atmel-samd: Introduce a nvm module for non-volatile byte-level memory access. (#203)

* atmel-samd: Introduce a nvm module for non-volatile byte-level memory access.

This allows for persisting small configuration values even when the file system
is read-only from CircuitPython.

Fixes #160

* Review feedback:
* Add tests.
* Fix non-zero index.
* Fix len()

3 files changed, 39 insertions, 0 deletions

diff --git a/tests/circuitpython/nvm_not_present.py b/tests/circuitpython/nvm_not_present.py
new file mode 100644
index 000000000..141e60b01
--- /dev/null
+++ b/tests/circuitpython/nvm_not_present.py
@@ -0,0 +1,6 @@
+import skip_if
+skip_if.board_not_in("gemma_m0", "trinket_m0")
+
+import microcontroller
+
+assert(microcontroller.nvm == None)
diff --git a/tests/circuitpython/nvm_present.py b/tests/circuitpython/nvm_present.py
new file mode 100644
index 000000000..a2cf3a22c
--- /dev/null
+++ b/tests/circuitpython/nvm_present.py
@@ -0,0 +1,22 @@
+import skip_if
+skip_if.board_not_in("metro_m0_express", "feather_m0_express", "circuitplayground_express")
+
+import microcontroller
+import random
+nvm = microcontroller.nvm
+
+len(nvm)
+
+single = random.randint(0, 255)
+nvm[1] = single
+assert(nvm[1] == single)
+
+nvm[0] = single
+assert(nvm[0] == single)
+
+b = bytearray()
+for i in range(10):
+    b.append(random.randint(0, 255))
+
+microcontroller.nvm[10:20] = b
+assert(microcontroller.nvm[10:20] == b)
diff --git a/tests/skip_if.py b/tests/skip_if.py
index f6d22b4c1..7b1e06871 100644
--- a/tests/skip_if.py
+++ b/tests/skip_if.py
@@ -52,6 +52,17 @@ def board_in(*board):
     if test_env.board in board:
         skip()
 
+def board_not_in(*board):
+    try:
+        import test_env
+    except ImportError:
+        class Env:
+            def __init__(self, board):
+                self.board = board
+        test_env = Env("unknown")
+    if test_env.board not in board:
+        skip()
+
 def no_cpython_compat():
     try:
         try: