Run multiple functions simultaneously with pic16f877a using C

Question

I am using microC to program pic16f877a to operate motors and solenoids. I have some functions making motors move at different space times eg motor1 moves for 100ms, stops, moves again for 100ms etc. for 4 loops, motor2 for 200ms and so on. I want these functions to start at the same time.

Think about a robot when you want to move its right hand up and down every 200ms for a total 2 mins and its left hand up and down every 400ms for a total again 2 mins. This process should start at the same time.

So basically I want to start something like :

start:
solenoid1 runs functionQuarter(moves up-down every x time) total like 2 mins
solenoid2 runs functionHalf(moves up-down every 2x time) total like 2 mins
stop

Is it possible to do this with micro c for this pic and how can I call 2 or more functions to start at the same time?

Answer 1

Why do you think you need threads? You know exactly when an operation should occur, so perform that operation exactly at that time. All you need is an appropriate scheduling system that helps you keep track of the operations. Compared to threads, you don't have the problem of unexpected scheduling, probably lower latency, no need for inter-thread synchronization.

Consider this sketch:

// this task structure says at what time to set 
// an output to a certain value
struct task {
    time_type when;
    output_type output;
    value_type value;
};

struct task_queue {
    struct task** tasks;
    size_t count;
};
void task_queue_push(struct task_queue* q, struct task* t);
struct task* task_queue_front(struct task_queue* q);
struct task* task_queue_pop(struct task_queue* q);

Now, in a loop, you keep looking at the first element in the queue and just sleep() until the start of the next task. Of course, that means you need to keep those tasks sorted by their start time! If multiple tasks start at the same time, you need to run them both, the only limit to "at the same time" the the execution time of each task. If necessary, as part of handling one task, you can create one or more other tasks. As a variation, you can also use a callback instead of just the output and value infos that assume you want to set some digital outputs only.

Answer 2

There isn't any solution for the pic16 series (it is far too small) but there is FreeRtos, made specifically for microcontrollers and there is a port for PIC18 (and a few others) check out the supported device list

Although freeRTOS is "free" to obtain and to use in personal projects I would recommend you purchase one of their books to help with implementation. There is free API on their site and demo code as well. It would be easier to understand it with the book (please note I am not tied to freeRTOS in anyway, I used it in projects with atmel controllers and found it very easy to use)

with freeRTOS you create a task (you define your solenoid control function) and then you set the priority, the delay then start the kernel. It's actually really straightforward.

Again, this won't work with your specific chip pic16, but if you can try another one, freeRTOS is a very well known and a pretty easy solution