Etpu - Semaphores between Host and Etpu - MPC5746R

[demian91]

Hi im using the IDE CW eTPU 10.3 and S32DS 2.1 for the MPC5746R microcontroller.

Is it possible to use semaphores between the Host and the eTPU?. For the other hand, i understand that we have 4 semaphores in the eTPU between the two Engines A and B, only one sempahore can be active, but i not sure how is the syntax.

while(CC.SMLCK);
channel.SMPR = SMPR_LOCK_0;

//Code

channel.SMPR = SMPR_FREE;

Is that correct?

[johndiener]

The eTPU hardware semaphores are only for synchronization/resource protection between eTPU engines A and B. Host/eTPU coherency is supported for 2 parameters via the Coherent Dual-parameter Controller (host-side) or automatically via consecutive memory accesses (eTPU side). For more than 2 parameters techniques involving flagging or double-buffering and host service requests are typically employed.

As you state, only one semaphore can be locked by an eTPU engine at any one time. Thus if say engine B has semaphore 2 locked, and eTPU code running on this engine (B) executes "channel.SMPR = SMPR_LOCK_1", semaphore 2 is released, regardless of whether the take of semaphore 1 succeeded (engine A does NOT have semaphore 1 locked) or fails (engine A has semaphore 1 locked).

When locking a semaphore, code should be of the form:

  do { channel.SMPR = SMPR_LOCK_0; } while (CC.SMLCK);

As you note, to free the one locked semaphore (whichever it is), the code would be:

  channel.SMPR = SMPR_FREE;