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tests: drivers: uart: baudrate_test: Improve accuracy measurement #28455

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Merged
nordic-piks merged 2 commits into from
May 4, 2026
Merged

tests: drivers: uart: baudrate_test: Improve accuracy measurement #28455

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398b0ea
tests: drivers: uart: baudrate_test: Cleanup
nordic-krch Apr 29, 2026
a24ca61
tests: drivers: uart: baudrate_test: Improve accuracy measurement
nordic-krch Apr 29, 2026
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2 changes: 1 addition & 1 deletion tests/drivers/uart/uart_baudrate_test/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ source "Kconfig.zephyr"

config TEST_ALLOWED_DEVIATION
int "Allowed deviation (%) for UART timing checks"
default 25
default 5
range 0 100
help
Maximum allowed deviation (%) from the programmed values for the test to be
Expand Down
115 changes: 57 additions & 58 deletions tests/drivers/uart/uart_baudrate_test/src/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -10,19 +10,24 @@
#include <zephyr/kernel.h>
#include <zephyr/ztest.h>
#include <zephyr/drivers/gpio.h>
#include <hal/nrf_gpio.h>
#include <stdlib.h>
#include <math.h>


static NRF_GPIO_Type *gpio_port =
((NRF_GPIO_Type *)DT_REG_ADDR(DT_GPIO_CTLR(DT_PATH(zephyr_user), gpios)));
static uint32_t pin_mask = BIT(DT_GPIO_PIN(DT_PATH(zephyr_user), gpios));
static const struct gpio_dt_spec gpio_spec =
GPIO_DT_SPEC_GET_BY_IDX(DT_PATH(zephyr_user), gpios, 0);
static const struct device *const uart_dev = DEVICE_DT_GET(DT_NODELABEL(dut));

static const uint8_t tx_buf[1] = {0x00};
static const uint8_t tx_buf[] = {0x00, 0x00};

#define PIN_STATE_SIZE 16384
static int pin_state[PIN_STATE_SIZE] = {};
#define PIN_STATE_SIZE 32768
static uint8_t pin_state[PIN_STATE_SIZE] = {};

#define REPEAT_NUMBER 10
#define REPEAT_NUMBER 3

#ifdef CONFIG_UART_INTERRUPT_DRIVEN
static void uart_fifo_callback(const struct device *dev, void *user_data)
Expand All @@ -43,7 +48,7 @@ static void uart_fifo_callback(const struct device *dev, void *user_data)
}
#endif

static void check_timing(const struct gpio_dt_spec *gpio_dt, uint32_t baudrate)
static void check_timing(uint32_t baudrate)
{
uint64_t cycles_s_sys;
struct uart_config test_uart_config;
Expand All @@ -53,16 +58,18 @@ static void check_timing(const struct gpio_dt_spec *gpio_dt, uint32_t baudrate)
double gpio_read_time_us_mean;
int32_t start_index;
int32_t stop_index;
int32_t idle_found;
int32_t start_index_count_zero;
double bit_diviation_mean;
double symbol_diviation_mean;
bool once = true;
int key;

ret = uart_config_get(uart_dev, &test_uart_config);
zassert_equal(ret, 0, "uart_config_get: %d\n", ret);

test_uart_config.parity = UART_CFG_PARITY_EVEN;
test_uart_config.stop_bits = UART_CFG_STOP_BITS_2;
test_uart_config.stop_bits = UART_CFG_STOP_BITS_1;
test_uart_config.flow_ctrl = UART_CFG_FLOW_CTRL_NONE;
test_uart_config.baudrate = baudrate;
ret = uart_configure(uart_dev, &test_uart_config);
Expand All @@ -75,37 +82,11 @@ static void check_timing(const struct gpio_dt_spec *gpio_dt, uint32_t baudrate)
cycles_s_sys = (uint64_t)sys_clock_hw_cycles_per_sec();
TC_PRINT("Cycles: %llu cycles\n", cycles_s_sys);

/*
* Measure time needed to read gpios
*/
gpio_read_time_us_mean = 0;
key = irq_lock();
for (uint32_t t = 0; t < REPEAT_NUMBER; ++t) {
cycle_start_time = k_cycle_get_32();
for (uint32_t i = 0; i < PIN_STATE_SIZE; ++i) {
pin_state[i] = gpio_pin_get_dt(&gpio_spec);
}
cycle_stop_time = k_cycle_get_32();
double gpio_read_time_us =
((cycle_stop_time - cycle_start_time) / (double)PIN_STATE_SIZE) *
(1e6 / cycles_s_sys);
gpio_read_time_us_mean += gpio_read_time_us;
}
irq_unlock(key);
gpio_read_time_us_mean /= (double)REPEAT_NUMBER;
TC_PRINT("GPIO get takes: %.2f us\n", gpio_read_time_us_mean);

double expected_bit_period_us = 1e6 / (double)baudrate;
double number_of_bits = 8;

number_of_bits += 1;
if (test_uart_config.stop_bits == UART_CFG_STOP_BITS_1) {
number_of_bits += 1;
} else if (test_uart_config.stop_bits == UART_CFG_STOP_BITS_2) {
number_of_bits += 2;
} else {
zassert_true(false, "Unsupported stop_bits: %d", test_uart_config.stop_bits);
}
/* Stop bit is 1 so it is not counted. */
if (test_uart_config.parity != UART_CFG_PARITY_NONE) {
number_of_bits += 1;
}
Expand All @@ -114,11 +95,6 @@ static void check_timing(const struct gpio_dt_spec *gpio_dt, uint32_t baudrate)
TC_PRINT("[%d] Expected symbol time: %.2f us, expected bit time: %.2f us\n", baudrate,
expected_symbol_period_us, expected_bit_period_us);

if (expected_bit_period_us < gpio_read_time_us_mean) {
TC_PRINT("[%d] Not supported - gpio measurement is too slow.\n", baudrate);
ztest_test_skip();
}

start_index_count_zero = 0;
bit_diviation_mean = 0;
symbol_diviation_mean = 0;
Expand All @@ -136,26 +112,49 @@ static void check_timing(const struct gpio_dt_spec *gpio_dt, uint32_t baudrate)
/*
* Check gpio
*/

key = irq_lock();
cycle_start_time = k_cycle_get_32();
for (uint32_t i = 0; i < PIN_STATE_SIZE; ++i) {
pin_state[i] = gpio_pin_get_dt(&gpio_spec);
pin_state[i] = nrf_gpio_port_in_read(gpio_port) & pin_mask ? 1 : 0;
}
cycle_stop_time = k_cycle_get_32();
irq_unlock(key);

if (once) {
/* Calculate only for the first iteration. */
uint32_t t_us = k_cyc_to_us_ceil32(cycle_stop_time - cycle_start_time);

gpio_read_time_us_mean = (double)t_us / PIN_STATE_SIZE;
once = false;
TC_PRINT("GPIO get takes: %.2f us\n", gpio_read_time_us_mean);
}

if (expected_bit_period_us < gpio_read_time_us_mean) {
TC_PRINT("[%d] Not supported - gpio measurement is too slow.\n", baudrate);
ztest_test_skip();
}

/*
* Find start of start bit and end of stop bit
* Find start of start bit and end of stop bit. For higher baudrates it is
* possible that first byte is already being transferred. In search for
* byte start and end, start from searching for idle state between byte 0 and 1.
*/
start_index = -1;
stop_index = -1;
idle_found = -1;
for (uint32_t i = 0; i < PIN_STATE_SIZE; ++i) {
if (-1 == start_index) {
if (0 == pin_state[i]) {
if (1 == pin_state[i]) {
idle_found = 0;
} else if ((idle_found == 0) && (0 == pin_state[i])) {
start_index = i;
}
} else {
if (-1 == stop_index) {
if (1 == pin_state[i]) {
stop_index = i;
break;
}
} else {
zassert_true(1 == pin_state[i], "Unexpected low at %d\n",
Expand Down Expand Up @@ -209,86 +208,86 @@ static void check_timing(const struct gpio_dt_spec *gpio_dt, uint32_t baudrate)

ZTEST(uart_baudrate_test, test_08_2400)
{
check_timing(&gpio_spec, 2400);
check_timing(2400);
}

ZTEST(uart_baudrate_test, test_09_4800)
{
check_timing(&gpio_spec, 4800);
check_timing(4800);
}

ZTEST(uart_baudrate_test, test_10_9600)
{
check_timing(&gpio_spec, 9600);
check_timing(9600);
}

ZTEST(uart_baudrate_test, test_11_14400)
{
check_timing(&gpio_spec, 14400);
check_timing(14400);
}
ZTEST(uart_baudrate_test, test_12_19200)
{
check_timing(&gpio_spec, 19200);
check_timing(19200);
}

ZTEST(uart_baudrate_test, test_13_38400)
{
check_timing(&gpio_spec, 38400);
check_timing(38400);
}

ZTEST(uart_baudrate_test, test_14_57600)
{
check_timing(&gpio_spec, 57600);
check_timing(57600);
}

ZTEST(uart_baudrate_test, test_15_115200)
{
check_timing(&gpio_spec, 115200);
check_timing(115200);
}

ZTEST(uart_baudrate_test, test_16_230400)
{
check_timing(&gpio_spec, 230400);
check_timing(230400);
}

ZTEST(uart_baudrate_test, test_17_460800)
{
check_timing(&gpio_spec, 460800);
check_timing(460800);
}

ZTEST(uart_baudrate_test, test_18_576000)
{
check_timing(&gpio_spec, 576000);
check_timing(576000);
}

ZTEST(uart_baudrate_test, test_19_921600)
{
check_timing(&gpio_spec, 921600);
check_timing(921600);
}

ZTEST(uart_baudrate_test, test_20_1000000)
{
check_timing(&gpio_spec, 1000000);
check_timing(1000000);
}

ZTEST(uart_baudrate_test, test_21_2000000)
{
check_timing(&gpio_spec, 2000000);
check_timing(2000000);
}

ZTEST(uart_baudrate_test, test_22_3000000)
{
check_timing(&gpio_spec, 3000000);
check_timing(3000000);
}

ZTEST(uart_baudrate_test, test_23_4000000)
{
check_timing(&gpio_spec, 4000000);
check_timing(4000000);
}

ZTEST(uart_baudrate_test, test_24_8000000)
{
check_timing(&gpio_spec, 8000000);
check_timing(8000000);
}

static void *uart_baudrate_test_setup(void)
Expand Down
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