Karl Zweimüller
/
LcdWindow
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Fork of
LcdWindow
by 
Hendrik Lipka
semaphore.cpp@3:e5d5e2fe4bf6, 2010-11-28 (annotated)
- Committer:
- hlipka
- Date:
- Sun Nov 28 22:09:54 2010 +0000
- Revision:
- 3:e5d5e2fe4bf6
- Child:
- 9:2fe93daa2106
Made LCD driver thread safe (to allow usage from timers)
Who changed what in which revision?
| User | Revision | Line number | New contents of line |
|---|---|---|---|
| hlipka | 3:e5d5e2fe4bf6 | 1 | /** |
| hlipka | 3:e5d5e2fe4bf6 | 2 | * code from Igor Skochinsky |
| hlipka | 3:e5d5e2fe4bf6 | 3 | * taken from http://mbed.org/forum/mbed/post/799/ |
| hlipka | 3:e5d5e2fe4bf6 | 4 | */ |
| hlipka | 3:e5d5e2fe4bf6 | 5 | |
| hlipka | 3:e5d5e2fe4bf6 | 6 | #include "semaphore.h" |
| hlipka | 3:e5d5e2fe4bf6 | 7 | |
| hlipka | 3:e5d5e2fe4bf6 | 8 | Semaphore::Semaphore(): s(SemFree) {}; |
| hlipka | 3:e5d5e2fe4bf6 | 9 | |
| hlipka | 3:e5d5e2fe4bf6 | 10 | bool Semaphore::take(bool block) |
| hlipka | 3:e5d5e2fe4bf6 | 11 | { |
| hlipka | 3:e5d5e2fe4bf6 | 12 | int oldval; |
| hlipka | 3:e5d5e2fe4bf6 | 13 | #if defined(TARGET_LPC1768) // on Cortex-M3 we can use ldrex/strex |
| hlipka | 3:e5d5e2fe4bf6 | 14 | do { |
| hlipka | 3:e5d5e2fe4bf6 | 15 | // read the semaphore value |
| hlipka | 3:e5d5e2fe4bf6 | 16 | oldval = __ldrex(&s); |
| hlipka | 3:e5d5e2fe4bf6 | 17 | // loop again if it is locked and we are blocking |
| hlipka | 3:e5d5e2fe4bf6 | 18 | // or setting it with strex failed |
| hlipka | 3:e5d5e2fe4bf6 | 19 | } |
| hlipka | 3:e5d5e2fe4bf6 | 20 | while ( (block && oldval == SemTaken) || __strex(SemTaken, &s) != 0 ); |
| hlipka | 3:e5d5e2fe4bf6 | 21 | if ( !block ) __clrex(); // clear exclusive lock set by ldrex |
| hlipka | 3:e5d5e2fe4bf6 | 22 | #else // on arm7 there's only swp |
| hlipka | 3:e5d5e2fe4bf6 | 23 | do { |
| hlipka | 3:e5d5e2fe4bf6 | 24 | // swp sets the pointed data to the given value and returns the previous one |
| hlipka | 3:e5d5e2fe4bf6 | 25 | oldval = __swp(SemTaken, &s); |
| hlipka | 3:e5d5e2fe4bf6 | 26 | // if blocking, loop until the previous value becomes 0 |
| hlipka | 3:e5d5e2fe4bf6 | 27 | // which would mean we have successfully taken the lock |
| hlipka | 3:e5d5e2fe4bf6 | 28 | } |
| hlipka | 3:e5d5e2fe4bf6 | 29 | while (block && oldval == SemTaken); |
| hlipka | 3:e5d5e2fe4bf6 | 30 | #endif |
| hlipka | 3:e5d5e2fe4bf6 | 31 | return oldval == SemFree; |
| hlipka | 3:e5d5e2fe4bf6 | 32 | } |
| hlipka | 3:e5d5e2fe4bf6 | 33 | |
| hlipka | 3:e5d5e2fe4bf6 | 34 | // release the semaphore |
| hlipka | 3:e5d5e2fe4bf6 | 35 | void Semaphore::release() |
| hlipka | 3:e5d5e2fe4bf6 | 36 | { |
| hlipka | 3:e5d5e2fe4bf6 | 37 | s = SemFree; |
| hlipka | 3:e5d5e2fe4bf6 | 38 | } |
| hlipka | 3:e5d5e2fe4bf6 | 39 |