Chris O'Byrne - YAVRTOS
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Semaphores
Functions | |
| uint8_t | wait_for_min_value (semaphore_t *s, int16_t value) |
| Wait for a semaphore to reach at least a particular value. | |
| uint8_t | wait_for_increment_of (semaphore_t *p, uint16_t amount) |
| Wait for a semaphore to increment its value by a certain amount. | |
| int16_t | get_semaphore_value (semaphore_t *s) |
| Get the current value of a semaphore. | |
| void | increment_semaphore_by (semaphore_t *s, uint16_t amount) |
| Increment the value of a semaphore by the given amount. | |
Detailed Description
A semaphore contains a number that tasks can suspend themselves against, waiting for the number to reach at least a certain value before the task is schedulable again.To update a semaphore's value, use increment_semaphore_by()
To read a semaphore's value, use get_semaphore_value()
To lock on a semaphore, use wait_for_min_value() or wait_for_increment_of()
See using semaphores for information on how to use semaphores
Function Documentation
| int16_t get_semaphore_value | ( | semaphore_t * | s | ) |
Get the current value of a semaphore.
This function may be called anywhere
| void increment_semaphore_by | ( | semaphore_t * | s, | |
| uint16_t | amount | |||
| ) |
Increment the value of a semaphore by the given amount.
The arguments are
s- the semaphore to incrementamount- the amount by which the semaphore should be incremented. Note that semaphore values are actually signed 16-bit numbers, so the maximum value for this argument is about 32,000
When called from a task, this function may end up yielding control to a higher-priority task that is waiting on the semaphore.
| uint8_t wait_for_increment_of | ( | semaphore_t * | p, | |
| uint16_t | amount | |||
| ) |
Wait for a semaphore to increment its value by a certain amount.
The arguments are
p- the semaphore to wait onamount- the amount by which the semaphore should increment before returning. Note that semaphore values are actually signed 16-bit numbers, so the maximum value for this argument is about 32,000
| uint8_t wait_for_min_value | ( | semaphore_t * | s, | |
| int16_t | value | |||
| ) |
Wait for a semaphore to reach at least a particular value.
Since the calling task could be suspended, this can only be called by a task with a non-zero priority