docs: Add Firmware_Commands.md with information on common firmware commands

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

2 files changed, 271 insertions, 1 deletions

diff --git a/docs/Firmware_Commands.md b/docs/Firmware_Commands.md
new file mode 100644
index 00000000..2416eb3c
--- /dev/null
+++ b/docs/Firmware_Commands.md
@@ -0,0 +1,268 @@
+This document provides high-level information on common firmware
+commands. It is not an authoritative reference for these commands, nor
+is it an exclusive list of all available firmware commands.
+
+This document may be useful for users needing to configure a set of
+hardware actions that their printer may require at startup (via the
+"custom" field in the printer config file), and it may be useful for
+developers wishing to obtain a high-level feel for available firmware
+commands.
+
+See the [protocol](Protocol.md) document for more information on the
+format of commands and their low-level transmission. The commands here
+are described using their "printf" style syntax - for those unfamiliar
+with that format, just note that where a '%...' sequence is seen it
+should be replaced with an actual integer.
+
+Startup Commands
+================
+
+It may be necessary to take certain one-time actions to configure the
+micro-controller and its peripherals. This section lists common
+commands available for that purpose. Unlike other firmware commands,
+these commands run as soon as they are received by the firmware and
+they do not require any particular setup.
+
+These commands are most useful in the "custom" block of the "mcu"
+section of the printer configuration file. This feature is typically
+used to configure the initial settings of LEDs, to configure
+micro-stepping pins, to configure a digipot, etc.
+
+Several of these commands will take a "pin=%u" parameter. The
+low-level firmware uses integer encodings of the hardware pin numbers,
+but to make things more readable the host will translate human
+readable pin names (eg, "PA3") to their equivalent integer
+encodings. By convention, any parameter named "pin" or that has a
+"_pin" suffix will use pin name translation by the host.
+
+Common startup commands:
+
+* set_digital_out pin=%u value=%c : This command immediately
+  configures the given pin as a digital out GPIO and it sets it to
+  either a low level (value=0) or a high level (value=1). This command
+  may be useful for configuring the initial value of LEDs and for
+  configuring the initial value of stepper driver micro-stepping pins.
+
+* set_pwm_out pin=%u cycle_ticks=%u value=%c : This command will
+  immediately configure the given pin to use hardware based
+  pulse-width-modulation (PWM) with the given number of
+  cycle_ticks. The "cycle_ticks" is the amount of time (in MCU clock
+  ticks) in a complete power on and power off cycle. A cycle_ticks
+  value of 1 can be used to request the fastest possible cycle
+  time. The specified "value" is between 0 and 255 with 0 indicating a
+  full off state and 255 indicating a full on state. This command may
+  be useful for enabling CPU and nozzle cooling fans.
+
+* send_spi_message pin=%u msg=%*s : This command can be used to
+  transmit messages to a serial-peripheral-interface (SPI) component
+  connected to the micro-controller. It has been used to configure the
+  startup settings of AD5206 digipots. The 'pin' parameter specifies
+  the chip select line to use during the transmission. The 'msg'
+  indicates the binary message to transmit to the given chip.
+
+Firmware configuration
+======================
+
+Most commands in the firmware require an initial setup before they can
+be successfully invoked. This section provides a high-level overview
+of the micro-controller configuration process. This section and the
+following sections are likely only of interest to developers
+interested in the internal details of Klipper.
+
+When the host first connects to the firmware it always starts by
+obtaining the firmware's data dictionary (see [protocol](Protocol.md)
+for more information). After the data dictionary is obtained the host
+will check if the firmware is in a "configured" state and configure it
+if not. Configuration involves the following phases:
+
+* get_config : The host starts by checking if the firmware is already
+  configured. The firmware responds to this command with a "config"
+  response message. At micro-controller power-on the firmware always
+  starts in an unconfigured state. It remains in this state until the
+  host completes the configuration processes (by issuing a
+  finalize_config command). If the firmware is already configured (and
+  is configured with the desired settings) from a previous
+  host/firmware session then no further action is needed by the host
+  and the configuration process ends successfully.
+
+* allocate_oids count=%c : This command is issued to inform the
+  firmware the maximum number of object-ids (oid) that the host
+  requires. It is only valid to issue this command once. An oid is an
+  integer identifier allocated to each stepper, each endstop, and each
+  schedulable gpio pin. The host determines in advance the number of
+  oids it will require to operate the hardware and passes this to the
+  firmware so that the firmware may allocate sufficient memory to
+  store a mapping from oid to internal firmware object.
+
+* config_XXX oid=%c ... : By convention any command starting with the
+  "config_" prefix creates a new firmware object and assigns the given
+  oid to it. For example, the config_digital_out command will
+  configure the specified pin as a digital output GPIO and create an
+  internal object that the host can use to schedule changes to the
+  given GPIO. The oid parameter passed into the config command is
+  selected by the host and must be between zero and the maximum count
+  supplied in the allocate_oids command. The config commands may only
+  be run when the firmware is not in a configured state (ie, prior to
+  the host sending finalize_config) and after the allocate_oids
+  command has been sent.
+
+* finalize_config crc=%u : The finalize_config command transitions the
+  firmware from an unconfigured state to a configured state. The crc
+  parameter passed to the firmware is stored in the firmware and
+  provided back to the host in "config" response messages. By
+  convention, the host takes a 32bit CRC of the firmware configuration
+  it will request and at the start of subsequent host/firmware
+  communication sessions it checks that the CRC stored in the firmware
+  exactly matches its desired CRC. If the CRC does not match then the
+  host knows the firmware has not been configured in the state desired
+  by the host.
+
+Common firmware objects
+-----------------------
+
+This section lists some commonly used config commands.
+
+* config_digital_out oid=%c pin=%u default_value=%c max_duration=%u :
+  This command creates an internal firmware object for the given GPIO
+  'pin'. The pin will be configured in digital output mode and set to
+  an initial value as specified by 'default_value' (0 for low, 1 for
+  high). Creating a digital_out object allows the host to schedule
+  GPIO updates for the given pin at specified times (see the
+  schedule_digital_out command described below). Should the firmware
+  go into shutdown mode then all configured digital_out objects will
+  be set back to their default values. The 'max_duration' parameter is
+  used to implement a safety check - if it is non-zero then it is the
+  maximum number of clock ticks that the host may set the given GPIO
+  to a non-default value without further updates. For example, if the
+  default_value is zero and the max_duration is 16000 then if the host
+  sets the gpio to a value of one then it must schedule another update
+  to the gpio pin (to either zero or one) within 16000 clock
+  ticks. This safety feature can be used with heater pins to ensure
+  the host does not set the heater to a value of one and then go
+  off-line.
+
+* config_pwm_out oid=%c pin=%u cycle_ticks=%u default_value=%c
+  max_duration=%u : This command creates an internal object for
+  hardware based PWM pins that the host may schedule updates for. Its
+  usage is analogous to config_digital_out - see the description of
+  the 'set_pwm_out' and 'config_digital_out' commands for parameter
+  description.
+
+* config_soft_pwm_out oid=%c pin=%u cycle_ticks=%u default_value=%c
+  max_duration=%u : This command creates an internal firmware object
+  for software implemented PWM. Unlike hardware pwm pins, a software
+  pwm object does not require any special hardware support (other than
+  the ability to configure the pin as a digital output GPIO). Because
+  the output switching is implemented in the software of the firmware,
+  it is recommended that the cycle_ticks parameter correspond to a
+  time of 10ms or greater. See the description of the 'set_pwm_out'
+  and 'config_digital_out' commands for parameter description.
+
+* config_analog_in oid=%c pin=%u : This command is used to configure a
+  pin in analog input sampling mode. Once configured, the pin can be
+  sampled at regular interval using the query_analog_in command (see
+  below).
+
+* config_stepper oid=%c step_pin=%c dir_pin=%c min_stop_interval=%u
+  invert_step=%c : This command creates an internal stepper
+  object. The 'step_pin' and 'dir_pin' parameters specify the step and
+  direction pins respectively; this command will configure them in
+  digital output mode. The 'invert_step' parameter specifies whether a
+  step occurs on a rising edge (invert_step=0) or falling edge
+  (invert_step=1). The 'min_stop_interval' implements a safety
+  feature - it is checked when the firmware finishes all moves for a
+  stepper - if it is non-zero it specifies the minimum number of clock
+  ticks since the last step. It is used as a check on the maximum
+  stepper velocity that a stepper may have before stopping.
+
+* config_end_stop oid=%c pin=%c pull_up=%c stepper_oid=%c : This
+  command creates an internal "endstop" object. It is used to specify
+  the endstop pins and to enable "homing" operations (see the
+  end_stop_home command below). The command will configure the
+  specified pin in digital input mode. The 'pull_up' parameter
+  determines whether hardware provided pullup resistors for the pin
+  (if available) will be enabled. The 'stepper_oid' parameter
+  specifies the oid of an associated stepper for the given endstop -
+  it is used during homing operations.
+
+Common commands
+===============
+
+This section lists some commonly used run-time commands. It is likely
+only of interest to developers looking to gain insight into Klippy.
+
+* schedule_digital_out oid=%c clock=%u value=%c : This command will
+  schedule a change to a digital output GPIO pin at the given clock
+  time. To use this command a 'config_digital_out' command with the
+  same 'oid' parameter must have been issued during firmware
+  configuration.
+
+* schedule_pwm_out oid=%c clock=%u value=%c : Schedules a change to a
+  hardware PWM output pin. See the 'schedule_digital_out' and
+  'config_pwm_out' commands for more info.
+
+* schedule_soft_pwm_out oid=%c clock=%u value=%c : Schedules a change
+  to a software PWM output pin. See the 'schedule_digital_out' and
+  'config_soft_pwm_out' commands for more info.
+
+* query_analog_in oid=%c clock=%u sample_ticks=%u sample_count=%c
+  rest_ticks=%u min_value=%hu max_value=%hu : This command sets up a
+  recurring schedule of analog input samples. To use this command a
+  'config_analog_in' command with the same 'oid' parameter must have
+  been issued during firmware configuration. The samples will start as
+  of 'clock' time, it will report on the obtained value every
+  'rest_ticks' clock ticks, it will over-sample 'sample_count' number
+  of times, and it will pause 'sample_ticks' number of clock ticks
+  between over-sample samples. The 'min_value' and 'max_value'
+  parameters implement a safety feature - the firmware will verify the
+  sampled value (after any oversampling) is always between the
+  supplied range. This is intended for use with pins attached to
+  thermistors controlling heaters - it can be used to check that a
+  heater is within a temperature range.
+
+* get_status : This command causes the firmware to generate a "status"
+  response message. The host sends this command once a second to
+  obtain the value of the micro-controller clock and to estimate the
+  drift between host and micro-controller clocks. It enables the host
+  to accurately estimate the micro-controller clock.
+
+Stepper commands
+----------------
+
+* queue_step oid=%c interval=%u count=%hu add=%hi : This command
+  schedules 'count' number of steps for the given stepper, with
+  'interval' number of clock ticks between each step. The first step
+  will be 'interval' number of clock ticks since the last scheduled
+  step for the given stepper. If 'add' is non-zero then the interval
+  will be adjusted by 'add' amount after each step. This command
+  appends the given interval/count/add sequence to a per-stepper
+  queue. There may be hundreds of these sequences queued during normal
+  operation. New sequence are appended to the end of the queue and as
+  each sequence completes its 'count' number of steps it is popped
+  from the front of the queue. There may be tens of thousands of steps
+  queued in the firmware and every step will have a reliable and
+  predictable schedule time.
+
+* set_next_step_dir oid=%c dir=%c : This command specifies the value
+  of the dir_pin that the next queue_step command will use.
+
+* reset_step_clock oid=%c clock=%u : Normally, step timing is relative
+  to the last step for a given stepper. This command resets the clock
+  so that the next step is relative to the supplied 'clock' time. The
+  host usually only sends this command at the start of a print or
+  after a long idle period for the stepper (for example a Z stepper
+  move after printing an extensive layer).
+
+* end_stop_home oid=%c clock=%u rest_ticks=%u pin_value=%c : This
+  command is used during stepper "homing" operations. To use this
+  command a 'config_end_stop' command with the same 'oid' parameter
+  must have been issued during firmware configuration. When invoked,
+  the firmware will sample the endstop pin every 'rest_ticks' clock
+  ticks and check if it has a value equal to 'pin_value'. If the value
+  matches then the movement queue for the associated stepper will be
+  cleared and the stepper will come to an immediate halt. The host
+  uses this command to implement homing - the host instructs the
+  endstop to sample for the endstop trigger and then it issues a
+  series of queue_step commands to the stepper to move it towards the
+  endstop. Once the stepper hits the endstop, the trigger will be
+  detected, the movement halted, and the host notified.
diff --git a/docs/Overview.md b/docs/Overview.md
index ba230117..6c7a9458 100644
--- a/docs/Overview.md
+++ b/docs/Overview.md
@@ -5,7 +5,9 @@ See [code overview](Code_Overview.md) for developer information on the
 structure and layout of the Klipper code.
 
 See [protocol](Protocol.md) for developer information on the messaging
-protocol between host and firmware.
+protocol between host and firmware. See also
+[firmware commands](Firmware_Commands.md) for a high-level description
+of some commands implemented in the firmware.
 
 See [debugging](Debugging.md) for developer information on how to test
 and debug Klipper.