uvm_packer

The uvm_packer class provides a policy object for packing and unpacking uvm_objects. The policies determine how packing and unpacking should be done. Packing an object causes the object to be placed into a bit (byte or int) array. If the `uvm_field_* macro are used to implement pack and unpack, by default no metadata information is stored for the packing of dynamic objects (strings, arrays, class objects).

Summary

uvm_packer
The uvm_packer class provides a policy object for packing and unpacking uvm_objects.
Packing
pack_field	Packs an integral value (less than or equal to 4096 bits) into the packed array.
pack_field_int	Packs the integral value (less than or equal to 64 bits) into the pack array.
pack_string	Packs a string value into the pack array.
pack_time	Packs a time value as 64 bits into the pack array.
pack_real	Packs a real value as 64 bits into the pack array.
pack_object	Packs an object value into the pack array.
Unpacking
is_null	This method is used during unpack operations to peek at the next 4-bit chunk of the pack data and determine if it is 0.
unpack_field_int	Unpacks bits from the pack array and returns the bit-stream that was unpacked.
unpack_field	Unpacks bits from the pack array and returns the bit-stream that was unpacked.
unpack_string	Unpacks a string.
unpack_time	Unpacks the next 64 bits of the pack array and places them into a time variable.
unpack_real	Unpacks the next 64 bits of the pack array and places them into a real variable.
unpack_object	Unpacks an object and stores the result into value.
get_packed_size	Returns the number of bits that were packed.
Variables
physical	This bit provides a filtering mechanism for fields.
abstract	This bit provides a filtering mechanism for fields.
use_metadata	This flag indicates whether to encode metadata when packing dynamic data, or to decode metadata when unpacking.
big_endian	This bit determines the order that integral data is packed (using pack_field, pack_field_int, pack_time, or pack_real) and how the data is unpacked from the pack array (using unpack_field, unpack_field_int, unpack_time, or unpack_real).

Packing

pack_field

virtual function void pack_field ( uvm_bitstream_t value,
int size )

Packs an integral value (less than or equal to 4096 bits) into the packed array. size is the number of bits of value to pack.

pack_field_int

virtual function void pack_field_int ( logic[63:0] value,
int size )

Packs the integral value (less than or equal to 64 bits) into the pack array. The size is the number of bits to pack, usually obtained by $bits. This optimized version of pack_field is useful for sizes up to 64 bits.

pack_string

virtual function void pack_string ( string value )

Packs a string value into the pack array.

When the metadata flag is set, the packed string is terminated by a null character to mark the end of the string.

This is useful for mixed language communication where unpacking may occur outside of SystemVerilog UVM.

pack_time

virtual function void pack_time ( time value )

Packs a time value as 64 bits into the pack array.

pack_real

virtual function void pack_real ( real value )

Packs a real value as 64 bits into the pack array.

The real value is converted to a 6-bit scalar value using the function $real2bits before it is packed into the array.

pack_object

virtual function void pack_object ( uvm_object value )

Packs an object value into the pack array.

A 4-bit header is inserted ahead of the string to indicate the number of bits that was packed. If a null object was packed, then this header will be 0.

This is useful for mixed-language communication where unpacking may occur outside of SystemVerilog UVM.

Unpacking

is_null

virtual function bit is_null ()

This method is used during unpack operations to peek at the next 4-bit chunk of the pack data and determine if it is 0.

If the next four bits are all 0, then the return value is a 1; otherwise it is 0.

This is useful when unpacking objects, to decide whether a new object needs to be allocated or not.

unpack_field_int

virtual function logic[63:0] unpack_field_int ( int size )

Unpacks bits from the pack array and returns the bit-stream that was unpacked.

size is the number of bits to unpack; the maximum is 64 bits. This is a more efficient variant than unpack_field when unpacking into smaller vectors.

unpack_field

virtual function uvm_bitstream_t unpack_field ( int size )

Unpacks bits from the pack array and returns the bit-stream that was unpacked. size is the number of bits to unpack; the maximum is 4096 bits.

unpack_string

virtual function string unpack_string ( int num_chars = -1 )

Unpacks a string.

num_chars bytes are unpacked into a string. If num_chars is -1 then unpacking stops on at the first null character that is encountered.

unpack_time

virtual function time unpack_time ()

Unpacks the next 64 bits of the pack array and places them into a time variable.

unpack_real

virtual function real unpack_real ()

Unpacks the next 64 bits of the pack array and places them into a real variable.

The 64 bits of packed data are converted to a real using the $bits2real system function.

unpack_object

virtual function void unpack_object ( uvm_object value )

Unpacks an object and stores the result into value.

value must be an allocated object that has enough space for the data being unpacked. The first four bits of packed data are used to determine if a null object was packed into the array.

The is_null function can be used to peek at the next four bits in the pack array before calling this method.

get_packed_size

virtual function int get_packed_size()

Returns the number of bits that were packed.

Variables

physical

bit physical = 1

This bit provides a filtering mechanism for fields.

The abstract and physical settings allow an object to distinguish between two different classes of fields. It is up to you, in the uvm_object::do_pack and uvm_object::do_unpack methods, to test the setting of this field if you want to use it as a filter.

abstract

bit abstract

This bit provides a filtering mechanism for fields.

The abstract and physical settings allow an object to distinguish between two different classes of fields. It is up to you, in the uvm_object::do_pack and uvm_object::do_unpack routines, to test the setting of this field if you want to use it as a filter.

use_metadata

bit use_metadata

This flag indicates whether to encode metadata when packing dynamic data, or to decode metadata when unpacking. Implementations of uvm_object::do_pack and uvm_object::do_unpack should regard this bit when performing their respective operation. When set, metadata should be encoded as follows:

For strings, pack an additional null byte after the string is packed.
For objects, pack 4 bits prior to packing the object itself. Use 4’b0000 to indicate the object being packed is null, otherwise pack 4’b0001 (the remaining 3 bits are reserved).
For queues, dynamic arrays, and associative arrays, pack 32 bits indicating the size of the array prior to to packing individual elements.

big_endian

bit big_endian = 1

This bit determines the order that integral data is packed (using pack_field, pack_field_int, pack_time, or pack_real) and how the data is unpacked from the pack array (using unpack_field, unpack_field_int, unpack_time, or unpack_real). When the bit is set, data is associated msb to lsb; otherwise, it is associated lsb to msb.

The following code illustrates how data can be associated msb to lsb and lsb to msb:

class mydata extends uvm_object;

  logic[15:0] value = 'h1234;

  function void do_pack (uvm_packer packer);
    packer.pack_field_int(value, 16);
  endfunction

  function void do_unpack (uvm_packer packer);
    value = packer.unpack_field_int(16);
  endfunction
endclass

mydata d = new;
bit bits[];

initial begin
  d.pack(bits);  // 'b0001001000110100
  uvm_default_packer.big_endian = 0;
  d.pack(bits);  // 'b0010110001001000
end