| demo_project(3avr) | avr-libc | demo_project(3avr) |
NAME¶
demo_project - A simple project
SYNOPSIS¶
Detailed Description¶
At this point, you should have the GNU tools configured, built, and installed on your system. In this chapter, we present a simple example of using the GNU tools in an AVR project. After reading this chapter, you should have a better feel as to how the tools are used and how a Makefile can be configured.
The Project¶
This project will use the pulse-width modulator (PWM) to ramp an LED on and off every two seconds. An AT90S2313 processor will be used as the controller. The circuit for this demonstration is shown in the schematic diagram. If you have a development kit, you should be able to use it, rather than build the circuit, for this project.
Note
The source code is given in demo.c. For the sake of this example, create a file called demo.c containing this source code. Some of the more important parts of the code are:
Note [1]:
- OCR the name of the OCR register used to control the PWM (usually either OCR1 or OCR1A)
- DDROC the name of the DDR (data direction register) for the OC output
- OC1 the pin number of the OC1[A] output within its port
- TIMER1_TOP the TOP value of the timer used for the PWM (1023 for 10-bit PWMs, 255 for devices that can only handle an 8-bit PWM)
- TIMER1_PWM_INIT the initialization bits to be set into control register 1A in order to setup 10-bit (or 8-bit) phase and frequency correct PWM mode
- TIMER1_CLOCKSOURCE the clock bits to set in the respective control register to start the PWM timer; usually the timer runs at full CPU clock for 10-bit PWMs, while it runs on a prescaled clock for 8-bit PWMs
Note [2]:
Note [3]:
Note [4]:
Note [5]:
Note [6]:
Note [7]:
Note [8]:
The Source Code¶
/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* <joerg@FreeBSD.ORG> wrote this file. As long as you retain this notice you
* can do whatever you want with this stuff. If we meet some day, and you think
* this stuff is worth it, you can buy me a beer in return. Joerg Wunsch
* ----------------------------------------------------------------------------
*
* Simple AVR demonstration. Controls a LED that can be directly
* connected from OC1/OC1A to GND. The brightness of the LED is
* controlled with the PWM. After each period of the PWM, the PWM
* value is either incremented or decremented, that's all.
*
* $Id$
*/ #include <inttypes.h> #include <avr/io.h> #include <avr/interrupt.h> #include <avr/sleep.h> #include "iocompat.h" /* Note [1] */ enum { UP, DOWN }; ISR (TIMER1_OVF_vect) /* Note [2] */ {
static uint16_t pwm; /* Note [3] */
static uint8_t direction;
switch (direction) /* Note [4] */
{
case UP:
if (++pwm == TIMER1_TOP)
direction = DOWN;
break;
case DOWN:
if (--pwm == 0)
direction = UP;
break;
}
OCR = pwm; /* Note [5] */ } void ioinit (void) /* Note [6] */ {
/* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */
TCCR1A = TIMER1_PWM_INIT;
/*
* Start timer 1.
*
* NB: TCCR1A and TCCR1B could actually be the same register, so
* take care to not clobber it.
*/
TCCR1B |= TIMER1_CLOCKSOURCE;
/*
* Run any device-dependent timer 1 setup hook if present.
*/ #if defined(TIMER1_SETUP_HOOK)
TIMER1_SETUP_HOOK(); #endif
/* Set PWM value to 0. */
OCR = 0;
/* Enable OC1 as output. */
DDROC = _BV (OC1);
/* Enable timer 1 overflow interrupt. */
TIMSK = _BV (TOIE1);
sei (); } int main (void) {
ioinit ();
/* loop forever, the interrupts are doing the rest */
for (;;) /* Note [7] */
sleep_mode();
return (0); }
Compiling and Linking¶
This first thing that needs to be done is compile the source. When compiling, the compiler needs to know the processor type so the -mmcu option is specified. The -Os option will tell the compiler to optimize the code for efficient space usage (at the possible expense of code execution speed). The -g is used to embed debug info. The debug info is useful for disassemblies and doesn't end up in the .hex files, so I usually specify it. Finally, the -c tells the compiler to compile and stop -- don't link. This demo is small enough that we could compile and link in one step. However, real-world projects will have several modules and will typically need to break up the building of the project into several compiles and one link.
$ avr-gcc -g -Os -mmcu=atmega8 -c demo.c
The compilation will create a demo.o file. Next we link it into a binary called demo.elf.
$ avr-gcc -g -mmcu=atmega8 -o demo.elf demo.o
It is important to specify the MCU type when linking. The compiler uses the -mmcu option to choose start-up files and run-time libraries that get linked together. If this option isn't specified, the compiler defaults to the 8515 processor environment, which is most certainly what you didn't want.
Examining the Object File¶
Now we have a binary file. Can we do anything useful with it (besides put it into the processor?) The GNU Binutils suite is made up of many useful tools for manipulating object files that get generated. One tool is avr-objdump, which takes information from the object file and displays it in many useful ways. Typing the command by itself will cause it to list out its options.
For instance, to get a feel of the application's size, the -h option can be used. The output of this option shows how much space is used in each of the sections (the .stab and .stabstr sections hold the debugging information and won't make it into the ROM file).
An even more useful option is -S. This option disassembles the binary file and intersperses the source code in the output! This method is much better, in my opinion, than using the -S with the compiler because this listing includes routines from the libraries and the vector table contents. Also, all the 'fix-ups' have been satisfied. In other words, the listing generated by this option reflects the actual code that the processor will run.
$ avr-objdump -h -S demo.elf > demo.lst
Here's the output as saved in the demo.lst file:
demo.elf: file format elf32-avr Sections: Idx Name Size VMA LMA File off Algn
0 .text 000000be 00000000 00000000 00000094 2**1
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .data 00000000 00800060 000000be 00000152 2**0
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000003 00800060 00800060 00000152 2**0
ALLOC
3 .stab 0000066c 00000000 00000000 00000154 2**2
CONTENTS, READONLY, DEBUGGING
4 .stabstr 00000d95 00000000 00000000 000007c0 2**0
CONTENTS, READONLY, DEBUGGING
5 .comment 00000011 00000000 00000000 00001555 2**0
CONTENTS, READONLY Disassembly of section .text: 00000000 <__ctors_end>:
0: 20 e0 ldi r18, 0x00 ; 0
2: a0 e6 ldi r26, 0x60 ; 96
4: b0 e0 ldi r27, 0x00 ; 0
6: 01 c0 rjmp .+2 ; 0xa <.do_clear_bss_start> 00000008 <.do_clear_bss_loop>:
8: 1d 92 st X+, r1 0000000a <.do_clear_bss_start>:
a: a3 36 cpi r26, 0x63 ; 99
c: b2 07 cpc r27, r18
e: e1 f7 brne .-8 ; 0x8 <.do_clear_bss_loop> 00000010 <__vector_8>: #include "iocompat.h" /* Note [1] */ enum { UP, DOWN }; ISR (TIMER1_OVF_vect) /* Note [2] */ {
10: 1f 92 push r1
12: 0f 92 push r0
14: 0f b6 in r0, 0x3f ; 63
16: 0f 92 push r0
18: 11 24 eor r1, r1
1a: 2f 93 push r18
1c: 8f 93 push r24
1e: 9f 93 push r25
20: 80 91 60 00 lds r24, 0x0060 ; 0x800060 <__DATA_REGION_ORIGIN__>
24: 90 91 61 00 lds r25, 0x0061 ; 0x800061 <__DATA_REGION_ORIGIN__+0x1>
static uint16_t pwm; /* Note [3] */
static uint8_t direction;
switch (direction) /* Note [4] */
28: 20 91 62 00 lds r18, 0x0062 ; 0x800062 <direction.1505>
2c: 22 23 and r18, r18
2e: a9 f0 breq .+42 ; 0x5a <__SREG__+0x1b>
30: 21 30 cpi r18, 0x01 ; 1
32: 49 f4 brne .+18 ; 0x46 <__SREG__+0x7>
if (++pwm == TIMER1_TOP)
direction = DOWN;
break;
case DOWN:
if (--pwm == 0)
34: 01 97 sbiw r24, 0x01 ; 1
36: 90 93 61 00 sts 0x0061, r25 ; 0x800061 <__DATA_REGION_ORIGIN__+0x1>
3a: 80 93 60 00 sts 0x0060, r24 ; 0x800060 <__DATA_REGION_ORIGIN__>
3e: 00 97 sbiw r24, 0x00 ; 0
40: 11 f4 brne .+4 ; 0x46 <__SREG__+0x7>
direction = UP;
42: 10 92 62 00 sts 0x0062, r1 ; 0x800062 <direction.1505>
break;
}
OCR = pwm; /* Note [5] */
46: 9b bd out 0x2b, r25 ; 43
48: 8a bd out 0x2a, r24 ; 42 }
4a: 9f 91 pop r25
4c: 8f 91 pop r24
4e: 2f 91 pop r18
50: 0f 90 pop r0
52: 0f be out 0x3f, r0 ; 63
54: 0f 90 pop r0
56: 1f 90 pop r1
58: 18 95 reti
static uint8_t direction;
switch (direction) /* Note [4] */
{
case UP:
if (++pwm == TIMER1_TOP)
5a: 01 96 adiw r24, 0x01 ; 1
5c: 90 93 61 00 sts 0x0061, r25 ; 0x800061 <__DATA_REGION_ORIGIN__+0x1>
60: 80 93 60 00 sts 0x0060, r24 ; 0x800060 <__DATA_REGION_ORIGIN__>
64: 8f 3f cpi r24, 0xFF ; 255
66: 23 e0 ldi r18, 0x03 ; 3
68: 92 07 cpc r25, r18
6a: 69 f7 brne .-38 ; 0x46 <__SREG__+0x7>
direction = DOWN;
6c: 21 e0 ldi r18, 0x01 ; 1
6e: 20 93 62 00 sts 0x0062, r18 ; 0x800062 <direction.1505>
72: e9 cf rjmp .-46 ; 0x46 <__SREG__+0x7> 00000074 <ioinit>: void ioinit (void) /* Note [6] */ {
/* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */
TCCR1A = TIMER1_PWM_INIT;
74: 83 e8 ldi r24, 0x83 ; 131
76: 8f bd out 0x2f, r24 ; 47
* Start timer 1.
*
* NB: TCCR1A and TCCR1B could actually be the same register, so
* take care to not clobber it.
*/
TCCR1B |= TIMER1_CLOCKSOURCE;
78: 8e b5 in r24, 0x2e ; 46
7a: 81 60 ori r24, 0x01 ; 1
7c: 8e bd out 0x2e, r24 ; 46 #if defined(TIMER1_SETUP_HOOK)
TIMER1_SETUP_HOOK(); #endif
/* Set PWM value to 0. */
OCR = 0;
7e: 1b bc out 0x2b, r1 ; 43
80: 1a bc out 0x2a, r1 ; 42
/* Enable OC1 as output. */
DDROC = _BV (OC1);
82: 82 e0 ldi r24, 0x02 ; 2
84: 87 bb out 0x17, r24 ; 23
/* Enable timer 1 overflow interrupt. */
TIMSK = _BV (TOIE1);
86: 84 e0 ldi r24, 0x04 ; 4
88: 89 bf out 0x39, r24 ; 57
sei ();
8a: 78 94 sei }
8c: 08 95 ret 0000008e <main>: void ioinit (void) /* Note [6] */ {
/* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */
TCCR1A = TIMER1_PWM_INIT;
8e: 83 e8 ldi r24, 0x83 ; 131
90: 8f bd out 0x2f, r24 ; 47
* Start timer 1.
*
* NB: TCCR1A and TCCR1B could actually be the same register, so
* take care to not clobber it.
*/
TCCR1B |= TIMER1_CLOCKSOURCE;
92: 8e b5 in r24, 0x2e ; 46
94: 81 60 ori r24, 0x01 ; 1
96: 8e bd out 0x2e, r24 ; 46 #if defined(TIMER1_SETUP_HOOK)
TIMER1_SETUP_HOOK(); #endif
/* Set PWM value to 0. */
OCR = 0;
98: 1b bc out 0x2b, r1 ; 43
9a: 1a bc out 0x2a, r1 ; 42
/* Enable OC1 as output. */
DDROC = _BV (OC1);
9c: 82 e0 ldi r24, 0x02 ; 2
9e: 87 bb out 0x17, r24 ; 23
/* Enable timer 1 overflow interrupt. */
TIMSK = _BV (TOIE1);
a0: 84 e0 ldi r24, 0x04 ; 4
a2: 89 bf out 0x39, r24 ; 57
sei ();
a4: 78 94 sei
ioinit ();
/* loop forever, the interrupts are doing the rest */
for (;;) /* Note [7] */
sleep_mode();
a6: 85 b7 in r24, 0x35 ; 53
a8: 80 68 ori r24, 0x80 ; 128
aa: 85 bf out 0x35, r24 ; 53
ac: 88 95 sleep
ae: 85 b7 in r24, 0x35 ; 53
b0: 8f 77 andi r24, 0x7F ; 127
b2: 85 bf out 0x35, r24 ; 53
b4: f8 cf rjmp .-16 ; 0xa6 <main+0x18> 000000b6 <exit>:
b6: f8 94 cli
b8: 00 c0 rjmp .+0 ; 0xba <_exit> 000000ba <_exit>:
ba: f8 94 cli 000000bc <__stop_program>:
bc: ff cf rjmp .-2 ; 0xbc <__stop_program>
Linker Map Files¶
avr-objdump is very useful, but sometimes it's necessary to see information about the link that can only be generated by the linker. A map file contains this information. A map file is useful for monitoring the sizes of your code and data. It also shows where modules are loaded and which modules were loaded from libraries. It is yet another view of your application. To get a map file, I usually add -Wl,-Map,demo.map to my link command. Relink the application using the following command to generate demo.map (a portion of which is shown below).
$ avr-gcc -g -mmcu=atmega8 -Wl,-Map,demo.map -o demo.elf demo.o
Some points of interest in the demo.map file are:
.rela.plt
*(.rela.plt) .text 0x0000000000000000 0xbe
*(.vectors)
*(.vectors)
*(.progmem.gcc*)
0x0000000000000000 . = ALIGN (0x2)
0x0000000000000000 __trampolines_start = .
*(.trampolines)
.trampolines 0x0000000000000000 0x0 linker stubs
*(.trampolines*)
0x0000000000000000 __trampolines_end = .
*libprintf_flt.a:*(.progmem.data)
*libc.a:*(.progmem.data)
*(.progmem*)
0x0000000000000000 . = ALIGN (0x2)
*(.jumptables)
*(.jumptables*)
*(.lowtext)
*(.lowtext*)
0x0000000000000000 __ctors_start = .
The .text segment (where program instructions are stored) starts at
location 0x0.
*(.fini2)
*(.fini2)
*(.fini1)
*(.fini1)
*(.fini0)
.fini0 0x00000000000000ba 0x4 /usr/lib/gcc/avr/7.3.0/avr4/libgcc.a(_exit.o)
*(.fini0)
0x00000000000000be _etext = . .data 0x0000000000800060 0x0 load address 0x00000000000000be
[!provide] PROVIDE (__data_start, .)
*(.data)
.data 0x0000000000800060 0x0 demo.o
.data 0x0000000000800060 0x0 /build/reproducible-path/avr-libc-2.0.0+Atmel3.7.0/libc/avr-libc/avr/lib/avr4/exit.o
.data 0x0000000000800060 0x0 /usr/lib/gcc/avr/7.3.0/avr4/libgcc.a(_exit.o)
.data 0x0000000000800060 0x0 /usr/lib/gcc/avr/7.3.0/avr4/libgcc.a(_clear_bss.o)
*(.data*)
*(.gnu.linkonce.d*)
*(.rodata)
*(.rodata*)
*(.gnu.linkonce.r*)
0x0000000000800060 . = ALIGN (0x2)
0x0000000000800060 _edata = .
[!provide] PROVIDE (__data_end, .) .bss 0x0000000000800060 0x3
0x0000000000800060 PROVIDE (__bss_start, .)
*(.bss)
.bss 0x0000000000800060 0x3 demo.o
.bss 0x0000000000800063 0x0 /build/reproducible-path/avr-libc-2.0.0+Atmel3.7.0/libc/avr-libc/avr/lib/avr4/exit.o
.bss 0x0000000000800063 0x0 /usr/lib/gcc/avr/7.3.0/avr4/libgcc.a(_exit.o)
.bss 0x0000000000800063 0x0 /usr/lib/gcc/avr/7.3.0/avr4/libgcc.a(_clear_bss.o)
*(.bss*)
*(COMMON)
0x0000000000800063 PROVIDE (__bss_end, .)
0x00000000000000be __data_load_start = LOADADDR (.data)
0x00000000000000be __data_load_end = (__data_load_start + SIZEOF (.data)) .noinit 0x0000000000800063 0x0
[!provide] PROVIDE (__noinit_start, .)
*(.noinit*)
[!provide] PROVIDE (__noinit_end, .)
0x0000000000800063 _end = .
[!provide] PROVIDE (__heap_start, .) .eeprom 0x0000000000810000 0x0
*(.eeprom*)
0x0000000000810000 __eeprom_end = .
The last address in the .text segment is location 0x114 ( denoted by
_etext ), so the instructions use up 276 bytes of FLASH.
The .data segment (where initialized static variables are stored) starts at location 0x60, which is the first address after the register bank on an ATmega8 processor.
The next available address in the .data segment is also location 0x60, so the application has no initialized data.
The .bss segment (where uninitialized data is stored) starts at location 0x60.
The next available address in the .bss segment is location 0x63, so the application uses 3 bytes of uninitialized data.
The .eeprom segment (where EEPROM variables are stored) starts at location 0x0.
The next available address in the .eeprom segment is also location 0x0, so there aren't any EEPROM variables.
Generating Intel Hex Files¶
We have a binary of the application, but how do we get it into the processor? Most (if not all) programmers will not accept a GNU executable as an input file, so we need to do a little more processing. The next step is to extract portions of the binary and save the information into .hex files. The GNU utility that does this is called avr-objcopy.
The ROM contents can be pulled from our project's binary and put into the file demo.hex using the following command:
$ avr-objcopy -j .text -j .data -O ihex demo.elf demo.hex
The resulting demo.hex file contains:
:1000000020E0A0E6B0E001C01D92A336B207E1F700 :100010001F920F920FB60F9211242F938F939F93DD :100020008091600090916100209162002223A9F0EC :10003000213049F40197909361008093600000970C :1000400011F4109262009BBD8ABD9F918F912F91F8 :100050000F900FBE0F901F9018950196909361001E :10006000809360008F3F23E0920769F721E020939F :100070006200E9CF83E88FBD8EB581608EBD1BBC69 :100080001ABC82E087BB84E089BF7894089583E836 :100090008FBD8EB581608EBD1BBC1ABC82E087BB54 :1000A00084E089BF789485B7806885BF889585B7D7 :0E00B0008F7785BFF8CFF89400C0F894FFCF8B :00000001FF
The -j option indicates that we want the information from the .text and .data segment extracted. If we specify the EEPROM segment, we can generate a .hex file that can be used to program the EEPROM:
$ avr-objcopy -j .eeprom --change-section-lma .eeprom=0 -O ihex demo.elf demo_eeprom.hex
There is no demo_eeprom.hex file written, as that file would be empty.
Starting with version 2.17 of the GNU binutils, the avr-objcopy command that used to generate the empty EEPROM files now aborts because of the empty input section .eeprom, so these empty files are not generated. It also signals an error to the Makefile which will be caught there, and makes it print a message about the empty file not being generated.
Letting Make Build the Project¶
Rather than type these commands over and over, they can all be placed in a make file. To build the demo project using make, save the following in a file called Makefile.
Note
PRG = demo OBJ = demo.o #MCU_TARGET = at90s2313 #MCU_TARGET = at90s2333 #MCU_TARGET = at90s4414 #MCU_TARGET = at90s4433 #MCU_TARGET = at90s4434 #MCU_TARGET = at90s8515 #MCU_TARGET = at90s8535 #MCU_TARGET = atmega128 #MCU_TARGET = atmega1280 #MCU_TARGET = atmega1281 #MCU_TARGET = atmega1284p #MCU_TARGET = atmega16 #MCU_TARGET = atmega163 #MCU_TARGET = atmega164p #MCU_TARGET = atmega165 #MCU_TARGET = atmega165p #MCU_TARGET = atmega168 #MCU_TARGET = atmega169 #MCU_TARGET = atmega169p #MCU_TARGET = atmega2560 #MCU_TARGET = atmega2561 #MCU_TARGET = atmega32 #MCU_TARGET = atmega324p #MCU_TARGET = atmega325 #MCU_TARGET = atmega3250 #MCU_TARGET = atmega329 #MCU_TARGET = atmega3290 #MCU_TARGET = atmega32u4 #MCU_TARGET = atmega48 #MCU_TARGET = atmega64 #MCU_TARGET = atmega640 #MCU_TARGET = atmega644 #MCU_TARGET = atmega644p #MCU_TARGET = atmega645 #MCU_TARGET = atmega6450 #MCU_TARGET = atmega649 #MCU_TARGET = atmega6490 MCU_TARGET = atmega8 #MCU_TARGET = atmega8515 #MCU_TARGET = atmega8535 #MCU_TARGET = atmega88 #MCU_TARGET = attiny2313 #MCU_TARGET = attiny24 #MCU_TARGET = attiny25 #MCU_TARGET = attiny26 #MCU_TARGET = attiny261 #MCU_TARGET = attiny44 #MCU_TARGET = attiny45 #MCU_TARGET = attiny461 #MCU_TARGET = attiny84 #MCU_TARGET = attiny85 #MCU_TARGET = attiny861 OPTIMIZE = -O2 DEFS = LIBS = # You should not have to change anything below here. CC = avr-gcc # Override is only needed by avr-lib build system. override CFLAGS = -g -Wall $(OPTIMIZE) -mmcu=$(MCU_TARGET) $(DEFS) override LDFLAGS = -Wl,-Map,$(PRG).map OBJCOPY = avr-objcopy OBJDUMP = avr-objdump all: $(PRG).elf lst text eeprom $(PRG).elf: $(OBJ)
$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LIBS) # dependency: demo.o: demo.c iocompat.h clean:
rm -rf *.o $(PRG).elf *.eps *.png *.pdf *.bak
rm -rf *.lst *.map $(EXTRA_CLEAN_FILES) lst: $(PRG).lst %.lst: %.elf
$(OBJDUMP) -h -S $< > $@ # Rules for building the .text rom images text: hex bin srec hex: $(PRG).hex bin: $(PRG).bin srec: $(PRG).srec %.hex: %.elf
$(OBJCOPY) -j .text -j .data -O ihex $< $@ %.srec: %.elf
$(OBJCOPY) -j .text -j .data -O srec $< $@ %.bin: %.elf
$(OBJCOPY) -j .text -j .data -O binary $< $@ # Rules for building the .eeprom rom images eeprom: ehex ebin esrec ehex: $(PRG)_eeprom.hex ebin: $(PRG)_eeprom.bin esrec: $(PRG)_eeprom.srec %_eeprom.hex: %.elf
$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O ihex $< $@ \
|| { echo empty $@ not generated; exit 0; } %_eeprom.srec: %.elf
$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O srec $< $@ \
|| { echo empty $@ not generated; exit 0; } %_eeprom.bin: %.elf
$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O binary $< $@ \
|| { echo empty $@ not generated; exit 0; } # Every thing below here is used by avr-libc's build system and can be ignored # by the casual user. FIG2DEV = fig2dev EXTRA_CLEAN_FILES = *.hex *.bin *.srec dox: eps png pdf eps: $(PRG).eps png: $(PRG).png pdf: $(PRG).pdf %.eps: %.fig
$(FIG2DEV) -L eps $< $@ %.pdf: %.fig
$(FIG2DEV) -L pdf $< $@ %.png: %.fig
$(FIG2DEV) -L png $< $@
Reference to the source code¶
Author¶
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| Fri Nov 24 2023 23:59:10 | Version 2.0.0 |