tests/periph/selftest_shield: add test application

This test application makes use of the RIOT Peripheral Selftest Shield,
which connects e.g. PWM to ADC or SPI MOSI to SPI MISO, UART TXD to RXD,
etc. This provides quick and fully automated self testing capabilities.

Please note that the simplicity and ease of use of the hardware comes
with a prices: There are whole classes of issues that cannot be detected
automatically. This test cannot replace other testing approaches
(such as manual testing or PHiLIP on the HiL), but only complement them.

tests/periph/selftest_shield/Makefile

@@ -0,0 +1,32 @@
+BOARD ?= arduino-due
+
+include ../Makefile.periph_common
+
+FEATURES_REQUIRED += arduino_pins
+FEATURES_REQUIRED += arduino_shield_uno
+
+FEATURES_OPTIONAL += arduino_analog
+FEATURES_OPTIONAL += arduino_i2c
+FEATURES_OPTIONAL += arduino_pwm
+FEATURES_OPTIONAL += arduino_shield_isp
+FEATURES_OPTIONAL += arduino_spi
+FEATURES_OPTIONAL += arduino_uart
+FEATURES_OPTIONAL += periph_adc
+FEATURES_OPTIONAL += periph_gpio
+FEATURES_OPTIONAL += periph_gpio_irq
+FEATURES_OPTIONAL += periph_i2c
+FEATURES_OPTIONAL += periph_pwm
+FEATURES_OPTIONAL += periph_spi
+FEATURES_OPTIONAL += periph_timer
+FEATURES_OPTIONAL += periph_uart
+
+include $(RIOTBASE)/Makefile.include
+
+ifneq ($(MCU),esp32)
+  # We only need 2 threads (+ the Idle thread on some platforms) and we really
+  # want this app working on as many boards as possible
+  CFLAGS += -DMAXTHREADS=3
+else
+  # ESP32x SoCs uses an extra thread for esp_timer
+  CFLAGS += -DMAXTHREADS=4
+endif

tests/periph/selftest_shield/Makefile.board.dep

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+ifneq (,$(filter periph_i2c,$(FEATURES_USED)))
+  ifneq (,$(filter arduino_i2c,$(FEATURES_USED)))
+    USEMODULE += pcf8574
+  endif
+endif

tests/periph/selftest_shield/README.md

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+# Peripheral Test Battery using the Peripheral Selftest Shield
+
+This test application does a full self test of any of the following peripheral
+driver, if supported by the board and Arduino I/O mapping is available:
+
+- `periph_adc` (1)
+- `periph_gpio`
+- `periph_gpio_irq`
+- `periph_i2c` (2)
+- `periph_pwm`
+- `periph_spi` (3)
+- `periph_uart` (4)
+
+Notes:
+1. The ADC input is generated via a 4-bit R-2R resistor ladder and the I2C
+   attached GPIO extender and/or PWM. If neither is available, no tests are
+   performed. If both are available, up to three ADC channels are tested:
+   Those muxed to pins A0, A1, and A2.
+2. I2C is indirectly tested by operating the PCF8574 I2C GPIO extender and
+   observing the result using internal GPIOs connected to the external ones.
+   This test is only enabled if both `periph_i2c` and `periph_gpio` is
+   available
+3. Correctness of the clock frequency, clock phase and clock polarity is not
+   checked due to the limitations of the selftest shield.
+4.  UART self testing is skipped when the D0/D1 UART interface is used for
+    stdio. In addition, correctness of the symbol rate (often incorrectly
+    referred to as "baudrate") cannot be tested, as bugs here would affect
+    both TX and RX in the same way and negate each other.
+
+## Configuration
+
+The test requires no configuration and will by default test all of the above
+peripheral drivers for which Arduino I/O mappings exists. To disable a subset
+of the tests (e.g. to safe RAM/ROM to trim down the test to a low end board), it
+is possible to disable features (`FEATURES_BLACKLIST += periph_<foobar>`).