mcp4451: Add initial support for programming the mcp4451 on lpc176x

Add support for programming smoothieboard current.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/mcp4451.py

@@ -0,0 +1,32 @@
+# MCP4451 digipot code
+#
+# Copyright (C) 2018  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+import mcu
+
+WiperRegisters = [0x00, 0x01, 0x06, 0x07]
+
+class mcp4451:
+    def __init__(self, config):
+        printer = config.get_printer()
+        self.mcu = mcu.get_printer_mcu(printer, config.get('mcu', 'mcu'))
+        self.i2c_addr = config.getint('i2c_address')
+        scale = config.getfloat('scale', 1., above=0.)
+        wipers = [None]*4
+        for i in range(len(wipers)):
+            val = config.getfloat('wiper_%d' % (i,), None,
+                                  minval=0., maxval=scale)
+            if val is not None:
+                wipers[i] = int(val * 255. / scale + .5)
+        self.add_config_cmd(0x04, 0xff)
+        self.add_config_cmd(0x0a, 0xff)
+        for reg, val in zip(WiperRegisters, wipers):
+            if val is not None:
+                self.add_config_cmd(reg, val)
+    def add_config_cmd(self, reg, val):
+        self.mcu.add_config_cmd("i2c_send data=%02x%02x%02x" % (
+            self.i2c_addr, (reg << 4) | ((val >> 8) & 0x03), val), is_init=True)
+
+def load_config_prefix(config):
+    return mcp4451(config)