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6.8 An embeddable application with interrupt handling

This section describes how to convert the application in A semihosted application with interrupt handling into an

embeddable application. Converting the application requires additional files:

vectors.s

This file contains exception vectors and exception handlers. For this example ROM is fixed at

0x0.

init.s

This file performs ROM/RAM remapping (if required), initializes stack pointers and interrupts for

each mode, and branches to __main in the C library. The C library code at __main eventually

calls main().

ROM/RAM remapping is not used in this example. A sample scatter-load description for

remapping is available in install_directory\Examples\embedded\rps_irq.

retarget.c

This file implements a retarget layer for low-level I/O. Typically, this would contain your own

target-dependent implementations. This example provides implementations of fputc(),

ferror(), _sys_exit(), _ttywrch() and __user_initial_stackheap().

The #define USE_SERIAL_PORT selects code to output characters from the serial port of an

ARM Development (PID) Board.

serial.c

This file implements a simple polled RS232 serial driver for the ARM Integrator board. It outputs

single characters on Serial Port A at 9600 Baud, 8 bit, no parity, 1 stop bit.

The file uart.c instantiates the uart0 structure. The scatter-loading files place this structure

over the peripheral registers. See Using scatter loading with memory-mapped I/O for details on

defining I/O structures.

heap.s

This file exports the symbol bottom_of_heap.

stack.s

This file exports the symbol top_of_stacks.

To ensure that no semihosting SWI-using function is linked in from the C library, #pragma

import(__use_no_semihosting_swi) is referenced from main().

6.8.1 Memory map

The scatter-load descriptor file defines one load region, FLASH, and five execution regions:

FLASH

The entire program is placed in ROM. The RO code executes from FLASH. The execution

address of FLASH is the same as its load address (0x24000000), so it does not have to be

moved.

32bitRAM

The exception vector table vectors.s must appear in RAM at 0x0, so the +First command

is used to place it first in the image. The RW data is relocated from FLASH to 32bitRAM above

the vector code at 0x0. The ZI data is initialized in RAM above the RW data.

ROM/RAM remapping is not used in this example. A sample scatter-load description for

remapping is available in install_directory\Examples\Embedded\rps_irq.

HEAP

The heap is located at the end of memory used by the variables. The object heap.o contains a

symbol that is used to setup the heap base.

STACKS

The top of stack at 0x40000. The object stack.o contains a symbol that is used to set up the

stack top.

UART0

Memory-mapped I/O at 0x16000000. The object uart.o contains symbols that are used to

reserve the memory-mapped I/O. This memory is not zero-initialized.

6.8.2 Building the example

To build the example, use the build_c.bat batch file, the CodeWarrior IDE project file rps_irq.mcp with a target

of EmbedScatter, or a makefile containing the following (the indented lines are a continuation of the single line

above):

armasm -g vectors.s

armasm -g -PD "ROM_RAM_REMAP SETL {TRUE}" init.s

armasm -g stack.s

armasm -g heap.s

REM Use the following lines to build without using the serial port.

armcc -c -g -O1 main.c -I..\include -DEMBEDDED -DROM_RAM_REMAP

armcc -c -g -O1 retarget.c

REM Use the following lines to build using the serial port.

REM armcc -c -g -O1 main.c -I..\include -DEMBEDDED -DROM_RAM_REMAP

Writing Code for ROM