extmod/machine_signal: Implement "signal" abstraction for machine module.

A signal is like a pin, but ca also be inverted (active low). As such, it
abstracts properties of various physical devices, like LEDs, buttons,
relays, buzzers, etc. To instantiate a Signal:

pin = machine.Pin(...)
signal = machine.Signal(pin, inverted=True)

signal has the same .value() and __call__() methods as a pin.

1 files changed, 1 insertions, 0 deletions

diff --git a/py/py.mk b/py/py.mk
index 94265c3f44..e7e4fb9b78 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -222,6 +222,7 @@ PY_O_BASENAME = \
 	../extmod/virtpin.o \
 	../extmod/machine_mem.o \
 	../extmod/machine_pinbase.o \
+	../extmod/machine_signal.o \
 	../extmod/machine_pulse.o \
 	../extmod/machine_i2c.o \
 	../extmod/machine_spi.o \