Loopback wiring for tests¶

Overview¶

This shield is less a plug-on module in the conventional sense than more a wiring for feedback of certain signals. It can be used to run most test cases for Zephyr drivers that require a loopback connection on hardware level.

Requirements¶

This shield requires a board which provides a configuration that allows:

two GPIO lines, 1st for output and 2nd for loopback input
two PWM lines, 1st for output and 2nd for loopback input
one PWM line for output and one ADC line for input
one SPI interface, MOSI for output and MISO for input
two I2C interfaces, 1st for slave and 2nd for master mode
two UART interfaces, 1st for counterpart and 2nd for test case

Note

Sometimes boards declare standard headers like Arduino R3 but not define all connections. Make sure that the board you are using have all definitions to avoid build errors (see Shields for more details).

Supported variations¶

The below table suggests shield variation accordingly with test cases. When a standard connector (arduino, mikrobus, tmph) is available on board, user should select the matching shield configuration. When loopback_test shield is used with a board that doesn’t feature a standard connector, a dedicated <board>.overlay file should be provided. The remaining configurations should be used based on the board standard headers available.

Connector Standard	Shield Designation	Variation
Without standard (overlay)	loopback_test	1
Arduino R3 (not yet, planned)	loopback_test_arduino	2
MikroBus (not yet, planned)	loopback_test_mikrobus	3
TiaC MAGPIE Pin Header	loopback_test_tmph	4

Build and Programming¶

Set -DSHIELD=<shield designation> when you invoke west build.

To build shield with specific overlay:

west build -b tiac_magpie zephyr/tests/drivers/gpio/gpio_basic_api -- -DSHIELD=loopback_test
west flash

To build shield with standard headers:

west build -b [tiac_magpie | nucleo_f746zg] zephyr/tests/drivers/gpio/gpio_basic_api -- -DSHIELD=[loopback_test_arduino | loopback_test_mikrobus | loopback_test_tmph]
west flash

Wiring Schematics¶

Arduino R3

not yet, planned

MikroBus

not yet, planned

TiaC MAGPIE Pin Header

for test cases in tests/drivers/gpio
needs test fixture: gpio_loopback in hardware map

GPIO loopback¶

	gpio_basic_api_0 {
		compatible = "test,gpio_basic_api";
		out-gpios = <&tmph2 9 0>;	/* TMPH2:10 */
		in-gpios = <&tmph2 11 0>;	/* TMPH2:12 */
	}; // gpio_basic_api_0

out-gpios: Identity of a GPIO that will be configured as an output. This must be on the same device as in-gpios, and physically connected to in-gpios.
in-gpios: Identity of a GPIO that will be configured as an input. This must be on the same device as out-gpios, and physically connected to out-gpios.

for test cases in tests/drivers/pwm
needs test fixture: pwm_loopback in hardware map

PWM loopback¶

	pwm_loopback_0 {
		compatible = "test,pwm_loopback";
		/* channel 1 pwm out to channel 4 capture in */
		pwms = <&tmph_pwms 1 0 0>,	/* TMPH4:5 */
		       <&tmph_pwms 4 0 0>;	/* TMPH1:3 */
	}; // pwm_loopback_0

pwms: PWM pins that will be used for generating and capturing a pulse-width modulated signal. The pin at the first index will be used for signal generation while the pin at the second index will be used for capuring the generated signal. The two pins must be physically connected to each other.

PWM enable¶

&tmph_pwms {
	status = "okay";
}; // tmph_pwms

Timer enable¶

&tmph_timers {
	status = "okay";
}; // tmph_timers

for test cases in tests/drivers/spi
needs test fixture: spi_loopback in hardware map

SPI enable¶

&tmph_spi1 {
	status = "okay";
}; // tmph_spi1

for test cases in tests/drivers/i2c
needs test fixture: i2c_bus_short in hardware map

I2C one enable with EEPROM 1 as bus master¶

&tmph_i2c1 {
	status = "okay";

	eeprom1: eeprom@56 {
		compatible = "atmel,at24";
		reg = <0x56>;
		size = <1024>;
		pagesize = <16>;
		address-width = <8>;
		timeout = <5>;
		status = "okay";
		label = "EEPROM_1";
	}; // eeprom1
}; // tmph_i2c1

I2C two enable with EEPROM 0 as slave device¶

&tmph_i2c2 {
	status = "okay";

	eeprom0: eeprom@54 {
		compatible = "atmel,at24";
		reg = <0x54>;
		size = <1024>;
		pagesize = <16>;
		address-width = <8>;
		timeout = <5>;
		status = "okay";
		label = "EEPROM_0";
	}; // eeprom0
}; // tmph_i2c2

Transfer of commands from one bus controller to the other is accomplished by hardware through having the SCL (and SDA) signals shorted to join the two buses.