ISSUE with 11.4.14 Streaming operators (pack/unpack) if the size of source not even

[karandeep963]

Hello All,

module top;


initial begin
bit data_source [];
byte unsigned pack_data[];

data_source = new[3];
pack_data = new[2];

for(int i = 0 ; i < (data_source.size()) ; i++)begin
    if ((i %2) == 0)data_source[i] = 1'b1;
    $display("INITIALIZED VALUE OF DATA SOURCE [%d] = 0x%x",i,data_source[i]);
end

foreach(pack_data[i])$display("\nUNINITIALIZED VALUE OF PACKED ARRAY[%d] = 0x%x",i,pack_data[i]);

// Casting Little endianess
pack_data = {<<{data_source}};
foreach(pack_data[i])$display("\nVALUE OF {LITTLE ENDIAN} PACKED ARRAY[%d] = 0x%x",i,pack_data[i]);

// Casting BIG endianess
pack_data = {>>{data_source}};
foreach(pack_data[i])$display("\nVALUE OF {BIG ENDIAN} PACKED ARRAY[%d] = 0x%x",i,pack_data[i]);

end

endmodule:top

generates the following results:

 

Both the little endian and big endian results same ???

INITIALIZED VALUE OF DATA SOURCE [          0] = 0x1
INITIALIZED VALUE OF DATA SOURCE [          1] = 0x0
INITIALIZED VALUE OF DATA SOURCE [          2] = 0x1

UNINITIALIZED VALUE OF PACKED ARRAY[          0] = 0x00
UNINITIALIZED VALUE OF PACKED ARRAY[          1] = 0x00

VALUE OF {LITTLE ENDIAN} PACKED ARRAY[          0] = 0xa0

VALUE OF {BIG ENDIAN} PACKED ARRAY[          0] = 0xa0

but if keeping data_source = new[any even number]; // lets say keeping it 4

 

the following results looks fine 

VALUE OF {LITTLE ENDIAN} PACKED ARRAY[          0] = 0x50

VALUE OF {BIG ENDIAN} PACKED ARRAY[          0] = 0xa0

Can anybody help me with this ??

 

Thanks ,

KS

[tudor.timi]

A suggestion for this type of questions: use StackOverflow. There is already a category for SystemVerilog and the you're more likely to get a quick answer.

[tudor.timi]

Also, I remember reading some blog posts on the topic:

 

http://bryan-murdock.blogspot.de/2014/10/systemverilog-streaming-operator.html

http://bryan-murdock.blogspot.de/2014/10/more-systemverilog-streaming-examples.html

 

Have a look at these and see if you can figure out what's happening.

[apfitch]

I think the key sentence is

 

"If the target represents a dynamically sized variable, such as a
queue or dynamic array, the variable is resized to accommodate the entire stream. If, after resizing, the
variable is larger than the stream, the stream is left-aligned and zero-filled on the right."

 

So in your first case, the resulting stream is 101 (length 3) whether you stream it >> or <<. You then assign it to a dynamic array of byte. You therefore end up with

10100000

in a dynamic array is size 1.

 

In the case of data source 4, you start with the pattern

data_source [0] = 1, data_source[1] = 0, data_source[2] = 1, data_source [3] = 0

 

When you stream that with << or >> you get two four bit values, either

 

0101 or

1010

 

When you assign these to the dynamic array you get either

 

01010000

10100000

 

Q.E.D

 

regards

Alan

[karandeep963]

Many Thanks TUDOR and ALAN,

 

That helps a lot. 

 

Thanks to Bryan's Posts as well. 

 

Indeed the tricks needed to use it !!