I am dealing with a new microcontroller LPC4088 from NXP. I needed 2 weeks to study and write a working examples for peripherals: IOCONFIG, GPIO, TIMERS, PWM and ADC. Please take a look at my repositories here. This is how you will get a feeling for how I work and what my skill level is.
Until now I could simply disable interrupts and work without them. Now I want to deal with UART peripheral device which needs interrupts. I have never programmed interupts but know something about ARM interrupts. Sadly just in theory. Currently I am studying these two documents:
- LPC4088 user guide (NVIC p.80 & UART1 p.461),
- Cortex-M4 devices generic user manual
It became clear to me that I need to study ARM Cortex-M4 microprocessor besides the LPC4088 microcontroller which I got the hang of somehow. I know that I should put ARM exception vectors at the beginning of the program - usually in the startup code. But I don't know how to do this because what I got with the microcontroller is already compiled startup code (object file) which presumably defines exception vectors, reset handler which sets stacks for C and then jumps to function main() in C source code written by user.
After compilation of my programs using GCC ARM compiler I allways get this prompt, which must allso be the clue which I don't understand because of my inexperience with ARM mcpu's directly:
*****
***** You must modify vector checksum value in *.bin and *.hex files.
*****
I was thinking of reverse ingeneering the startup code using the Segger Jlink and fixing the exception vectors there, but there must be any other way besides writing my own open source startup code... So do you have any suggestions or examples which would be even better for me.
ADD: I really looked hard and got no source code for the startup code. This is what I got:
The only way to somehow manipulate vectors therefore must be hidden inside the linker script, which is the only part that is still a source code and it looks like this:
/* Linker script for mbed LPC1768 */
/* Linker script to configure memory regions. */
MEMORY
{
FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 512K
RAM (rwx) : ORIGIN = 0x100000E8, LENGTH = (64K - 0xE8)
USB_RAM(rwx) : ORIGIN = 0x20000000, LENGTH = 16K
ETH_RAM(rwx) : ORIGIN = 0x20004000, LENGTH = 16K
}
/* Linker script to place sections and symbol values. Should be used together
* with other linker script that defines memory regions FLASH and RAM.
* It references following symbols, which must be defined in code:
* Reset_Handler : Entry of reset handler
*
* It defines following symbols, which code can use without definition:
* __exidx_start
* __exidx_end
* __etext
* __data_start__
* __preinit_array_start
* __preinit_array_end
* __init_array_start
* __init_array_end
* __fini_array_start
* __fini_array_end
* __data_end__
* __bss_start__
* __bss_end__
* __end__
* end
* __HeapLimit
* __StackLimit
* __StackTop
* __stack
*/
ENTRY(Reset_Handler)
SECTIONS
{
.text :
{
KEEP(*(.isr_vector))
*(.text*)
KEEP(*(.init))
KEEP(*(.fini))
/* .ctors */
*crtbegin.o(.ctors)
*crtbegin?.o(.ctors)
*(EXCLUDE_FILE(*crtend?.o *crtend.o) .ctors)
*(SORT(.ctors.*))
*(.ctors)
/* .dtors */
*crtbegin.o(.dtors)
*crtbegin?.o(.dtors)
*(EXCLUDE_FILE(*crtend?.o *crtend.o) .dtors)
*(SORT(.dtors.*))
*(.dtors)
*(.rodata*)
KEEP(*(.eh_frame*))
} > FLASH
.ARM.extab :
{
*(.ARM.extab* .gnu.linkonce.armextab.*)
} > FLASH
__exidx_start = .;
.ARM.exidx :
{
*(.ARM.exidx* .gnu.linkonce.armexidx.*)
} > FLASH
__exidx_end = .;
__etext = .;
.data : AT (__etext)
{
__data_start__ = .;
Image$$RW_IRAM1$$Base = .;
*(vtable)
*(.data*)
. = ALIGN(4);
/* preinit data */
PROVIDE (__preinit_array_start = .);
KEEP(*(.preinit_array))
PROVIDE (__preinit_array_end = .);
. = ALIGN(4);
/* init data */
PROVIDE (__init_array_start = .);
KEEP(*(SORT(.init_array.*)))
KEEP(*(.init_array))
PROVIDE (__init_array_end = .);
. = ALIGN(4);
/* finit data */
PROVIDE (__fini_array_start = .);
KEEP(*(SORT(.fini_array.*)))
KEEP(*(.fini_array))
PROVIDE (__fini_array_end = .);
. = ALIGN(4);
/* All data end */
__data_end__ = .;
} > RAM
.bss :
{
__bss_start__ = .;
*(.bss*)
*(COMMON)
__bss_end__ = .;
Image$$RW_IRAM1$$ZI$$Limit = . ;
} > RAM
.heap :
{
__end__ = .;
end = __end__;
*(.heap*)
__HeapLimit = .;
} > RAM
/* .stack_dummy section doesn't contains any symbols. It is only
* used for linker to calculate size of stack sections, and assign
* values to stack symbols later */
.stack_dummy :
{
*(.stack)
} > RAM
/* Set stack top to end of RAM, and stack limit move down by
* size of stack_dummy section */
__StackTop = ORIGIN(RAM) + LENGTH(RAM);
__StackLimit = __StackTop - SIZEOF(.stack_dummy);
PROVIDE(__stack = __StackTop);
/* Check if data + heap + stack exceeds RAM limit */
ASSERT(__StackLimit >= __HeapLimit, "region RAM overflowed with stack")
/* Code can explicitly ask for data to be
placed in these higher RAM banks where
they will be left uninitialized.
*/
.AHBSRAM0 (NOLOAD):
{
Image$$RW_IRAM2$$Base = . ;
*(AHBSRAM0)
Image$$RW_IRAM2$$ZI$$Limit = .;
} > USB_RAM
.AHBSRAM1 (NOLOAD):
{
Image$$RW_IRAM3$$Base = . ;
*(AHBSRAM1)
Image$$RW_IRAM3$$ZI$$Limit = .;
} > ETH_RAM
}
There is allso a makefile which looks like this and is contributing the prompt that I get at the end of every compilation:
# This file was automagically generated by mbed.org. For more information,
# see http://mbed.org/handbook/Exporting-to-GCC-ARM-Embedded
GCC_BIN =
PROJECT = executaable
OBJECTS = ./main.o
SYS_OBJECTS = ./mbed/TARGET_LPC4088/TOOLCHAIN_GCC_ARM/startup_LPC408x.o ./mbed/TARGET_LPC4088/TOOLCHAIN_GCC_ARM/retarget.o ./mbed/TARGET_LPC4088/TOOLCHAIN_GCC_ARM/system_LPC407x_8x_177x_8x.o ./mbed/TARGET_LPC4088/TOOLCHAIN_GCC_ARM/board.o ./mbed/TARGET_LPC4088/TOOLCHAIN_GCC_ARM/cmsis_nvic.o
INCLUDE_PATHS = -I. -I./mbed -I./mbed/TARGET_LPC4088 -I./mbed/TARGET_LPC4088/TOOLCHAIN_GCC_ARM -I./mbed/TARGET_LPC4088/TARGET_NXP -I./mbed/TARGET_LPC4088/TARGET_NXP/TARGET_LPC408X -I./mbed/TARGET_LPC4088/TARGET_NXP/TARGET_LPC408X/TARGET_LPC4088
LIBRARY_PATHS = -L./mbed/TARGET_LPC4088/TOOLCHAIN_GCC_ARM
LIBRARIES = -lmbed
LINKER_SCRIPT = ./mbed/TARGET_LPC4088/TOOLCHAIN_GCC_ARM/LPC4088.ld
###############################################################################
AS = $(GCC_BIN)arm-none-eabi-as
CC = $(GCC_BIN)arm-none-eabi-gcc
CPP = $(GCC_BIN)arm-none-eabi-g++
LD = $(GCC_BIN)arm-none-eabi-gcc
OBJCOPY = $(GCC_BIN)arm-none-eabi-objcopy
OBJDUMP = $(GCC_BIN)arm-none-eabi-objdump
SIZE = $(GCC_BIN)arm-none-eabi-size
CPU = -mcpu=cortex-m4 -mthumb -mfpu=fpv4-sp-d16 -mfloat-abi=softfp
CC_FLAGS = $(CPU) -c -g -fno-common -fmessage-length=0 -Wall -fno-exceptions -ffunction-sections -fdata-sections -fomit-frame-pointer
CC_FLAGS += -MMD -MP
CC_SYMBOLS = -DTARGET_LPC4088 -DTARGET_M4 -DTARGET_CORTEX_M -DTARGET_NXP -DTARGET_LPC408X -DTOOLCHAIN_GCC_ARM -DTOOLCHAIN_GCC -D__CORTEX_M4 -DARM_MATH_CM4 -D__FPU_PRESENT=1 -DMBED_BUILD_TIMESTAMP=1429428454.91 -D__MBED__=1
LD_FLAGS = $(CPU) -Wl,--gc-sections --specs=nano.specs -u _printf_float -u _scanf_float -Wl,--wrap,main
LD_FLAGS += -Wl,-Map=$(PROJECT).map,--cref
LD_SYS_LIBS = -lstdc++ -lsupc++ -lm -lc -lgcc -lnosys
ifeq ($(DEBUG), 1)
CC_FLAGS += -DDEBUG -O0
else
CC_FLAGS += -DNDEBUG -Os
endif
all: $(PROJECT).bin $(PROJECT).hex
clean:
rm -f $(PROJECT).bin $(PROJECT).elf $(PROJECT).hex $(PROJECT).map $(PROJECT).lst $(OBJECTS) $(DEPS)
.s.o:
$(AS) $(CPU) -o $@ $<
.c.o:
$(CC) $(CC_FLAGS) $(CC_SYMBOLS) -std=gnu99 $(INCLUDE_PATHS) -o $@ $<
.cpp.o:
$(CPP) $(CC_FLAGS) $(CC_SYMBOLS) -std=gnu++98 -fno-rtti $(INCLUDE_PATHS) -o $@ $<
$(PROJECT).elf: $(OBJECTS) $(SYS_OBJECTS)
$(LD) $(LD_FLAGS) -T$(LINKER_SCRIPT) $(LIBRARY_PATHS) -o $@ $^ $(LIBRARIES) $(LD_SYS_LIBS) $(LIBRARIES) $(LD_SYS_LIBS)
@echo ""
@echo "*****"
@echo "***** You must modify vector checksum value in *.bin and *.hex files."
@echo "*****"
@echo ""
$(SIZE) $@
$(PROJECT).bin: $(PROJECT).elf
@$(OBJCOPY) -O binary $< $@
$(PROJECT).hex: $(PROJECT).elf
@$(OBJCOPY) -O ihex $< $@
$(PROJECT).lst: $(PROJECT).elf
@$(OBJDUMP) -Sdh $< > $@
lst: $(PROJECT).lst
size:
$(SIZE) $(PROJECT).elf
DEPS = $(OBJECTS:.o=.d) $(SYS_OBJECTS:.o=.d)
-include $(DEPS)
