| ??? 04/21/07 08:43 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#137692 - SDCC also Responding to: ???'s previous message |
From the manual
Some architectures (mcs51/ds390) have an atomic bit test and clear instruction.
These type of instructions are typically used in preemptive multitasking systems,
where a routine f.e. claims the use of a data structure ('acquires a lock on it'),
makes some modifications and then releases the lock when the data structure is consistent again.
The instruction may also be used if interrupt and non-interrupt code have to compete for a resource.
With the atomic bit test and clear instruction interrupts don't have to be disabled for the locking operation.
SDCC generates this instruction if the source follows this pattern:
volatile bit resource_is_free;
if (resource_is_free)
{
resource_is_free=0;
...
resource_is_free=1;
}
Note, mcs51 and ds390 support only an atomic bit test and clear instruction (as opposed to atomic bit test and set).
to be found at http://sdcc.sourceforge.net/doc/sdccm...ode72.html regards Patrick |
| Topic | Author | Date |
| lesson learned | 01/01/70 00:00 | |
| "atomic" | 01/01/70 00:00 | |
| atomicity | 01/01/70 00:00 | |
| if thatb is so | 01/01/70 00:00 | |
| Indeed | 01/01/70 00:00 | |
| Bit test and clear | 01/01/70 00:00 | |
| JBC | 01/01/70 00:00 | |
| favourite atomic test-and-set instructions | 01/01/70 00:00 | |
| SDCC also | 01/01/70 00:00 | |
| Classic atomic problem | 01/01/70 00:00 | |
| and/or ... | 01/01/70 00:00 | |
another example | 01/01/70 00:00 |