Embedded Programming
Goals
- Read a microcontroller data sheet
- Program your board to do something, with as many different programming languages and programming environments as possible
- Optionally, experiment with other architectures
Programming my board
First of all I tried to fix the board I made in week 06, manually cutting the traces with a xacto knife: an ill-fated move on my part, for my hand slipped and I damaged my pcb beyond hope for repair.
I made a new board, taking the chance to expose both the remaining pins on my ATtiny44.
With my board finally soldered I wrote a couple lines of C to make my led blink
#include < avr/io.h>
#include < util/delay.h>
int main(void) {
/* init */
DDRB = (1 << 2);
/* loop */
while (1) {
PORTB = (1 << 2);
_delay_ms(100);
PORTB = (0 << 2);
_delay_ms(100);
}
return 0;
}
The code is trivial and pretty much self-explanatory, nonetheless bear with me breaking it down a bit, in order to introduce some basic concept about avr programming.
The first 2 lines include system-wide headers files (more here), in line 6 I set PB2 (the led pin) as a generic digital output writing a 1 its Data Direction Register (Datasheep, par 10.1.1, p. 54), using bit shifting instead of writing the whole byte. The main loop starts at line 9 with powering the led setting the relevant PORT as high, waiting a bit and switching the led off.
I then copied the default makefile avaible on the archive and deleted anything but the instruction related to my FabISP programmer, which left me with the following file (I also added a little clean instruction):
PROJECT=blink-simo
SOURCES=$(PROJECT).c
MMCU=attiny44
F_CPU = 20000000
CFLAGS=-mmcu=$(MMCU) -Wall -Os -DF_CPU=$(F_CPU)
$(PROJECT).hex: $(PROJECT).out
avr-objcopy -O ihex $(PROJECT).out $(PROJECT).c.hex;\
avr-size --mcu=$(MMCU) --format=avr $(PROJECT).out
$(PROJECT).out: $(SOURCES)
avr-gcc $(CFLAGS) -I./ -o $(PROJECT).out $(SOURCES)
program-usbtiny: $(PROJECT).hex
avrdude -p t44 -P usb -c usbtiny -U flash:w:$(PROJECT).c.hex
program-usbtiny-fuses: $(PROJECT).hex
avrdude -p t44 -P usb -c usbtiny -U lfuse:w:0x5E:m
clear:
rm -r $(PROJECT).c.hex $(PROJECT).out
The program-usbtiny-fuses left me a little puzzled, so I tried to figure out what it does. The avrdude manual tell me that this command is directly (the "m" option) writing a byte value ("01011110", in its hexadecimal notation "0x5e") in the low fuse byte, but after all this I was none the wiser; This tutorial pointed me to the right direction (and the right pages on the datasheet): this fuses configuration instructs the attiny to use the external 20MHz resonator as clock, instead of the internal one.
I connected my boards and, after a quick check to make sure the programmer was ready to work, I flashed my hello board:
sgrc@t420:~$ avrdude -p t44 -c usbtiny
avrdude: AVR device initialized and ready to accept instructions
Reading | ################################################## | 100% 0.00s
avrdude: Device signature = 0x1e9207 (probably t44)
avrdude: safemode: Fuses OK (E:FF, H:DF, L:62)
avrdude done. Thank you.
sgrc@t420:~$
sgrc@t420:~$
sgrc@t420:~$
sgrc@t420:~$ cd fabacademy2017/doc/week08/
AVR-Programming/ code/ files/ img/ schede/ terminale/
sgrc@t420:~$ cd fabacademy2017/doc/week08/code/blink-izi/
sgrc@t420:~/fabacademy2017/doc/week08/code/blink-izi$ ls
blinkled.c blink-simo.c Makefile
sgrc@t420:~/fabacademy2017/doc/week08/code/blink-izi$ make
avr-gcc -mmcu=attiny44 -Wall -Os -DF_CPU=20000000 -I./ -o blink-simo.out blink-simo.c
avr-objcopy -O ihex blink-simo.out blink-simo.c.hex;\
avr-size --mcu=attiny44 --format=avr blink-simo.out
AVR Memory Usage
----------------
Device: attiny44
Program: 82 bytes (2.0% Full)
(.text + .data + .bootloader)
Data: 0 bytes (0.0% Full)
(.data + .bss + .noinit)
sgrc@t420:~/fabacademy2017/doc/week08/code/blink-izi$ make program-
program-avrisp2 program-bsd program-dragon program-usbtiny
program-avrisp2-fuses program-dasa program-ice program-usbtiny-fuses
sgrc@t420:~/fabacademy2017/doc/week08/code/blink-izi$ make program-usbtiny-fuses
avr-objcopy -O ihex blink-simo.out blink-simo.c.hex;\
avr-size --mcu=attiny44 --format=avr blink-simo.out
AVR Memory Usage
----------------
Device: attiny44
Program: 82 bytes (2.0% Full)
(.text + .data + .bootloader)
Data: 0 bytes (0.0% Full)
(.data + .bss + .noinit)
avrdude -p t44 -P usb -c usbtiny -U lfuse:w:0x5E:m
avrdude: AVR device initialized and ready to accept instructions
Reading | ################################################## | 100% 0.00s
avrdude: Device signature = 0x1e9207 (probably t44)
avrdude: reading input file "0x5E"
avrdude: writing lfuse (1 bytes):
Writing | ################################################## | 100% 0.01s
avrdude: 1 bytes of lfuse written
avrdude: verifying lfuse memory against 0x5E:
avrdude: load data lfuse data from input file 0x5E:
avrdude: input file 0x5E contains 1 bytes
avrdude: reading on-chip lfuse data:
Reading | ################################################## | 100% 0.00s
avrdude: verifying ...
avrdude: 1 bytes of lfuse verified
avrdude: safemode: Fuses OK (E:FF, H:DF, L:5E)
avrdude done. Thank you.
sgrc@t420:~/fabacademy2017/doc/week08/code/blink-izi$ make program-usbtiny
avr-objcopy -O ihex blink-simo.out blink-simo.c.hex;\
avr-size --mcu=attiny44 --format=avr blink-simo.out
AVR Memory Usage
----------------
Device: attiny44
Program: 82 bytes (2.0% Full)
(.text + .data + .bootloader)
Data: 0 bytes (0.0% Full)
(.data + .bss + .noinit)
avrdude -p t44 -P usb -c usbtiny -U flash:w:blink-simo.c.hex
avrdude: AVR device initialized and ready to accept instructions
Reading | ################################################## | 100% 0.00s
avrdude: Device signature = 0x1e9207 (probably t44)
avrdude: NOTE: "flash" memory has been specified, an erase cycle will be performed
To disable this feature, specify the -D option.
avrdude: erasing chip
avrdude: reading input file "blink-simo.c.hex"
avrdude: input file blink-simo.c.hex auto detected as Intel Hex
avrdude: writing flash (82 bytes):
Writing | ################################################## | 100% 0.14s
avrdude: 82 bytes of flash written
avrdude: verifying flash memory against blink-simo.c.hex:
avrdude: load data flash data from input file blink-simo.c.hex:
avrdude: input file blink-simo.c.hex auto detected as Intel Hex
avrdude: input file blink-simo.c.hex contains 82 bytes
avrdude: reading on-chip flash data:
Reading | ################################################## | 100% 0.20s
avrdude: verifying ...
avrdude: 82 bytes of flash verified
avrdude: safemode: Fuses OK (E:FF, H:DF, L:5E)
avrdude done. Thank you.
And it blinks!
After this I wrote a simple code to make my led blink only after the button has been pressed
#include < avr/io.h>
#include < util/delay.h>
int main(void) {
/* inits */
DDRB = (1 << 2);
DDRA = (0 << 7);
PORTA = (1 << 7);
int x;
/* loop */
while (1) {
if (!(PINA & (1 << 7))) {
for (x=0; x<3; x++) {
PORTB = (1 << 2);
_delay_ms(50);
PORTB = (0 << 2);
_delay_ms(50);
}
}
else {
PORTB = (0 << 2);
}
}
return 0;
}
These are a couple of trivial examples, just to learn the ropes; I hope that, with a deeper understanding of the datasheet, I'll be able to code something more meaningful.
Links
- Make: AVR Programming - AVR programming 101. Great intro for this subject, wholeheartedly recommend
- AVR input/output tutorial
- Fuses - to understand Neil's Makefile
- hello-revisited.tar.gz - eagle working files
- hello-revisited-milling.tar.gz - png and rml files for milling the board