tests/run-tests.py: Add support for board-specific target_wiring config.

There are currently a few "hardware" tests that need external board
connections to be made for them to work, such as bridging a pair of pins.
For example, all tests in `tests/extmod_hardware` need some kind of
connection.

Along with the physical connections -- which are different for each board
-- there needs to be corresponding Python settings, eg which UART instance
to use and which pins for TX/RX.

These settings are currently hard-coded in each test file. That has a few
problems:
- settings are repeated, eg all the UART tests have pretty much the same
  settings code duplicated across them
- changing the settings means changing many files
- adding a new board means adding a lot of code
- the tests get bigger and bigger with each new board that they support,
  meaning they may not fit on targets with a small amount of RAM (that's
  already the case with `tests/extmod_hardware/machine_pwm.py`)
- if you have a custom board you have to manually edit the test to add your
  own settings

This commit aims to solve all the above problems by splitting the board-
specific settings out into separate files, one for each board (or port).
They are placed in the `tests/target_wiring/` directory.  The
`run-tests.py` test runner then loads the appropriate configuration for the
target that is being tested, sends it to the board so it's available as
`import target_wiring` (without needing a filesystem), and then executes
the test.  Note tht only tests that need `target_wiring` have it loaded.

This commit adds support for this `target_wiring` scheme.

Signed-off-by: Damien George <damien@micropython.org>

tests/run-tests.py

@@ -216,6 +216,9 @@ platform_tests_to_skip = {
     ),
 }
 
+# Tests that require `import target_wiring` to work.
+tests_requiring_target_wiring = ()
+
 
 def rm_f(fname):
     if os.path.exists(fname):
@@ -310,6 +313,7 @@ def detect_test_platform(pyb, args):
     args.float_prec = float_prec
     args.unicode = unicode
 
+    # Print the detected information about the target.
     print("platform={}".format(platform), end="")
     if arch:
         print(" arch={}".format(arch), end="")
@@ -321,7 +325,43 @@ def detect_test_platform(pyb, args):
         print(" float={}-bit".format(float_prec), end="")
     if unicode:
         print(" unicode", end="")
-    print()
+
+
+def detect_target_wiring_script(pyb, args):
+    tw_data = b""
+    tw_source = None
+    if args.target_wiring:
+        # A target_wiring path is explicitly provided, so use that.
+        tw_source = args.target_wiring
+        with open(tw_source, "rb") as f:
+            tw_data = f.read()
+    elif hasattr(pyb, "exec_raw") and pyb.exec_raw("import target_wiring") == (b"", b""):
+        # The board already has a target_wiring module available, so use that.
+        tw_source = "on-device"
+    else:
+        port = platform_to_port(args.platform)
+        build = args.build
+        tw_board_exact = None
+        tw_board_partial = None
+        tw_port = None
+        for file in os.listdir("target_wiring"):
+            file_base = file.removesuffix(".py")
+            if file_base == build:
+                # A file matching the target's board/build name.
+                tw_board_exact = file
+            elif file_base.endswith("x") and build.startswith(file_base.removesuffix("x")):
+                # A file with a partial match to the target's board/build name.
+                tw_board_partial = file
+            elif file_base == port:
+                # A file matching the target's port.
+                tw_port = file
+        tw_source = tw_board_exact or tw_board_partial or tw_port
+        if tw_source:
+            with open("target_wiring/" + tw_source, "rb") as f:
+                tw_data = f.read()
+    if tw_source:
+        print(" target_wiring={}".format(tw_source), end="")
+    pyb.target_wiring_script = tw_data
 
 
 def prepare_script_for_target(args, *, script_text=None, force_plain=False):
@@ -382,6 +422,12 @@ def run_script_on_remote_target(pyb, args, test_file, is_special):
     try:
         had_crash = False
         pyb.enter_raw_repl()
+        if test_file.endswith(tests_requiring_target_wiring) and pyb.target_wiring_script:
+            pyb.exec_(
+                "import sys;sys.modules['target_wiring']=__build_class__(lambda:exec("
+                + repr(pyb.target_wiring_script)
+                + "),'target_wiring')"
+            )
         output_mupy = pyb.exec_(script, timeout=TEST_TIMEOUT)
     except pyboard.PyboardError as e:
         had_crash = True
@@ -1285,6 +1331,11 @@ the last matching regex is used:
         default=None,
         help="prologue python file to execute before module import",
     )
+    cmd_parser.add_argument(
+        "--target-wiring",
+        default=None,
+        help="force the given script to be used as target_wiring.py",
+    )
     args = cmd_parser.parse_args()
 
     prologue = ""
@@ -1381,6 +1432,13 @@ the last matching regex is used:
         # tests explicitly given
         tests = args.files
 
+    # If any tests need it, prepare the target_wiring script for the target.
+    if pyb and any(test.endswith(tests_requiring_target_wiring) for test in tests):
+        detect_target_wiring_script(pyb, args)
+
+    # End the target information line.
+    print()
+
     if not args.keep_path:
         # Clear search path to make sure tests use only builtin modules, those in
         # extmod, and a path to unittest in case it's needed.