FPGA test: Add ReadMe file

Author: jeromecoutant

TESTS/mbed_hal_fpga_ci_test_shield/README.md

@@ -0,0 +1,51 @@
+# Testing with FPGA CI TEST shield
+
+## Setup
+
+![30% center](fpga_test_shield.jpg)
+
+```
+mbed test -n tests*fpga* --app-config tests/configs/fpga.json
+```
+
+FPGA_CI_TEST_SHIELD needed macro  
+and specific test capabilities per target  
+are defined in:  
+https://github.com/ARMmbed/mbed-os/blob/master/TESTS/configs/fpga.json
+
+
+
+## MBED-OS
+
+Tested from factor is defined by MBED_CONF_TARGET_DEFAULT_FORM_FACTOR  
+"default-form-factor" default value is null.
+
+When "default-form-factor" is not set, ARDUINO form factor is used.
+
+Default ff_arduino_pins is defined in:
+https://github.com/ARMmbed/mbed-os/blob/master/hal/mbed_pinmap_default.cpp#L28-L32
+
+Default ff_arduino_names is defined in:
+https://github.com/ARMmbed/mbed-os/blob/master/hal/mbed_pinmap_default.cpp#L34-L38
+
+Default empty_gpio_pinmap is defined in:
+https://github.com/ARMmbed/mbed-os/blob/master/hal/mbed_gpio.c#L89-L114
+
+Some pins are restricted:
+https://github.com/ARMmbed/mbed-os/blob/master/hal/mbed_pinmap_default.cpp#L69-L73
+
+Some peripherals are restricted:
+https://github.com/ARMmbed/mbed-os/blob/master/hal/mbed_pinmap_default.cpp#L94-L100
+
+
+## Known issues
+
+
+## LINKS
+
+https://github.com/ARMmbed/fpga-ci-test-shield
+
+https://github.com/ARMmbed/fpga-ci-test-shield-updater
+
+https://github.com/ARMmbed/fpga-ci-test-shield-terminal
+