py_ext.c

/*
 * Python Asynchronous execution code
 *
 * PLC put python commands in a fifo, respecting execution order
 * with the help of C pragmas inserted in python_eval FB code
 *
 * Buffer content is read asynchronously, (from non real time part),
 * commands are executed and result stored for later use by PLC.
 *
 * In this implementation, fifo is a list of pointer to python_eval
 * function blocks structures. Some local variables have been added in
 * python_eval interface. We use those local variables as buffer and state
 * flags.
 *
 * */

#include "iec_types_all.h"
#include "POUS.h"
#include <string.h>

/* The fifo (fixed size, as number of FB is fixed) */
static PYTHON_EVAL* EvalFBs[1];
/* Producer and consumer cursors */
static int Current_PLC_EvalFB;
static int Current_Python_EvalFB;

/* A global IEC-Python gateway state, for use inside python_eval FBs*/
static int PythonState;
#define PYTHON_LOCKED_BY_PYTHON 0
#define PYTHON_LOCKED_BY_PLC 1
#define PYTHON_MUSTWAKEUP 2
#define PYTHON_FINISHED 4

/* Each python_eval FunctionBlock have it own state */
#define PYTHON_FB_FREE 0
#define PYTHON_FB_REQUESTED 1
#define PYTHON_FB_PROCESSING 2
#define PYTHON_FB_ANSWERED 3

int WaitPythonCommands(void);
void UnBlockPythonCommands(void);
int TryLockPython(void);
void UnLockPython(void);
void LockPython(void);

int __init_py_ext()
{
	int i;
	/* Initialize cursors */
	Current_Python_EvalFB = 0;
	Current_PLC_EvalFB = 0;
	PythonState = PYTHON_LOCKED_BY_PYTHON;
	for(i = 0; i < 1; i++)
		EvalFBs[i] = NULL;
  return 0;
}

void __cleanup_py_ext()
{
	PythonState = PYTHON_FINISHED;
	UnBlockPythonCommands();
}

void __retrieve_py_ext()
{
	/* Check Python thread is not being
	 * modifying internal python_eval data */
	PythonState = TryLockPython() ?
	                PYTHON_LOCKED_BY_PLC :
	                PYTHON_LOCKED_BY_PYTHON;
	/* If python thread _is_ in, then PythonState remains PYTHON_LOCKED_BY_PYTHON
	 * and python_eval will no do anything */
}

void __publish_py_ext()
{
	if(PythonState & PYTHON_LOCKED_BY_PLC){
		/* If runnig PLC did push something in the fifo*/
		if(PythonState & PYTHON_MUSTWAKEUP){
			/* WakeUp python thread */
			UnBlockPythonCommands();
		}
		UnLockPython();
	}
}
/**
 * Called by the PLC, each time a python_eval
 * FB instance is executed
 */
void __PythonEvalFB(int poll, PYTHON_EVAL* data__)
{
    if(!__GET_VAR(data__->TRIG)){
        /* ACK is False when TRIG is false, except a pulse when receiving result */
        __SET_VAR(data__->, ACK,, 0);
    }
	/* detect rising edge on TRIG to trigger evaluation */
	if(((__GET_VAR(data__->TRIG) && !__GET_VAR(data__->TRIGM1)) ||
	   /* polling is equivalent to trig on value rather than on rising edge*/
	    (poll && __GET_VAR(data__->TRIG) )) &&
	    /* trig only if not already trigged */
	    __GET_VAR(data__->TRIGGED) == 0){
		/* mark as trigged */
	    __SET_VAR(data__->, TRIGGED,, 1);
		/* make a safe copy of the code */
		__SET_VAR(data__->, PREBUFFER,, __GET_VAR(data__->CODE));
	}
	/* retain value for next rising edge detection */
	__SET_VAR(data__->, TRIGM1,, __GET_VAR(data__->TRIG));

	/* python thread is not in ? */
	if( PythonState & PYTHON_LOCKED_BY_PLC){
		/* if some answer are waiting, publish*/
		if(__GET_VAR(data__->STATE) == PYTHON_FB_ANSWERED){
			/* Copy buffer content into result*/
			__SET_VAR(data__->, RESULT,, __GET_VAR(data__->BUFFER));
			/* signal result presence to PLC*/
			__SET_VAR(data__->, ACK,, 1);
			/* Mark as free */
			__SET_VAR(data__->, STATE,, PYTHON_FB_FREE);
			/* mark as not trigged */
			if(!poll)
			    __SET_VAR(data__->, TRIGGED,, 0);
			/*printf("__PythonEvalFB pop %d - %*s\n",Current_PLC_EvalFB, data__->BUFFER.len, data__->BUFFER.body);*/
		}else if(poll){
			/* when in polling, no answer == ack down */
		    __SET_VAR(data__->, ACK,, 0);
		}
		/* got the order to act ?*/
		if(__GET_VAR(data__->TRIGGED) == 1 &&
		   /* and not already being processed */
		   __GET_VAR(data__->STATE) == PYTHON_FB_FREE)
		{
			/* Enter the block in the fifo
			 * Don't have to check if fifo cell is free
			 * as fifo size == FB count, and a FB cannot
			 * be requested twice */
			EvalFBs[Current_PLC_EvalFB] = data__;
			/* copy into BUFFER local*/
			__SET_VAR(data__->, BUFFER,, __GET_VAR(data__->PREBUFFER));
			/* Set ACK pin to low so that we can set a rising edge on result */
			if(!poll){
				/* when not polling, a new answer imply reseting ack*/
			    __SET_VAR(data__->, ACK,, 0);
			}else{
				/* when in polling, acting reset trigger */
			    __SET_VAR(data__->, TRIGGED,, 0);
			}
			/* Mark FB busy */
			__SET_VAR(data__->, STATE,, PYTHON_FB_REQUESTED);
			/* Have to wakeup python thread in case he was asleep */
			PythonState |= PYTHON_MUSTWAKEUP;
			/*printf("__PythonEvalFB push %d - %*s\n",Current_PLC_EvalFB, data__->BUFFER.len, data__->BUFFER.body);*/
			/* Get a new line */
			Current_PLC_EvalFB = (Current_PLC_EvalFB + 1) % 1;
		}
	}
}

char* PythonIterator(char* result, void** id)
{
	char* next_command;
	PYTHON_EVAL* data__;
	//printf("PythonIterator result %s\n", result);
    /*emergency exit*/
    if(PythonState & PYTHON_FINISHED) return NULL;
	/* take python mutex to prevent changing PLC data while PLC running */
	LockPython();
	/* Get current FB */
	data__ = EvalFBs[Current_Python_EvalFB];
	if(data__ && /* may be null at first run */
	    __GET_VAR(data__->STATE) == PYTHON_FB_PROCESSING){ /* some answer awaited*/
	   	/* If result not None */
	   	if(result){
			/* Get results len */
	   	    __SET_VAR(data__->, BUFFER, .len, strlen(result));
			/* prevent results overrun */
			if(__GET_VAR(data__->BUFFER, .len) > STR_MAX_LEN)
			{
			    __SET_VAR(data__->, BUFFER, .len, STR_MAX_LEN);
				/* TODO : signal error */
			}
			/* Copy results to buffer */
			strncpy((char*)__GET_VAR(data__->BUFFER, .body), result, __GET_VAR(data__->BUFFER,.len));
	   	}else{
	   	    __SET_VAR(data__->, BUFFER, .len, 0);
	   	}
		/* remove block from fifo*/
		EvalFBs[Current_Python_EvalFB] = NULL;
		/* Mark block as answered */
		__SET_VAR(data__->, STATE,, PYTHON_FB_ANSWERED);
		/* Get a new line */
		Current_Python_EvalFB = (Current_Python_EvalFB + 1) % 1;
		//printf("PythonIterator ++ Current_Python_EvalFB %d\n", Current_Python_EvalFB);
	}
	/* while next slot is empty */
	while(((data__ = EvalFBs[Current_Python_EvalFB]) == NULL) ||
	 	  /* or doesn't contain command */
	      __GET_VAR(data__->STATE) != PYTHON_FB_REQUESTED)
	{
		UnLockPython();
		/* wait next FB to eval */
		//printf("PythonIterator wait\n");
		if(WaitPythonCommands()) return NULL;
		/*emergency exit*/
		if(PythonState & PYTHON_FINISHED) return NULL;
		LockPython();
	}
	/* Mark block as processing */
	__SET_VAR(data__->, STATE,, PYTHON_FB_PROCESSING);
	//printf("PythonIterator\n");
	/* make BUFFER a null terminated string */
	__SET_VAR(data__->, BUFFER, .body[__GET_VAR(data__->BUFFER, .len)], 0);
	/* next command is BUFFER */
	next_command = (char*)__GET_VAR(data__->BUFFER, .body);
	*id=data__;
	/* free python mutex */
	UnLockPython();
	/* return the next command to eval */
	return next_command;
}