atomthreads/ports/stm8/README-COSMIC

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Library:      Atomthreads
Author:       Kelvin Lawson <info@atomthreads.com>
Website:      http://atomthreads.com
License:      BSD Revised

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STM8 PORT - COSMIC COMPILER

This folder contains a port of the Atomthreads real time kernel for the
STM8 processor architecture. These instructions cover usage of Atomthreads
with the Cosmic compiler (CXSTM8).

Compiler-agnostic aspects of the usage of Atomthreads can be found in README.

Instructions for users of the other compilers are available in README-SDCC,
README-IAR and README-RAISONANCE.


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PREREQUISITES

The port works out-of-the-box with the Cosmic compiler tools for building.
Applications are generated in .s19 form and can be programmed with any
supporting programming software, including the free STVP (visual
programmer tool). At this time there does not appear to be a command-line
programmer application suitable for use with STM8.

The Cosmic compiler and STVP are currently Windows-only applications. For
users of other operating systems the Cosmic compiler may work in 
environments like Wine, but the USB programming tools are less likely to
be supported. Both the compiler and the USB programming tool for
STM8S-Discovery (STVP) can, however, be run successfully within a VM such
as VirtualBox.

The core software prerequisites are therefore:
 * Cosmic STM8 compiler
 * Programming software (e.g. ST's STVP tool)

Optionally, application build, program and debug can be carried out
using ST's visual debug tool, STVD.

Use with alternative compiler tools may require some modification, but you
can easily replace STVP by your own favourite programmer if required.


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MEMORY MODEL

The sample build configurations use the Cosmic modsl0 memory model. This
places all data outside of the short 0x0-0x255 page0 area, which allows
large data blocks such as thread stacks to fit. You could instead use the
more efficient mods0 memory model which places data in the short page0
area, and force large data areas like thread stacks outside of page0 by
adding @near modifiers or specifying data areas by the linker file etc.

The default configuration is modsl0 (place outside of page0) to allow for
the most portable application compilation, with the option of optimising
this by placing data in page0 if desired. There is no requirement that you
compile your applications using the modsl0 memory model.


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BUILDING THE SOURCE

You may build Atomthreads using whichever build environment you desire. For
your convenience we provide both a ready-rolled Makefile-based build system
and an STVD visual debugger project. The STVD project permits easy
building, programming and debugging, but does not easily support building
a wide range of application builds within the same project, which is
useful for building the numerous automated tests. For the automated tests
you may find it easier to use the Makefile which automatically builds all
automated tests.


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BUILD VIA STVD PROJECT

For building applications using STVD you can use the sample workspace
atomthreads-sample-stvd.stw which contains both Cosmic compiler and
Raisonance compiler based projects. You can also import the Cosmic-only
project file atomthreads-sample-cosmic.stp directly. This builds a sample
full application which runs the "sem1" automated test. Applications can be
downloaded directly to the target hardware (e.g. STM8S-Discovery) and run
via the integrated debugger. Press the exclamation button to run, and
confirm that the LED flashes once per second (if running on an
STM8S-Discovery) to ensure that the test has passed. 

This is also a good starting point for building your own applications:
simply modify the file tests-main.c which starts the test application.
You can run any of the other automated tests by replacing the file sem1.c
within the project by another of the tests within the atomthreads tests
folder. This is rather painful using a GUI interface due to the large
number of test files, and you may prefer to use the Makefile-based system
instead which builds all automated tests in one command.


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BUILD VIA MAKEFILE

A Makefile is also provided for building the kernel, port and automated
tests. This is particularly useful for building the automated tests
because many different independent applications need to be built which is
not easily achieved within the STVD environment.

For a Windows system you can obtain a Make application suitable for use
with the Cosmic compiler from:

 * http://www.cosmic-software.com/comp_utils/GNU_Make.zip

Assuming you install the above into C:\Program Files\GNU_MAKE, you
should set up your environment variables as follows:

 * set PATH=%PATH%;C:\Program Files\GNU_MAKE;C:\Program Files\COSMIC\CXSTM8_16K
 * set MAKE_MODE=DOS


The full build is carried out using simply:

 * make -f cosmic.mak

All objects are built into the 'build-cosmic' folder under ports/stm8. The
build process builds separate target applications for each automated test,
and appropriate .stm8 or .s19 files can be found in the build folder ready
for downloading to and running on the target. Because of the limited
resources on the STM8, and the large amount of automated tests, each test
is built and run as a separate application.


All built objects etc can be cleaned using:

 * make -f cosmic.mak clean


The Atomthreads sources are documented using Doxygen markup. You can build
both the kernel and STM8 port documentation from this folder using:

 * make -f cosmic.mak doxygen


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PROGRAMMING MAKEFILE-BUILT APPLICATIONS TO THE TARGET DEVICE

When developing within STVD, programs can be downloaded directly to the
target. If, however, you are building applications separately using a
Makefile or similar, then you are not able to program the application
using STVD. None of the tools delivered by ST appear to be designed to
cater for those who build applications externally, but it is possible using
STVP.

The following development workflow can be used (note that these settings
apply to the STM8S-Discovery):

 * Build app using Makefile.
 * Open STVP and configure to use Swim ST-Link for CPU STM8105C6.
 * Open application .s19 file and program using "Program All Tabs".

Unfortunately STVP does not have a command to reset and start the CPU
running, but it can be forced into doing so by reconfiguring the
programmer:

 * Select "Configure ST Visual Programmer" from the Configure menu.

Your application should now be programmed and running.

If you wish to program and run another application then you can open and
program it in STVP, then use the Configure menu again to reset the
device and start it running.

Other programming tools may exist but are not apparent in the toolset
delivered for use the STM8S Discovery platform.

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RUNNING THE AUTOMATED TESTS

Atomthreads contains a set of generic kernel tests which can be run on any
port to prove that all core functionality is working on your target.

The full set of tests can be found in the top-level 'tests' folder. The
Makefile builds each of these tests as independent applications in the
'build' folder. Run them individually using the STVP process described
above. For example to run the 'kern1.c' test use STVP to program and run
it.

You may also build the tests using the STVD project, but to run each
different test you must manually remove the previous test module (e.g.
kern1.c) and replace it with one of other tests, which can be quite time
consuming compared to building all tests in one command via the Makefile.

To view the test results, watch the LED on the STM8S-Discovery. This will
flash once per second if the test passed, and once every 1/8 second if the
test failed.

If you wish to use the UART, connect a serial debug cable to your target
platform (defaults to 9600bps 8N1). On starting, the test applications
print out "Go" on the UART. Once the test is complete they will print
out "Pass" or "Fail", along with other information if the test failed.

Most of the tests complete within a few seconds, but some (particularly
the stress tests) can take several seconds, so be patient. 

The full suite of tests endeavours to exercise as much of the kernel code
as possible, and can be used for quick confirmation of core OS
functionality if you ever need to make a change to the kernel or port.

The test application main() is contained in tests-main.c. This initialises
the OS, creates a main thread, and calls out to the test modules. It also
initialises the UART driver for use by stdout.


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WRITING APPLICATIONS

The easiest way to start a new application which utilises the Atomthreads
scheduler is to base your main application startup on tests-main.c. This
initialises the OS, sets up a UART and calls out to the test module entry
functions. You can generally simply replace the call to the test modules by
a call to your own application startup code.

Projects developed within STVD can be started using the sample project
atomthreads-sample-cosmic.stp. If you wish to create your own STVD project
from scratch, then you should ensure you change the project settings for
both Debug and Release builds as follows:

* Toolset: "STM8 Cosmic"
* MCU Selection: Appropriate for your platform (STM8S10C56 for Discovery)
* C Compiler Memory Model: "+modsl0"
* C Compiler Preprocessor Definitions: CPU part (e.g. "STM8S105")
* C Compiler Preprocessor Definitions: Enable thread stack checking if
  desired by adding "ATOM_STACK_CHECKING", for example the full
  preprocessor line for Discovery might be: "STM8S105 ATOM_STACK_CHECKING"
* Linker Input: Zero Page from 0x2 to 0xFF (allows NULL-pointer checks by
  preventing the linker from using address 0x0.
* Linker Input: Ram from 0x100 to 0x7BF (if you wish to allow 0x100 to
  0x7BF for application usage, and 0x7C0 to 0x7FF for startup stack.


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COSMIC COMPILER VIRTUAL REGISTERS

The STM8 has only very few CPU registers, so the Cosmic compiler augments
them with three "virtual" registers, which are simply locations in fast
memory. These registers are called c_x, c_y and c_lreg.

The Atomthreads context switch for Cosmic/STM8 takes advantage of the fact
that all CPU and virtual registers are automatically saved on the stack by
the compiler when calling out to C functions (and even then only if
necessary).

For cooperative context switches (where a thread calls an OS kernel
function to schedule itself out), any of these registers which should be
preserved across the function call are automatically saved on the stack by
the compiler before the context switch is even called. This means that no
CPU or virtual registers actually have to be saved in the context switch
routine, making cooperative switches potentially very cheap if few
registers must be preserved.

For preemptive switches (where an ISR has interrupted a thread and wishes
to switch to a new thread), the interrupt handler prologue automatically
saves all CPU registers (actually done automatically by the CPU) and all
of the virtual registers. In this case all registers must always be saved
because the ISR has no knowledge of what registers the interrupted thread
was using, so we cannot take advantage of the potential for saving fewer
than the full set of registers that we achieve with cooperative switches.
With the Cosmic compiler, interrupt handlers that call out to C functions
(as would happen on a thread switch) always save the CPU registers (done by
the CPU in fact) and the virtual registers c_x and c_y. For the Atomthreads
port we force interrupt handlers to also save the virtual register c_lreg.
This is to ensure that the interrupted thread's c_lreg value is preserved
across a thread switch, but also ensures that longs can be used within the
OS kernel code called by interrupt handlers (c_lreg is used by the compiler
for handling longs and floats).

An alternative scheme would be to not save c_lreg in all interrupt
handlers and instead save it in the context-switch function. This would
allow interrupt handlers to avoid saving the 4-byte c_lreg on the stack,
but it would mean that any OS kernel code called by interrupt handlers
could not deal with longs, which would be an unfortunate burden on the
core portable OS code just for the benefit of this one architecture and
compiler. It would also mean that c_lreg is always saved unnecessarily
for every cooperative context switch. 


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