dac084S085: SPI DAC DAC084S085 implementation (#5134)

Alligator Board Rev2 tested config sample.
Add example configuration file for Alligator board rev.3.

Signed-off-by: Lorenzo Franco <lorenzo.franco@lorenzing.com>

klippy/extras/dac084S085.py

@@ -0,0 +1,25 @@
+# SPI DAC DAC084S085 implementation
+#
+# Copyright (C) 2021  Lorenzo Franco <lorenzo.franco@lorenzing.com>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+
+from . import bus
+
+class dac084S085:
+    def __init__(self, config):
+        self.spi = bus.MCU_SPI_from_config(
+            config, 1, pin_option="enable_pin", default_speed=10000000)
+        scale = config.getfloat('scale', 1., above=0.)
+        for chan, name in enumerate("ABCD"):
+            val = config.getfloat('channel_%s' % (name,), None,
+                                   minval=0., maxval=scale)
+            if val is not None:
+                self.set_register(chan, int(val * 255. / scale))
+    def set_register(self, chan, value):
+        b1 = (chan << 6) | (1 << 4) | ((value >> 4) & 0x0f)
+        b2 = (value << 4) & 0xf0
+        self.spi.spi_send([b1, b2])
+
+def load_config_prefix(config):
+    return dac084S085(config)