How to use SCPI_ExprChannelListEntry()? about scpi-parser

[j123b567]

I think, that your example is wrong, because 1 has 1 dimension and 2!4 has 2 dimensions and there is not possible to create range : between different number of dimensions.

I will update documentation for this soon.

[koeart]

Hi,
I completely had the syntax wrong. Should've been READ? (@1,2,4). A better example would be MEAS:VOLT (@1,3,4:6), taken from SCPI99, Vol 1 Ch. 8.3.2 "Expressions - Channel Lists".

[j123b567]

OK, I don't have much time to write better documentation, so here are just small hints.

In handler of your command, read channel list as parameter using SCPI_Parameter.

scpi_parameter_t channel_list_param;

// get channel list
if (SCPI_Parameter(context, &channel_list_param, TRUE)) {
    scpi_expr_result_t res;
    scpi_bool_t is_range,
    int32_t values_from[4];
    int32_t values_to[4];
    size_t dimensions;

    // this is valid usage and it gets only real number of dimensions for the first item (index 0)
    res = SCPI_ExprChannelListEntry(context, &channel_list_param, 0, &is_range, NULL, NULL, 0, &dimensions);

    // this will fill values
    // if is_range, then both values_from and values_to are filled
    // dimensions represents number of items in this array. This number is always
    //    number of dimensions and can be larger then size of provided array, but provided array
    //    is filled only up to its size.
    res = SCPI_ExprChannelListEntry(context, &channel_list_param, 0, &is_range, values_from, values_to, 4, &dimensions);
}

You must iterate over all entries in the expression by changing index and chacking the result. If result is SCPI_EXPR_OK then all values are valid. If the result is SCPI_EXPR_ERROR, there was an error and you should stop handling this command.
If the result is SCPI_EXPR_NO_MORE then there are no more Entries in the list.

For channel list (@1,3,4:6), this will be result

• for index 0, is_range = false, values_from[0] = 1, dimensions = 1
• for index 1, is_range = false, values_from[0] = 3, dimensions = 1
• for index 2, is_range = true, values_from[0] = 4, values_to[0] = 6, dimensions = 1
• for index 3, result is SCPI_EXPR_NO_MORE

[koeart]

I coded a rather long example which handles different cases for channel numbers.
It works for (up to) 2 dimensions so far.
SCPI Vol says to parse ranges in order.
One enters ranges like this: (@rs!cs:re!ce), concatenating of ranges does work, too.
rs means "row start", re "row end", cs "column start", ce "column end".
Examples:
(@1!1:3!2) would be 1!1, 1!2, 2!1, 2!2, 3!1, 3!2.
(@3!1:1!3) would be 3!1, 3!2, 3!3, 2!1, 2!2, 2!3, ... 1!3.

In this example the whole channel list is written to array[] of dimensions maxrow x maxcol. Last values of array are {0, 0}. I introduced a datatype at the beginning to hold a value for row and column.

Hope this helps someone. Suggestions welcome!

struct _scpi_channel_value_t  {
   int32_t row;
   int32_t col;
};
typedef struct _scpi_channel_value_t scpi_channel_value_t;

/**
 * @brief 
 * parses lists
 * channel numbers > 0.
 * no checks yet.
 * valid: (@1), (@3!1:1:3,4), ...
 * 
 * @param channel_list channel list, compare to SCPI99 Vol 1 Ch. 8.3.2
 */
static scpi_result_t TEST_Chanlst ( scpi_t *context )
{
    scpi_parameter_t channel_list_param;
    #define maxrow 2    //maximum number of rows
    #define maxcol 6    //maximum number of columns
    #define maxdim 2    //maximum number of dimensions
    scpi_channel_value_t array[maxrow * maxcol]; //array which holds values in order (2D)
    size_t chanlst_idx; //index for channel list
    size_t arr_idx;     //index for array
    size_t n, m = 1;        //counters for row (n) and columns (m)

    // get channel list
    if ( SCPI_Parameter ( context, &channel_list_param, TRUE ) ) {
        scpi_expr_result_t res;
        scpi_bool_t is_range;
        int32_t values_from[maxdim];
        int32_t values_to[maxdim];
        size_t dimensions;

        bool for_stop_row = false;      //true if iteration for rows has to stop
        bool for_stop_col =false;       //true if iteration for columns has to stop
        int32_t dir_row = 1;            //direction of counter for rows, +/-1
        int32_t dir_col = 1;            //direction of counter for columns, +/-1

        // the next statement is valid usage and it gets only real number of dimensions for the first item (index 0)
        if(!SCPI_ExprChannelListEntry ( context, &channel_list_param, 0, &is_range, NULL, NULL, 0, &dimensions )) {
            chanlst_idx = 0;    //call first index
            arr_idx = 0;        //set arr_idx to 0
            do {        //if valid, iterate over channel_list_param index while res == valid (do-while cause we have to do it once)
                res = SCPI_ExprChannelListEntry ( context, &channel_list_param, chanlst_idx, &is_range, values_from, values_to, 4, &dimensions );
                if (is_range == false) {        //still can have multiple dimensions
                    if (dimensions == 1) {
                        //here we have our values
                        //row == values_from[0]
                        //col == 0 (fixed number)
                        //call a function or something
                        array[arr_idx].row = values_from[0];
                        array[arr_idx].col = 0;
                    } else if (dimensions == 2) {
                        //here we have our values
                        //row == values_fom[0]
                        //col == values_from[1]
                        //call a function or something
                        array[arr_idx].row = values_from[0];
                        array[arr_idx].col = values_from[1];
                    } else {
                        return SCPI_RES_ERR;
                        break;
                    }
                    arr_idx++; //inkrement array where we want to save our values to, not neccessary otherwise
                } else if (is_range == true) {        
                    if (values_from[0] > values_to[0]) {
                        dir_row = -1;   //we have to decrement from values_from
                    } else  { //if (values_from[0] < values_to[0])
                        dir_row = +1;   //default, we increment from values_from
                    } 

                   //iterating over rows, do it once -> set for_stop_row = false
                   //needed if there is channel list index isn't at end yet
                   for_stop_row = false; 
                    for (n = values_from[0]; for_stop_row == false; n +=dir_row) {
                        //usual case for ranges, 2 dimensions
                        if (dimensions == 2) {
                            if (values_from[1] > values_to[1]) {
                                dir_col = -1;
                            } else if (values_from[1] < values_to[1]) {
                                dir_col = +1;
                            }
                            //iterating over columns, do it at least once -> set for_stop_col = false
                            //needed if there is channel list index isn't at end yet
                            for_stop_col = false;
                            for (m = values_from[1]; for_stop_col == false; m +=dir_col) {
                                //here we have our values
                                //row == n
                                //col == m
                                //call a function or something
                                array[arr_idx].row = n;
                                array[arr_idx].col = m;
                                arr_idx++;
                                if (m == values_to[1]) {
                                    //endpoint reached, stop column for-loop
                                    for_stop_col = true;
                                }
                            }
                            //special case for range, example: (@2!1)
                        } else if (dimensions == 1) {
                            //here we have values
                            //row == n
                            //col == 0 (fixed number)
                            //call function or sth.
                            array[arr_idx].row = n;
                            array[arr_idx].col = 0;
                            arr_idx++;
                        }
                        if (n == values_to[0]){
                            //endpoint reached, stop row for-loop
                            for_stop_row = true;
                        }
                    }


                } else {
                    return SCPI_RES_ERR;
                    break;
                }
                //increase index
                chanlst_idx++;
            } while ( SCPI_EXPR_OK == SCPI_ExprChannelListEntry ( context, &channel_list_param, chanlst_idx, &is_range, values_from, values_to, 4, &dimensions ) ) ;
            //while checks, whether incremented index is valid
        }
        //do something at the end if needed
        array[arr_idx].row = 0;
        array[arr_idx].col = 0;
    }
    return SCPI_RES_OK;
}

[j123b567]

Nice example. I will integrate this to documentation and to examples.

Maybe, there can be some helper function for 1 dimension and 2 timensions to do this for you.