrfx_twis_init(&m_twis, &dt_config, twis_event_handler) == NRFX_SUCCESS){
printk("\nnrfx twis initialized.\n\n");
}
else
printk("\nERROR: nrfx_twis_init()\n");
}
void main(void) {
const struct device *dev;
bool led_is_on = true;
uint32_t ret_code = NRFX_SUCCESS;
dev = device_get_binding(LED0);
if (dev == NULL) {
return;
}
ret_code = gpio_pin_configure(dev, PIN, GPIO_OUTPUT_ACTIVE | FLAGS);
if (ret_code < 0) {
return;
}
twis_init();
nrfx_twis_enable(&m_twis);
while (1) {
gpio_pin_set(dev, PIN, (int)led_is_on);
led_is_on = !led_is_on;
k_msleep(SLEEP_TIME_MS);
}
}
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