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docs: Add a section with micro-controller porting tips to Code_Overview.md

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Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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Kevin O'Connor
2018-07-11 14:35:28 -04:00
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@@ -334,6 +334,59 @@ Useful steps:
to micro-controller commands. This is useful to exercise corner
cases and to check for regressions.
Porting to a new micro-controller
=================================
This section provides some tips on porting Klipper's micro-controller
code to a new architecture. This type of activity requires good
knowledge of embedded development and hands-on access to the target
micro-controller.
Useful steps:
1. Start by identifying any 3rd party libraries that will be used
during the port. Common examples include "CMSIS" wrappers and
manufacturer "HAL" libraries. All 3rd party code needs to be GNU
GPLv3 compatible. The 3rd party code should be committed to the
Klipper lib/ directory. Update the lib/README file with information
on where and when the library was obtained. It is preferable to
copy the code into the Klipper repository unchanged, but if any
changes are required then those changes should be listed explicitly
in the lib/README file.
2. Create a new architecture sub-directory in the src/ directory and
add initial Kconfig and Makefile support. Use the existing
architectures as a guide. The src/simulator provides a basic
example of a minimum starting point.
3. The first main coding task is to bring up communication support to
the target board. This is the most difficult step in a new port.
Once basic communication is working, the remaining steps tend to be
much easier. It is typical to use an RS-232 style serial port
during initial development as these types of hardware devices are
generally easier to enable and control. During this phase, make
liberal use of helper code from the src/generic/ directory (check
how src/simulator/Makefile includes the generic C code into the
build). It is also necessary to define timer_read_time() (which
returns the current system clock) in this phase, but it is not
necessary to fully support timer irq handling.
4. Get familiar with the the console.py tool (as described in the
[debugging document](Debugging.md)) and verify connectivity to the
micro-controller with it. This tool translates the low-level
micro-controller communication protocol to a human readable form.
5. Add support for timer dispatch from hardware interrupts. See
Klipper
[commit 970831ee](https://github.com/KevinOConnor/klipper/commit/970831ee0d3b91897196e92270d98b2a3067427f)
as an example of steps 1-5 done for the LPC176x architecture.
6. Bring up basic GPIO input and output support. See Klipper
[commit c78b9076](https://github.com/KevinOConnor/klipper/commit/c78b90767f19c9e8510c3155b89fb7ad64ca3c54)
as an example of this.
7. Bring up additional peripherals - for example see Klipper commit
[65613aed](https://github.com/KevinOConnor/klipper/commit/65613aeddfb9ef86905cb1dade9e773a02ef3c27),
[c812a40a](https://github.com/KevinOConnor/klipper/commit/c812a40a3782415e454b04bf7bd2158a6f0ec8b5),
and
[c381d03a](https://github.com/KevinOConnor/klipper/commit/c381d03aad5c3ee761169b7c7bced519cc14da29).
8. Create a sample Klipper config file in the config/ directory. Test
the micro-controller with the main klippy.py program.
9. Consider adding build test cases in the test/ directory.
Time
====