demo_project(3)
👑 demo_project — straight out of the avr-libc manual 👑
bestie. sit down. hydrate. we're doing the classic demo project and it's gonna be adorable and educational at the same time 💖
✨ NAME ✨
demo_project — yeah that's the whole name, she's mysterious, she's iconic, she doesn't need a subtitle 👑
🌸 SYNOPSIS 🌸
📖 Detailed Description
okay so picture this: at this point you should already have the GNU tools configured, built, and installed on your system. Like, all of them. Done. Dusted. ✨
In this chapter we present a simple example of using the GNU tools in an AVR project. And after you read this chapter, you should have a wayyy better feel for how the tools actually get used, and how a Makefile can be configured. no cap. 🫶
🎀 The Project
so the vibe is: this project uses the pulse-width modulator (PWM) to ramp an LED on and off every two seconds. every two seconds!! a whole little breathing light. adorable. 💅
The controller is an AT90S2313 processor. The circuit for this demonstration is shown in the schematic diagram. And hey — if you happen to have a development kit, you should be able to just use that instead of building the circuit yourself for this project. work smarter not harder, periodt. 🦋
⚠️ Note: meanwhile, the AT90S2313 became obsolete. so either use its successor, the (pin-compatible) ATtiny2313 for the project, or maybe the ATmega8 or one of its successors (ATmega48/88/168) which have become quite popular since the original demo project had been established. For all these more modern devices, it is no longer necessary to use an external crystal for clocking, because they ship with the internal 1 MHz oscillator enabled — soC1,C2, andQ1can be omitted. Normally, for this experiment, the external circuitry on/RESET(R1,C3) can be omitted as well, leaving only the AVR, the LED, the bypass capacitorC4, and perhapsR2. For the ATmega8/48/88/168, use PB1 (pin 15 at the DIP-28 package) to connect the LED to. Additionally, this demo has been ported to many different other AVRs. The location of the respective OC pin varies between different AVRs, and it is mandated by the AVR hardware.
🖼️ Schematic of circuit for demo project — and fr fr the page prints this caption twice, back to back with zero space between them: Schematic of circuit for demo projectSchematic of circuit for demo project. iconic behavior honestly 😭
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]: as the AVR microcontroller series has been developed during the past years, new features have been added over time. Even though the basic concepts of the timer/counter1 are still the same as they used to be back in early 2001 when this simple demo was written initially, the names of registers and bits have been changed slightly to reflect the new features. Also, the port and pin mapping of the output compare match 1A (or 1 for older devices) pin which is used to control the LED varies between different AVRs. The fileiocompat.htries to abstract between all these differences using some preprocessor#ifdefstatements, so the actual program itself can operate on a common set of symbolic names. The macros defined by that file are:
OCR— the name of the OCR register used to control the PWM (usually eitherOCR1orOCR1A)DDROC— the name of the DDR (data direction register) for the OC outputOC1— the pin number of the OC1[A] output within its portTIMER1_TOP— the TOP value of the timer used for the PWM (1023for 10-bit PWMs,255for 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 modeTIMER1_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]:ISR()is a macro that marks the function as an interrupt routine. In this case, the function will get called when timer 1 overflows. Setting up interrupts is explained in greater detail in<avr/interrupt.h>: Interrupts.
🌈 Note [3]: the PWM is being used in 10-bit mode, so we need a 16-bit variable to remember the current value.
✨ Note [4]: this section determines the new value of the PWM.
🔥 Note [5]: here's where the newly computed value is loaded into the PWM register. Since we are in an interrupt routine, it is safe to use a 16-bit assignment to the register. Outside of an interrupt, the assignment should only be performed with interrupts disabled if there's a chance that an interrupt routine could also access this register (or another register that uses TEMP), see the appropriate FAQ entry.
🎀 Note [6]: this routine gets called after a reset. It initializes the PWM and enables interrupts.
💅 Note [7]: the main loop of the program does nothing — all the work is done by the interrupt routine! The sleep_mode() puts the processor on sleep until the next interrupt, to conserve power. Of course, that probably won't be noticable as we are still driving a LED, it is merely mentioned here to demonstrate the basic principle.
🌸 Note [8]: early AVR devices saturate their outputs at rather low currents when sourcing current, so the LED can be connected directly, and the resulting current through the LED will be about 15 mA. For modern parts (at least for the ATmega 128), however, Atmel has drastically increased the IO source capability, so when operating at 5 V Vcc, R2 is needed. Its value should be about 150 Ohms. When operating the circuit at 3 V, it can still be omitted though.
🦋 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: demo.c 1637 2008-03-17 21:49:41Z joerg_wunsch $
*/
#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
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.cThe 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.oIt 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. 💀
🫶 bestie we are SO not done here — more of this page is coming, don't you dare close the tab 💅
🔍 Examining the Object File 🔍
okay so bestie we have a binary file now ✨ but like… can we actually do anything useful with it, other than just shoving it straight into the processor? 🙈 turns out yes, and it's giving toolbox era.
The GNU Binutils suite is made up of a whole bunch of genuinely useful tools for messing with the object files that get generated. One of them is avr-objdump, which scoops info out of the object file and shows it to you in many useful ways. If you just type the command all by itself with no arguments, it'll list out its options for you. cute, right? 💅
So for instance, if you wanna get a feel for how big your application actually is, you can use the -h option. Its output shows how much space is used in each of the sections. and lowkey important: the .stab and .stabstr sections are the ones holding the debugging information, and they won't make it into the ROM file — so don't panic when the numbers look thicc. 🫶
An even more useful option is -S. This one disassembles the binary file and intersperses the source code right there in the output!! 😭✨ And fr fr, the author's opinion is that this method is way better than using -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 this option generates reflects the actual code that the processor will run. no cap. 👑
$ avr-objdump -h -S demo.elf > demo.lstHere'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 000000d8 00000000 00000000 00000094 2**1
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .data 00000000 00800060 000000d8 0000016c 2**0
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000003 00800060 00800060 0000016c 2**0
ALLOC
3 .stab 00000354 00000000 00000000 0000016c 2**2
CONTENTS, READONLY, DEBUGGING
4 .stabstr 000001ce 00000000 00000000 000004c0 2**0
CONTENTS, READONLY, DEBUGGING
5 .comment 00000012 00000000 00000000 0000068e 2**0
CONTENTS, READONLY
6 .note.gnu.avr.deviceinfo 0000003c 00000000 00000000 000006a0 2**2
CONTENTS, READONLY
7 .debug_info 0000048c 00000000 00000000 000006dc 2**0
CONTENTS, READONLY, DEBUGGING
8 .debug_abbrev 0000044e 00000000 00000000 00000b68 2**0
CONTENTS, READONLY, DEBUGGING
9 .debug_line 0000001d 00000000 00000000 00000fb6 2**0
CONTENTS, READONLY, DEBUGGING
10 .debug_str 0000017a 00000000 00000000 00000fd3 2**0
CONTENTS, READONLY, DEBUGGINGDisassembly of section .text:
00000000 <__vectors>:
0: 12 c0 rjmp .+36 ; 0x26 <__ctors_end>
2: 21 c0 rjmp .+66 ; 0x46 <__bad_interrupt>
4: 20 c0 rjmp .+64 ; 0x46 <__bad_interrupt>
6: 1f c0 rjmp .+62 ; 0x46 <__bad_interrupt>
8: 1e c0 rjmp .+60 ; 0x46 <__bad_interrupt>
a: 1d c0 rjmp .+58 ; 0x46 <__bad_interrupt>
c: 1c c0 rjmp .+56 ; 0x46 <__bad_interrupt>
e: 1b c0 rjmp .+54 ; 0x46 <__bad_interrupt>
10: 1b c0 rjmp .+54 ; 0x48 <__vector_8>
12: 19 c0 rjmp .+50 ; 0x46 <__bad_interrupt>
14: 18 c0 rjmp .+48 ; 0x46 <__bad_interrupt>
16: 17 c0 rjmp .+46 ; 0x46 <__bad_interrupt>
18: 16 c0 rjmp .+44 ; 0x46 <__bad_interrupt>
1a: 15 c0 rjmp .+42 ; 0x46 <__bad_interrupt>
1c: 14 c0 rjmp .+40 ; 0x46 <__bad_interrupt>
1e: 13 c0 rjmp .+38 ; 0x46 <__bad_interrupt>
20: 12 c0 rjmp .+36 ; 0x46 <__bad_interrupt>
22: 11 c0 rjmp .+34 ; 0x46 <__bad_interrupt>
24: 10 c0 rjmp .+32 ; 0x46 <__bad_interrupt>
00000026 <__ctors_end>:
26: 11 24 eor r1, r1
28: 1f be out 0x3f, r1 ; 63
2a: cf e5 ldi r28, 0x5F ; 95
2c: d4 e0 ldi r29, 0x04 ; 4
2e: de bf out 0x3e, r29 ; 62
30: cd bf out 0x3d, r28 ; 61
00000032 <__do_clear_bss>:
32: 20 e0 ldi r18, 0x00 ; 0
34: a0 e6 ldi r26, 0x60 ; 96
36: b0 e0 ldi r27, 0x00 ; 0
38: 01 c0 rjmp .+2 ; 0x3c <.do_clear_bss_start>
0000003a <.do_clear_bss_loop>:
3a: 1d 92 st X+, r1
0000003c <.do_clear_bss_start>:
3c: a3 36 cpi r26, 0x63 ; 99
3e: b2 07 cpc r27, r18
40: e1 f7 brne .-8 ; 0x3a <.do_clear_bss_loop>
42: 3f d0 rcall .+126 ; 0xc2 <main>
44: 47 c0 rjmp .+142 ; 0xd4 <_exit>
00000046 <__bad_interrupt>:
46: dc cf rjmp .-72 ; 0x0 <__vectors>
00000048 <__vector_8>:
#include "iocompat.h" /* Note [1] */
enum { UP, DOWN };
ISR (TIMER1_OVF_vect) /* Note [2] */
{
48: 1f 92 push r1
4a: 1f b6 in r1, 0x3f ; 63
4c: 1f 92 push r1
4e: 11 24 eor r1, r1
50: 2f 93 push r18
52: 8f 93 push r24
54: 9f 93 push r25
static uint16_t pwm; /* Note [3] */
static uint8_t direction;
switch (direction) /* Note [4] */
56: 20 91 62 00 lds r18, 0x0062 ; 0x800062 <direction.1>
{
case UP:
if (++pwm == TIMER1_TOP)
5a: 80 91 60 00 lds r24, 0x0060 ; 0x800060 <_edata>
5e: 90 91 61 00 lds r25, 0x0061 ; 0x800061 <_edata+0x1>
switch (direction) /* Note [4] */
62: 22 23 and r18, r18
64: a1 f0 breq .+40 ; 0x8e <__vector_8+0x46>
66: 21 30 cpi r18, 0x01 ; 1
68: 49 f4 brne .+18 ; 0x7c <__vector_8+0x34>
direction = DOWN;
break;
case DOWN:
if (--pwm == 0)
6a: 01 97 sbiw r24, 0x01 ; 1
6c: 90 93 61 00 sts 0x0061, r25 ; 0x800061 <_edata+0x1>
70: 80 93 60 00 sts 0x0060, r24 ; 0x800060 <_edata>
74: 00 97 sbiw r24, 0x00 ; 0
76: 11 f4 brne .+4 ; 0x7c <__vector_8+0x34>
direction = UP;
78: 10 92 62 00 sts 0x0062, r1 ; 0x800062 <direction.1>
break;
}
OCR = pwm; /* Note [5] */
7c: 9b bd out 0x2b, r25 ; 43
7e: 8a bd out 0x2a, r24 ; 42
}
80: 9f 91 pop r25
82: 8f 91 pop r24
84: 2f 91 pop r18
86: 1f 90 pop r1
88: 1f be out 0x3f, r1 ; 63
8a: 1f 90 pop r1
8c: 18 95 reti
if (++pwm == TIMER1_TOP)
8e: 01 96 adiw r24, 0x01 ; 1
90: 90 93 61 00 sts 0x0061, r25 ; 0x800061 <_edata+0x1>
94: 80 93 60 00 sts 0x0060, r24 ; 0x800060 <_edata>
98: 8f 3f cpi r24, 0xFF ; 255
9a: 23 e0 ldi r18, 0x03 ; 3
9c: 92 07 cpc r25, r18
9e: 71 f7 brne .-36 ; 0x7c <__vector_8+0x34>
direction = DOWN;
a0: 21 e0 ldi r18, 0x01 ; 1
a2: 20 93 62 00 sts 0x0062, r18 ; 0x800062 <direction.1>
a6: ea cf rjmp .-44 ; 0x7c <__vector_8+0x34>
000000a8 <ioinit>:
void
ioinit (void) /* Note [6] */
{
/* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */
TCCR1A = TIMER1_PWM_INIT;
a8: 83 e8 ldi r24, 0x83 ; 131
aa: 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;
ac: 8e b5 in r24, 0x2e ; 46
ae: 81 60 ori r24, 0x01 ; 1
b0: 8e bd out 0x2e, r24 ; 46
#if defined(TIMER1_SETUP_HOOK)
TIMER1_SETUP_HOOK();
#endif
/* Set PWM value to 0. */
OCR = 0;
b2: 1b bc out 0x2b, r1 ; 43
b4: 1a bc out 0x2a, r1 ; 42
/* Enable OC1 as output. */
DDROC = _BV (OC1);
b6: 82 e0 ldi r24, 0x02 ; 2
b8: 87 bb out 0x17, r24 ; 23
/* Enable timer 1 overflow interrupt. */
TIMSK = _BV (TOIE1);
ba: 84 e0 ldi r24, 0x04 ; 4
bc: 89 bf out 0x39, r24 ; 57
sei ();
be: 78 94 sei
}
c0: 08 95 ret
000000c2 <main>:
int
main (void)
{
ioinit ();
c2: f2 df rcall .-28 ; 0xa8 <ioinit>
/* loop forever, the interrupts are doing the rest */
for (;;) /* Note [7] */
sleep_mode();
c4: 85 b7 in r24, 0x35 ; 53
c6: 80 68 ori r24, 0x80 ; 128
c8: 85 bf out 0x35, r24 ; 53
ca: 88 95 sleep
cc: 85 b7 in r24, 0x35 ; 53
ce: 8f 77 andi r24, 0x7F ; 127
d0: 85 bf out 0x35, r24 ; 53
d2: f8 cf rjmp .-16 ; 0xc4 <main+0x2>
000000d4 <_exit>:
d4: f8 94 cli
000000d6 <__stop_program>:
d6: ff cf rjmp .-2 ; 0xd6 <__stop_program>like, hello?? 😭 the source code is right there next to the instructions. it's giving best of both worlds. and notice how the vector table got expanded for you too, which the compiler-only listing wouldn't do — that's the whole point the author was making. 💖
🌸 Linker Map Files 🌸
okay so avr-objdump is super useful, but sometimes you <em>really</em> need to see info about the link that can only be generated by the linker. That's where a map file comes in, bestie. A map file contains this information. It 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.oSome points of interest in the demo.map file are:
.rela.plt
*(.rela.plt)
.text 0x0000000000000000 0xd8
*(.vectors)
.vectors 0x0000000000000000 0x26 /usr/local/lib/gcc/avr/10.2.0/../../../../avr/lib/avr4/crtatmega8.o
0x0000000000000000 __vectors
0x0000000000000000 __vector_default
*(.vectors)
*(.progmem.gcc*)
0x0000000000000026 . = ALIGN (0x2)
0x0000000000000026 __trampolines_start = .
*(.trampolines)
.trampolines 0x0000000000000026 0x0 linker stubs
*(.trampolines*)
0x0000000000000026 __trampolines_end = .
*libprintf_flt.a:*(.progmem.data)
*libc.a:*(.progmem.data)
*(.progmem.*)
0x0000000000000026 . = ALIGN (0x2)
*(.lowtext)
*(.lowtext*)
0x0000000000000026 __ctors_start = .The .text segment (where program instructions are stored) starts at location 0x0.
*(.fini2)
*(.fini2)
*(.fini1)
*(.fini1)
*(.fini0)
.fini0 0x00000000000000d4 0x4 /usr/local/lib/gcc/avr/10.2.0/avr4/libgcc.a(_exit.o)
*(.fini0)
*(.hightext)
*(.hightext*)
*(.progmemx.*)
0x00000000000000d8 . = ALIGN (0x2)
*(.jumptables)
*(.jumptables*)
0x00000000000000d8 _etext = ..data 0x0000000000800060 0x0 load address 0x00000000000000d8
[!provide] PROVIDE (__data_start = .)
*(.data)
.data 0x0000000000800060 0x0 /usr/local/lib/gcc/avr/10.2.0/../../../../avr/lib/avr4/crtatmega8.o
.data 0x0000000000800060 0x0 demo.o
.data 0x0000000000800060 0x0 /usr/local/lib/gcc/avr/10.2.0/avr4/libgcc.a(_exit.o)
.data 0x0000000000800060 0x0 /usr/local/lib/gcc/avr/10.2.0/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 0x0 /usr/local/lib/gcc/avr/10.2.0/../../../../avr/lib/avr4/crtatmega8.o
.bss 0x0000000000800060 0x3 demo.o
.bss 0x0000000000800063 0x0 /usr/local/lib/gcc/avr/10.2.0/avr4/libgcc.a(_exit.o)
.bss 0x0000000000800063 0x0 /usr/local/lib/gcc/avr/10.2.0/avr4/libgcc.a(_clear_bss.o)
*(.bss*)
*(COMMON)
0x0000000000800063 PROVIDE (__bss_end = .)
0x00000000000000d8 __data_load_start = LOADADDR (.data)
0x00000000000000d8 __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
.textsegment is location0x114( denoted by_etext), so the instructions use up276bytes of FLASH. - The
.datasegment (where initialized static variables are stored) starts at location0x60, which is the first address after the register bank on an ATmega8 processor. - The next available address in the
.datasegment is also location0x60, so the application has no initialized data. - The
.bsssegment (where uninitialized data is stored) starts at location0x60. - The next available address in the
.bsssegment is location0x63, so the application uses3bytes of uninitialized data. - The
.eepromsegment (where EEPROM variables are stored) starts at location0x0. - The next available address in the
.eepromsegment is also location0x0, 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.hexThe resulting demo.hex file contains:
:1000000012C021C020C01FC01EC01DC01CC01BC00C
:100010001BC019C018C017C016C015C014C013C02B
:1000200012C011C010C011241FBECFE5D4E0DEBF46
:10003000CDBF20E0A0E6B0E001C01D92A336B2071C
:10004000E1F73FD047C0DCCF1F921FB61F921124AB
:100050002F938F939F9320916200809160009091E5
:1000600061002223A1F0213049F4019790936100AF
:1000700080936000009711F4109262009BBD8ABDCE
:100080009F918F912F911F901FBE1F9018950196E1
:1000900090936100809360008F3F23E0920771F797
:1000A00021E020936200EACF83E88FBD8EB58160A6
:1000B0008EBD1BBC1ABC82E087BB84E089BF7894EC
:1000C0000895F2DF85B7806885BF889585B78F77FB
:0800D00085BFF8CFF894FFCFC3
:00000001FFThe -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.hexThere 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 💅
Okay bestie, real talk: typing all those commands over and over is so not the vibe. 😭 So instead, you just put them all in a make file. To build the demo project using make, save the following in a file called Makefile:
Note: ThisMakefilecan only be used as input for the GNU version ofmake. That's it, that's the rule. 🚫
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 📚
Yep, that's the section, bestie — the source code is right there if you wanna go peek at it. 👀
👑 Author 💖
Generated automatically by Doxygen for avr-libc from the source code. No human wrote this one, it just manifested. ✨
And that's a wrap on the whole thing, bestie!! 🎀 This was Version 2.1.0, dated Sat Jan 29 2022, and you've officially made it to the end of the demo_project(3) page. 🦋 You ate that, fr fr. Go build something iconic. 💅👑
📦 where this page comes from
- fedora 43: avr-libc 2.2.1-3.fc43 · BSD-3-Clause
- fedora 44: avr-libc 2.2.1-5.fc44 · BSD-3-Clause
- opensuse-leap 16.0: avr-libc 2.1.0-bp160.1.33 · BSD-3-Clause
- 💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on : a language model's rewrite of the original, under its terms