94 lines
4.2 KiB
Markdown
94 lines
4.2 KiB
Markdown
This document describes the overall code layout and major code flow of
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Klipper.
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Directory Layout
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================
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The **src/** directory contains the C source for the micro-controller
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code. The **src/avr/** directory contains specific code for Atmel
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ATmega micro-controllers. The **src/simulator/** contains code stubs
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that allow the micro-controller to be test compiled on other
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architectures.
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The **klippy/** directory contains the C and Python source for the
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host part of the firmware.
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The **config/** directory contains example printer configuration
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files.
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The **scripts/** directory contains build-time scripts useful for
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compiling the micro-controller code.
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During compilation, the build may create an **out/** directory. This
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contains temporary build time objects. The final micro-controller
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object that is built is in **out/klipper.elf.hex**
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Micro-controller code flow
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==========================
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Execution of the micro-controller code starts in **src/avr/main.c**
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which calls sched_main() located in **src/sched.c**. The sched_main()
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code starts by running all functions that have been tagged with the
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DECL_INIT() macro. It then goes on to repeatedly run all functions
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tagged with the DECL_TASK() macro.
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One of the main task functions is command_task() located in
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**src/command.c**. This function processes incoming serial commands
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and runs the associated command function for them. Command functions
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are declared using the DECL_COMMAND() macro.
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Task, init, and command functions always run with interrupts enabled
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(however, they can temporarily disable interrupts if needed). These
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functions should never pause, delay, or do any work that lasts more
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than a few micro-seconds. These functions schedule work at specific
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times by scheduling timers.
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Timer functions are scheduled by calling sched_timer() (located in
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**src/sched.c**). The scheduler code will arrange for the given
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function to be called at the requested clock time. Timer interrupts
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are initially handled in an interrupt handler in **src/avr/timer.c**,
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but this just calls sched_timer_kick() located in **src/sched.c**. The
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timer interrupt leads to execution of schedule timer functions. Timer
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functions always run with interrupts disabled. The timer functions
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should always complete within a few micro-seconds. At completion of
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the timer event, the function may choose to reschedule itself.
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In the event an error is detected the code can invoke shutdown() (a
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macro which calls sched_shutdown() located in **src/sched.c**).
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Invoking shutdown() causes all functions tagged with the
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DECL_SHUTDOWN() macro to be run. Shutdown functions always run with
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interrupts disabled.
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Much of the functionality of the micro-controller involves working
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with General-Purpose Input/Output pins (GPIO). In order to abstract
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the low-level architecture specific code from the high-level task
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code, all GPIO events are implemented via wrappers. These wrappers are
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located in **src/avr/gpio.c**. The code is compiled with gcc's "-flto
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-fwhole-program" optimization which does an excellent job of inlining
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functions across compilation units, so most of these tiny gpio
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functions are inlined into their callers, and there is no run-time
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cost to using them.
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Klippy code overview
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====================
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The host code (Klippy) is intended to run on a low-cost computer (such
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as a Raspberry Pi) paired with the micro-controller. The code is
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primarily written in Python, however it does use CFFI to implement
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some functionality in C code.
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Initial execution starts in **klippy/klippy.py**. This reads the
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command-line arguments, opens the printer config file, instantiates
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the main printer objects, and starts the serial connection. The main
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execution of gcode commands is in the process_commands() method in
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**klippy/gcode.py**. This code translates the gcode commands into
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printer object calls, which frequently translate the actions to
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commands to be executed on the micro-controller (as declared via the
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DECL_COMMAND macro in the micro-controller code).
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There are three threads in the Klippy host code. The main thread
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handles incoming gcode commands. A second thread (which resides
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entirely in the **klippy/serialqueue.c** C code) handles low-level IO
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with the serial port. The third thread is used to process response
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messages from the micro-controller in the Python code.
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