As a fun way to improve my C, I started programming the Arduino using Atmel Studio instead of the friendlier Arduino IDE.<\/p>\n\n\n\n
Below is my very first program. It blinks a red LED and a white LED according to a preset pattern.<\/p>\n\n\n\n
#define F_CPU 16000000UL\n\n#include <avr\/io.h>\n#include <util\/delay.h>\n\nstruct Led\n{\n int pin;\n int blinks;\n int on_duration;\n int off_duration;\n};\n\nvoid delay_ms(int ms)\n{\n while (ms-- > 0) {\n _delay_ms(1);\n }\n}\n\nvoid blink(const struct Led* const led)\n{\n for (int i = 0; i < led->blinks; i++) {\n PORTB |= led->pin;\n delay_ms(led->on_duration);\n PORTB &= ~led->pin;\n delay_ms(led->off_duration);\n }\n}\n\nint main(void)\n{\n const struct Led white_led = { 1<<PB6, 10, 100, 500 };\n const struct Led red_led = { 1<<PB7, 10, 500, 1000 };\n\n DDRB |= white_led.pin;\n DDRB |= red_led.pin;\n while (1) {\n blink(&white_led);\n blink(&red_led);\n }\n}<\/pre>\n\n\n\nWith C in Atmel Studio and the AVR-LIBC library, IO ports are manipulated by changing bit patterns in the registers associated with the relevant ports. This requires a good understanding of bitwise operations in C despite the availability of macros to simplify the task.<\/p>\n\n\n\n
For example, to set pin 12 of the Arduino to output mode, bit 6 of register DDRB must be set to 1. To do so requires an |<\/code> (OR) operation with a bit pattern operand where bit 6 is set to 1 and the rest set to 0, so that the states of the other bits in the register are not disturbed.<\/p>\n\n\n\nUsing macros DDRB<\/code> and PB6<\/code> defined in AVR-LIBC, this is done like this: DDRB |= 1 << PB6<\/span> .<\/p>\n\n\n\nIf you are new to C and are unfamiliar with macros, you might wonder about that statement. Besides, DDRB<\/code> and PB6<\/code> are not referenced anywhere else in my program, so how does this line of code work?<\/p>\n\n\n\nDDRB<\/code> is a macro that expands into C code to dereference the address of the register associated with setting the mode for pin 12, and PB6<\/code> is just a symbolic constant for the value 6. In the statement above, by shifting the value 1 left by 6 positions, we create a new value which is then applied to the bit pattern stored at the dereferenced address with an |<\/code> operation to turn bit 6 of the register to 1. In this case, this sets pin 12 to output mode.<\/p>\n\n\n\nIn a nutshell, the sequence of operations is as follows.<\/p>\n\n\n\n
Step 1:<\/p>\n\n\n\n
1 << 6 = 01000000<\/pre>\n\n\n\nStep 2:<\/p>\n\n\n\n
Assuming the register DDRB is initially 00000001<\/code>:<\/p>\n\n\n\n00000001 | 01000000 = 01000001<\/pre>\n\n\n\nIn my C program, the result of step 1 is assigned to struct field Led.pin<\/code> and is used as the second operand for the operation in step 2.<\/p>\n\n\n\nIt took about an hour to refresh my knowledge of bitwise operations, but the real challenge was interpreting the Arduino schema<\/a> and the information in datasheets<\/a>, especially to find the right registers to manipulate.<\/p>\n","protected":false},"excerpt":{"rendered":"As a fun way to improve my C, I started programming the Arduino using Atmel Studio instead of the friendlier Arduino IDE. Below is my very first program. It blinks a red LED and a white LED according to a preset pattern. #define F_CPU 16000000UL #include <avr\/io.h> #include <util\/delay.h> struct Led { int pin; int […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-780","post","type-post","status-publish","format-standard","hentry","category-general"],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p3I4g9-cA","jetpack-related-posts":[],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/posts\/780","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/comments?post=780"}],"version-history":[{"count":25,"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/posts\/780\/revisions"}],"predecessor-version":[{"id":1316,"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/posts\/780\/revisions\/1316"}],"wp:attachment":[{"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/media?parent=780"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/categories?post=780"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/priscimon.net\/coding\/wp-json\/wp\/v2\/tags?post=780"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}