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AVR port: Add instructions for changing the CPU in use. Add details on location of functions on ATmega2560/2561.

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Kelvin Lawson
2010-02-21 19:29:57 +00:00
parent a09d1d7376
commit 611bf65ea5
1 changed files with 34 additions and 1 deletions
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35
ports/avr/README
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@@ -145,7 +145,9 @@ minutes, so be patient.
The test application also toggles a bit on PORTB once per second if the
test was successful. On the STK500 this can be connected to the LEDs for
a visual indication of a passed test without the UART.
a visual indication of a passed test without the UART. If you do not wish to
use the UART you may use this to indicate passed tests, a UART is not
a requirement for running the tests.
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
@@ -167,6 +169,24 @@ functions. You can generally simply replace the call to the test modules by
a call to your own application startup code.
---------------------------------------------------------------------------
PORTING TO OTHER HARDWARE PLATFORMS
If you are using a CPU other than the ATmega16, change the PART definition
in the Makefile to your own CPU.
On CPUs with multiple UARTs, the port uses UART0 to output debug
information. If you wish to use an alternative UART you may change the
registers in uart.c. Note that a UART is not vital for Atomthreads
operation anyway, it is only used by the test applications for indicating
test pass/fail status. If you do not wish to use a UART you may instead
flash a LED or use some other indication mechanism.
The Atomthreads port uses Timer 1 to drive the system tick. If you wish
to use some other timer then you may do so by modifying atomport.c.
---------------------------------------------------------------------------
RAM FOOTPRINT & STACK USAGE
@@ -255,3 +275,16 @@ test applications. You may choose whatever layout you like.
---------------------------------------------------------------------------
HANDLING CPUS WITH LARGE PROGRAM SPACES
Some devices such as the ATmega2560/2561 support program memory larger than
128KB. GCC defines __AVR_3_BYTE_PC__ for such devices, which is detected in
the architecture port wherever special handling is required. GCC does not
at this time support function pointers greater than 16-bits, however, which
means that the thread_shell() routine which is the entry point for all
threads must be located in the bottom 128KB of program space. You may need
to force this using a linker directive.
---------------------------------------------------------------------------