tmc2208: Initial support for configuring TMC2208 drivers

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

config/example-extras.cfg

@@ -584,6 +584,59 @@
 #   to an appropriate sensitivity value.) The default is to not enable
 #   sensorless homing.
 
+# Configure a TMC2208 (or TMC2224) stepper motor driver via single
+# wire UART. To use this feature, define a config section with a
+# "tmc2208" prefix followed by the name of the corresponding stepper
+# config section (for example, "[tmc2208 stepper_x]").
+#[tmc2208 stepper_x]
+#uart_pin:
+#   The pin connected to the TMC2208 PDN_UART line. This parameter
+#   must be provided.
+#tx_pin:
+#   If using separate receive and transmit lines to communicate with
+#   the driver then set uart_pin to the receive pin and tx_pin to the
+#   transmit pin. The default is to use uart_pin for both reading and
+#   writing.
+#microsteps:
+#   The number of microsteps to configure the driver to use. Valid
+#   values are 1, 2, 4, 8, 16, 32, 64, 128, 256. This parameter must
+#   be provided.
+#interpolate: True
+#   If true, enable step interpolation (the driver will interally step
+#   at a rate of 256 micro-steps). The default is True.
+#run_current:
+#   The amount of current (in amps) to configure the driver to use
+#   during stepper movement. This parameter must be provided.
+#hold_current:
+#   The amount of current (in amps) to configure the driver to use
+#   when the stepper is not moving. The default is to use the same
+#   value as run_current.
+#sense_resistor: 0.110
+#   The resistance (in ohms) of the motor sense resistor. The default
+#   is 0.110 ohms.
+#stealthchop_threshold: 0
+#   The velocity (in mm/s) to set the "stealthChop" threshold to. When
+#   set, "stealthChop" mode will be enabled if the stepper motor
+#   velocity is below this value. The default is 0, which disables
+#   "stealthChop" mode.
+#driver_IHOLDDELAY: 8
+#driver_TPOWERDOWN: 20
+#driver_BLANK_TIME_SELECT: 2
+#driver_TOFF: 3
+#driver_HEND: 0
+#driver_HSTRT: 5
+#driver_PWM_AUTOGRAD: True
+#driver_PWM_AUTOSCALE: True
+#driver_PWM_LIM: 12
+#driver_PWM_REG: 8
+#driver_PWM_FREQ: 1
+#driver_PWM_GRAD: 14
+#driver_PWM_OFS: 36
+#   Set the given register during the configuration of the TMC2208
+#   chip. This may be used to set custom motor parameters. The
+#   defaults for each parameter are next to the parameter name in the
+#   above list.
+
 
 # Homing override. One may use this mechanism to run a series of
 # g-code commands in place of a G28 found in the normal g-code input.