AVR uses Hardward architecture with separate address space for program
memory (flash) and data memory (RAM). Normal program flow can only
access data memory which means that all variables - including const
variables - have to be copied into RAM to be accessible. (This happens
automatically during startup.)
It is possible to work around this limitation in software but that
can have severe impact on performance and/or API complexity. It is hardly
feasible to change NuttX interfaces in a way that would allow to make use
of this workaround.
On newer AVR families, there is an alternative option enabled by this patch.
These chips map part of their program memory (a 32kB window) into data
memory address space. This patch leverages this feature and adds support
for placing const variables into the mapped window. No copy to RAM is done
for them.
Const variables are therefore loaded directly from flash (not consuming
RAM) while still being available to be used by any NuttX interface.
Linker script of breadxavr board is changed to make use of these changes.
Tested by verifying string addresses - parameters in printf call
in a custom application (and also by running the application and verifying
its output.)
Documentation tested by build.
Signed-off-by: Kerogit <kr.git@kerogit.eu>
This patch adds a document that describes why const variables need to be
copied into the RAM in AVR architecture for normal program flow in NuttX.
It then describes options of accessing them directly from the flash without
need to do any copying.
Patch was tested by building the documentation.
Signed-off-by: Kerogit <kr.git@kerogit.eu>
Migrated teensy 2.0 README.txt to RST format. Moved common tool-chain
information to the chip page and provided back-link.
Signed-off-by: Matteo Golin <matteo.golin@gmail.com>
The document context-switch-notes.rst was leaking into "Supported Platforms"
table of contents. To fix this, it was moved to separate common directory
and referenced from AVR index.rst
Similar to that, the gpio_intr_mux.rst document was leaking into list
of supported AVR families. This too was fixed by moving it to separate
docs directory.
The change was tested by building the Documentation using make html
Signed-off-by: Kerogit <kr.git@kerogit.eu>
After a mailing list suggestion, the indirection that enabled
ARCH_TOOLCHAIN_GCC only when user requested it is removed.
The indirection was a safety measure for chips and boards with linker
scripts that (possibly) do not handle keeping for example .vectors
section even if the linker considers it unreferenced.
Instead, all existing configurations now disable
CONFIG_DEBUG_OPT_UNUSED_SECTIONS to prevent the linker from removing
any code. (Preserving previous behaviour.) This can be removed again
at some point after making sure that corresponding linker script
only removes code that is truly unused.
Signed-off-by: Kerogit <kr.git@kerogit.eu>
This patch adds additional information to breadxavr board for AVR DA family
development. The text now covers how to use Button input driver and also
adds some information about using the hardware.
Signed-off-by: Kerogit <kr.git@kerogit.eu>
Unlike the Hello, world example, the NSH configuration can serve
as a starting point for testing other examples.
Signed-off-by: Kerogit <kr.git@kerogit.eu>
This patch adds definitions for listed chips. No other changes are needed
as the chips are similar to the previously supported AVR128DA28 and all
that is needed is some definitions for extra peripherals.
AVR DA/DB family chips have single interrupt vector for all changes
on an I/O port. This poses problem when multiple drivers want to claim
the same interrupt (might happen for example with button and discrete
joystick drivers using pins on the same port.)
The I/O multiplexer solves it by providing interface similar
to irq_attach. However, it allows registration of multiple handlers
for the same interrupt vector with additional information recording
which pins should be serviced by each handler.
Only handler for pins that triggered the interrupt is then called.
Initial support adds chip specific files like Kconfig, flags for the compiler,
and basic functionality like system timer. Some files are stubs derived
from corresponding ATmega files but without the functionality they are
supposed to add (to be done in later patches)
Part of the work is altered copies of corresponding files for ATMega MCUs.
Initially supported is AVR128DA28.
- migrated /README are removed from /boards
- there are a lot of READMEs that should be further converted to rst.
At the moment they are moved to Documentation/platforms and included in rst files
