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STM8: Add README for IAR EWSTM8 compiler.

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Kelvin Lawson
2010-06-01 22:40:54 +01:00
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52
ports/stm8/README
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@@ -7,10 +7,11 @@ License: BSD Revised
---------------------------------------------------------------------------
STM8 PORT
STM8 PORT - COSMIC COMPILER
This folder contains a port of the Atomthreads real time kernel for the
STM8 processor architecture.
STM8 processor architecture. These instructions cover usage of Atomthreads
with the Cosmic compiler (CXSTM8).
All of the cross-platform kernel code is contained in the top-level
'kernel' folder, while ports to specific CPU architectures are contained in
@@ -43,10 +44,12 @@ provides an easy mechanism for building, downloading and running the test
suite to prove the OS on your target.
The port was carried out and tested on an STM8S105C6 running within an
STM8S-Discovery board, utilising the Cosmic compiler tools. It is possible
to use it with other processors in the STM8 range, as well as other
hardware platforms and compilers, with minimal changes. Platform and
compiler specific code has been kept to an absolute minimum.
STM8S-Discovery board, and supports both the Cosmic and IAR compiler tools.
It is possible to use it with other processors in the STM8 range, as well
as other hardware platforms and compilers, with minimal changes. Platform
and compiler specific code has been kept to an absolute minimum. This
README covers usage of Atomthreads with the Cosmic compiler. Instructions
for users of the IAR compiler are available in README-IAR.
---------------------------------------------------------------------------
@@ -73,7 +76,7 @@ The core software prerequisites are therefore:
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
Use with alternative compiler tools will require some modification, but you
can easily replace STVP by your own favourite programmer if required.
@@ -255,10 +258,11 @@ 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. Each of
these tests is built as an independent application 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.
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.
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
@@ -347,9 +351,9 @@ what level of stack the application code in question requires.
At this time the maximum stack consumed by the test threads within the
automated test modules is 95 bytes of stack, and the main test thread has
been seen to consume 161 bytes of stack. At this time the timer2 test is
the largest consumer of test thread stack (95 bytes) and the sem4 test
consumes the largest main thread stack (161 bytes). If your applications
been seen to consume 163 bytes of stack. At this time the timer2 test is
the largest consumer of test thread stack (95 bytes) and the sem3 test
consumes the largest main thread stack (163 bytes). If your applications
have large amounts of local data or call several subroutines then you may
find that you need larger than 128 bytes.
@@ -468,7 +472,8 @@ 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.
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
@@ -479,18 +484,19 @@ 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 also saves all
CPU and virtual registers. In this case all registers must always be saved
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 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
(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

372
ports/stm8/README-IAR Normal file
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@@ -0,0 +1,372 @@
---------------------------------------------------------------------------
Library: Atomthreads
Author: Kelvin Lawson <kelvinl@users.sf.net>
Website: http://atomthreads.com
License: BSD Revised
---------------------------------------------------------------------------
STM8 PORT - IAR 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 IAR Embedded Workbench compiler (EWSTM8).
All of the cross-platform kernel code is contained in the top-level
'kernel' folder, while ports to specific CPU architectures are contained in
the 'ports' folder tree. A port to a CPU architecture can comprise just one
or two modules which provide the architecture-specific functionality, such
as the context-switch routine which saves and restores processor registers
on a thread switch. In this case, the kernel port is split into two files:
* atomport.c: Those functions which can be written in C
* atomport-asm-iar.s: The main register save/restore assembler routines
Each Atomthreads port requires also a header file which describes various
architecture-specific details such as appropriate types for 8-bit, 16-bit
etc variables, the port's system tick frequency, and macros for performing
interrupt lockouts / critical sections:
* atomuser.h: Port-specific header required by the kernel for each port
A few additional source files are also included here:
* tests-main.c: Main application file (used for launching automated tests)
* uart.c: UART wrapper to allow use of stdio/printf()
* stm8s-periphs/*.*: Peripheral drivers as delivered by ST (no changes
to distributed code).
Atomthreads includes a suite of automated tests which prove the key OS
functionality, and can be used with any architecture ports. This port
provides an easy mechanism for building, downloading and running the test
suite to prove the OS on your target.
The port was carried out and tested on an STM8S105C6 running within an
STM8S-Discovery board, and supports both the Cosmic and IAR compiler tools.
It is possible to use it with other processors in the STM8 range, as well
as other hardware platforms and compilers, with minimal changes. Platform
and compiler specific code has been kept to an absolute minimum. This
README covers usage of Atomthreads with the IAR compiler. Instructions for
users of the Cosmic compiler are available in README-COSMIC.
---------------------------------------------------------------------------
PREREQUISITES
The port works out-of-the-box with the IAR compiler tools for building.
Applications are generated in .out form and can be programmed and debugged
using the IAR Embedded Workbench GUI.
IAR Embedded Workbench for STM8 is a Windows-only application. For
users of other operating systems the IAR tools may work in environments
like Wine, but the USB programming tools are less likely to be supported.
Embedded Workbench for STM8 can, however, be run successfully within a VM
such as VirtualBox, including USB download and debug.
The core software prerequisites are therefore:
* IAR Embedded Workbench STM8
Use with alternative compiler tools will require some modification, but you
can easily replace the EWSTM8 IDE by your own favourite programmer if
required.
---------------------------------------------------------------------------
BUILDING THE SOURCE
A sample EWSTM8 project has been provided. This permits easy building,
programming and debugging within the EWSTM8 IDE.
Unlike the Cosmic compiler port, there is currently no Makefile-based build
provided for use with EWSTM8. Only a sample IDE project is available.
---------------------------------------------------------------------------
BUILD VIA EWSTM8 PROJECT
For building applications using the EWSTM8 IDE you can use the sample
project file atomthreads-sample-iar.ewp. 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. You can start the application running, 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. In time a Makefile will be provided that will build all of the
automated tests with one command. Currently the Makefile supports only the
Cosmic compiler.
---------------------------------------------------------------------------
BUILD VIA MAKEFILE
The STM8 port Makefile currently only supports building for the Cosmic
compiler. An IAR-capable Makefile will be released soon.
---------------------------------------------------------------------------
STM8S-DISCOVERY SPECIFICS
There are very minimal board-specific aspects to the STM8 port so it is
trivial to run Atomthreads on other STM8 platforms.
The test applications make use of a LED to indicate test pass/fail status.
This is currently configured to use a bit in GPIOD, which on the Discovery
board maps to the board's only LED. You may change the port and register
bit in tests-main.c to utilise a different pin on other hardware platforms.
You may also completely omit the LED flashing in the test application if
you prefer to use the UART for monitoring test status.
The test applications also make use of the UART to print out pass/fail
indications and other information. For this you should connect a serial
cable to the Discovery board via the external pin connectors. Use of
a UART is not required if you prefer to use the LED or some other method
of notifying test pass/fail status.
To connect a serial cable to the Discovery you will need to connect to
the following pins on the external connectors:
Vcc: CN2 pin 8
GND: CN2 pin 7
UART TX: CN4 pin 10 (connect to RX at the PC end)
UART RX: CN4 pin 9 (connect to TX at the PC end)
Note that the board uses TTL levels so you may need to use a level
converter. External level converters may need to be powered using
a Vdd of 5v, which can be achieved by positioning JP1 on the Discovery.
The STM8 device on the Discovery only offers UART2. If you are using a
different device or wish to use an alternative UART then you must change
the stm8s_conf.h file.
If you are using a CPU other than the STM8S105C6 you should modify
the project C/C++ Compiler Preprocessor settings for both Debug and Release
projects to specify your CPU (currently set to STM8S105), and set the
target device in the project "General Options". You may also wish to enable
any CPU peripherals which you wish to use in the stm8s_conf.h file.
---------------------------------------------------------------------------
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. Each
test is built and run as a single individual application. To run the full
test suite with EWSTM8 you must modify the EWSTM8 sample project many
times, swapping out the 'sem1' test included by default. This is not
currently automated, so for the time being you must swap the test module,
build the project and run it, repeating this for each test. For example to
run the 'kern1.c' test you remove 'sem1.c' from the project and add
'kern1.c', then build the project and run on the target.
A Makefile to build all applications in one command is planned, but for
the time being a Makefile is only available for the Cosmic compiler.
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.
---------------------------------------------------------------------------
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 EWSTM8 can be started using the sample project
atomthreads-sample-iar.ewp. If you wish to create your own EWSTM8 project
from scratch, then you should ensure you change the project settings for
both Debug and Release builds as follows:
* General Options -> Target -> Device: CPU part (e.g. "STM8S105C6")
* C/C++ Compiler -> Diagnostics: Suppress "Pa050"
* C/C++ Compiler -> Preprocessor -> Defined Symbols:
CPU part (e.g. "STM8S105")
Thread stack-checking if required ("ATOM_STACK_CHECKING")
For example "STM8S105, ATOM_STACK_CHECKING"
* Assembler -> Diagnostics: Suppress "Pa050"
* Repeat above for Debug and Release projects (you may want to
disable ATOM_STACK_CHECKING for Release builds).
Other options you may wish to change:
* Tools -> Options -> Editor -> EOL Characters: "Preserve". This preserves
the line endings, bearing in mind that the Atomthreads kernels works
with many host operating system toolchains.
* Options -> Debugger -> "ST Link" (e.g. for STM8S Discovery)
Add the .C and .S modules from the following folders:
* kernel
* ports/stm8
* ports/stm8s-periphs
Set include paths as appropriate.
---------------------------------------------------------------------------
RAM FOOTPRINT & STACK USAGE
The Atomthreads kernel is written in well-structured pure C which is highly
portable and not targeted at any particular compiler or CPU architecture.
For this reason it is not highly optimised for the STM8 architecture, and
by its nature will likely have a higher text and data footprint than an
RTOS targeted at the STM8 architecture only. The emphasis here is on
C-based portable, readable and maintainable code which can run on any CPU
architecture, from the 8-bitters up.
A good rule of thumb when using Atomthreads on the STM8 architecture is
that a minimum of 1KB RAM is required in order to support an application
with 4 or 5 threads and the idle thread. If a minimum of approximately
128 bytes per thread stack is acceptable then you will benefit from the
easy-to-read, portable implementation of an RTOS herein.
The major consumer of RAM when using Atomthreads is your thread stacks.
Functionality that is shared between several kernel modules is farmed out
to separate functions, resulting in readable and maintainable code but
with some associated stack cost of calling out to subroutines. Further,
each thread stack is used for saving its own registers on a context
switch, and there is no separate interrupt stack which means that each
thread stack has to be able to cope with the maximum stack usage of the
kernel (and application) interrupt handlers.
Clearly the stack requirement for each thread depends on what your
application code does, and what memory model is used etc, but generally
you should find that 128 bytes is enough to allow for the thread to be
switched out (and thus save its registers) while deep within a kernel
or application call stack, and similarly enough to provide stack for
interrupt handlers interrupting while the thread is deep within a kernel
or application call stack. You will need to increase this depending on
what level of stack the application code in question requires.
At this time the maximum stack consumed by the test threads within the
automated test modules is 85 bytes of stack, and the main test thread has
been seen to consume 193 bytes of stack. At this time the queue9 test is
the largest consumer of test thread stack (85 bytes) and the sem8 test
consumes the largest main thread stack (193 bytes). If your applications
have large amounts of local data or call several subroutines then you may
find that you need larger than 128 bytes.
You may monitor the stack usage of your application threads during runtime
by defining the macro ATOM_STACK_CHECKING and calling
atomThreadStackCheck(). This macro is defined by default in the EWSTM8
Debug project so that the automated test modules can check for stack
overflows, but you may wish to undefine this in your application
when you are happy that the stack usage is acceptable. Enabling
ATOM_STACK_CHECKING will increase the size of your threads' TCBs
slightly, and will incur a minor CPU cycles overhead whenever threads are
created due to prefilling the thread stack with a known value.
With careful consideration and few threads it would be possible to use
a platform with 512 bytes RAM, but not all of the automated test suite
would run on such a platform (some of the test modules use 6 threads: a
main thread together with 4 test threads and the idle thread).
---------------------------------------------------------------------------
INTERRUPT HANDLING
Interrupt handlers use the stack of the thread which was running when the
interrupt occurred. If no thread rescheduling occurs during the ISR then
on exit from the ISR any data stacked by the ISR on the thread's stack is
popped off the stack and execution of the thread resumes. If a reschedule
during the ISR causes a context switch to a new thread, then the ISR's
data will remain on the thread's stack until the thread is scheduled back
in.
Interrupt priorities (via the ITC_SPRx registers) are left in their
default power-on state, which disables interrupt nesting. Kernel changes
may be required to support interrupt nesting.
Note that the STM8 programming manual currently describes the following
feature:
"Fast interrupt handling through alternate register files (up to 4
contexts) with standard stack compatible mode (for real time OS
kernels)"
This feature was implemented by ST in the core but has to date never been
included in any STM8 products. If it is included in future products then
you will need to put the device in the stack compatible mode described.
---------------------------------------------------------------------------
WRITING NEW INTERRUPT HANDLERS
All interrupt handlers which will call out to the OS kernel and potentially
cause a thread switch must call atomIntEnter() and atomIntExit(). An
example of this can be seen in the timer tick ISR in atomport.c.
You may also implement fast interrupt handlers in the system which do not
call atomIntEnter()/atomIntExit(), however these ISRs cannot perform OS
functions such as posting semaphores or effecting a thread switch.
---------------------------------------------------------------------------
IAR COMPILER VIRTUAL REGISTERS
The STM8 has only very few CPU registers, so the IAR compiler augments
them with sixteen "virtual" registers, which are simply locations in fast
memory. These registers are called ?b0 to ?b15.
The Atomthreads context switch for IAR/STM8 takes advantage of the fact
that all CPU and most virtual registers are automatically saved on the
stack by the compiler when calling out to C functions (and even then only
if necessary). Only the virtual registers ?b8 to ?b15 are expected to be
preserved by called functions, so these are the only registers that
callers to the context switch routine will not automatically save if
necessary.
For cooperative context switches (where a thread calls an OS kernel
function to schedule itself out), most registers will therefore already
be saved on a thread's stack if necessary. Only ?b8 to ?b15 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 the
virtual registers ?b0 to ?b7. Still only the registers ?b8 to ?b15 have to
be saved by the context-switch routine, but in this case ?b0 to ?b7 and the
CPU registers are always saved on the thread's stack by the ISR prologue.
This is 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.
---------------------------------------------------------------------------