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Data Types

Data Types. Composite Date Types. Arrays Single and multi-dimensional Arrays are single Type Records Records are mixed types. Array. Array is an Indexed Collection of Elements All of the Same Type One-dimensional with one index Multi-dimensional with several indices .

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Data Types

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  1. Data Types

  2. Composite Date Types • Arrays • Single and multi-dimensional • Arrays are single Type • Records • Records are mixed types

  3. Array • Array is an Indexed Collection of ElementsAll of the Same Type • One-dimensional with one index • Multi-dimensional with several indices

  4. Constrained versus unconstrained Arrays • Constrained • the bounds for an index are established when the type is defined • Unconstrained • the bounds are established after the type is defined • Each position in the array has a scalar index value associated with it

  5. Array Definition Syntax and Example array( discrete_range{,... }) ofelement_subtype_indication; discrete_range is an index • name of previously declared type with optional range constraint type Large_Word isarray ( 63 downto 0 ) ofbit ; type Address_List is array ( 0 to 7 ) ofLarge_Word ; Example 1 Example 2

  6. More examples of Array Declaration array( discrete_range{,... }) ofelement_subtype_indication; type 2D_FFT is array ( 1 to 128, 1 to 128 ) of real ; type Scanner is array ( byte range 0 to 63 ) of integer ; type Sensor_Status is array ( Stdby, On, Off ) of time ;

  7. Unconstrained Declaration of array type Detector_Array is array ( natural range <> ) of natural ; • The symbol ‘<>’ is called a box and can be thought of as a place-holderfor the index range. • Box is filled in later when the type is used. variable X_Ray_Detector :Detector_Array ( 1 to 64 ) ;

  8. Two Examples of Predefined Unconstrained Types type string is array ( positive range <> ) ofcharacter ; type bit_vector is array ( natural range <> ) of bit ;

  9. Two more Examples of Predefined Unconstrained Types type std_ulogic_vector is array ( natural range <> ) of std_ulogic ; type bit_vector is array ( natural range <> ) of bit ;

  10. Unconstrained Array Ports • 1. Specify Port as unconstrained • 2. Determine size of port by Index Bounds of Signal • e.g., AND Gates With Different Number of Inputs You do the following:

  11. 1. Example of entity of Unconstrained Array Port y i And_Multiple You specify vector of bits with no number here entity And_Multipleis port ( i :in bit_vector ; y :out bit ) ; end entity And_Multiple ;

  12. 2. AND, example continued y i architecture And_Multiple_B of And_Multiple is begin And_Reducer : process ( i) is variable Result:bit ; begin Result := ‘1’ ; for Index in i’Rangeloop Result := Result and i ( Index ); end loop ; You use Range so you still do not tell how many bits variable Signal created outside the loop

  13. AND, example continued y <= Result ; end process And_Reducer; end architecture And_Multiple_B ; signal Here we finished architecture And_Multiple_B without specifying number of bits In the next slide we will call this architecture structurally and at this time the number of bits will be decided

  14. AND, e.g., y i And_Multiple count_value 8 bits terminal_count signal count_value : bit_vector ( 7 downto 0 ) ; signal terminal_count :bit ; tc_gate :entity work.And_Multiple ( And_Multiple_B ) port map ( i => count_value , y => terminal_count ); architecture And_Multiple_B • The Input Port Is Constrained by the Index Range of the Input Signal, i.e., An 8-Input AND Gate.

  15. Array References • Arrays Can Be Equated, Rather Than Having to Transfer Element by Element • Refer to Individual Elements By: • 1. Single Index Value, e.g., A ( 5 ) • 2. Range: a contiguous sequence of a one-dimensional array can be referred to by using it as an index. e.g., A( 5 to 15 ) • 3. Previously defined subtype • 4. Index types do not have to be the same

  16. Examples of Array Aggregate Sensor_Status type Sensor_Status is array ( Stdby ,On ,Off ) of time ; variable FLIR_Status : Sensor_Status := ( 0 sec , 0 sec , 0 sec ); variable FLIR_Status : Sensor_Status := ( On => 5 sec ) ; Stdby On Off Changes only one field

  17. Array Aggregate Syntax • A List of Element Values Enclosed in Parentheses • This list is used to initialize Elements of an Array to Literal Values aggregate <= ([choices=>] expression{ ... }) type Sensor_Status is array ( Stdby ,On ,Off ) of time ; syntax

  18. There are two ways to refer to elements in Array Aggregate • Two Ways of Referring to Elements • Positional: explicitly list values in order • Named Association: Explicitly list values by their index using “choices” • Order NOT important • Positional and Named Association Cannot Be Mixed Within an Aggregate.

  19. Example of Named Association in Array Aggregate • othersCan Be Used in Place of an Index in a Named Association, • Indicating a Value to Be Used for All Elements Not Explicitly Mentioned variable FLIR_Status :Sensor_Status := ( Off => 10 min,others=> 0 sec ) ; • Named Association: Explicitly list values by their index using “choices” • Order NOT important

  20. Example of setting many elements to one value in Array Aggregate • A Set of ValuesCan Be Set to a Single Value by Forming a List of Elements Separated by Vertical Bars, | . type 2D_FFT is array ( 1 to 128, 1 to 128 ) of real ; variable X_Ray_FFT : 2D_FFT := ( ( 60, 68 ) | ( 62, 67 ) | ( 67, 73 ) | ( 60, 60 )=> 1.0 ,others0.0 ); Here I set 4 elements of array to 1 all other to 0

  21. Array Operations: element by element logic operations • One-Dimensional Arrays of Bit or Boolean • Element by element AND, OR, NAND, NOR, XOR, XNOR can be done on array type Large_Word is array ( 63 downto 0 ) of bit ; variable Samp_1 , Samp_2:Large_Word ( 0 to 63 => ‘0’ ) ; Here we declare variables Samp_1 and Samp_2 that we will use next 0 0 Large_Word 63 0

  22. Array Operations: element by element logic operations constant Bit_Mask : Large_Word ( 8 to 15 => ‘1’ ) ; Samp_2 := Samp_1 and Bit_Mask ; Bits from 8 to 15 are AND-ed with Bit_Mask

  23. NOT Operations Array Operations: element by element logic operations • Complement of elements of a single array, NOT Samp_2 := not Samp_1 ;

  24. 1D Shift and Rotate Array Operations • One-Dimensional Arrays Can Be Shifted and Rotated • Shift • Logical: Shifts and fills with zeros • Arithmetic: Shifts and fills with copies from the end being vacated • Rotate • Shifts bits out and back in at other end

  25. Shift and rotate operations Shift left logic B” 1010_1100 ”sll 4 == B” 1100_0000 ” B” 1010_1100 ”sla 4 == B” 1100_0000 ” B”1010_1100 ”sra 4 == B”1111_1010 ” B” 1010_1100 ”rol 4 == B” 1100_1010 ” Shift right arithmetic Rotate left

  26. Relational Array Operations • One-Dimensional Arrays Can Be Operated on by Relational Operators, = , /= , < , <= , > , >= • Arrays need not be of the same length • Arrays must be of same type

  27. Array Operations: Concatenation • Concatenation Operator, & • Can combine array and scalar B” 1010_1100 ”& B” 1100_0000 ” == B” 1010_1100_1100_0000 ” B” 1010_1100 ”& ‘1’ == B” 1010_1100_1 ”

  28. Conversion from one Array Type to another • One Array Type Can Be Converted to Another If: • Same element type • Same number of dimensions • Same index types

  29. Example of Array Type Conversions Example subtype name is string ( 1 to 20 ) ; type display_string is array ( integer range 0 to 19 ) of character ; variable item_name :name ; variable display :display_string ; display:= display_string ( item_name ); 1 to 20 0 to 19

  30. Example of Array Aggregate • Assignments Can Be Made From a Vectorto an Aggregateof Scalars or Vice-Versa. type Sensor_Status is array ( Stdby, On, Off ) of time ; variable Stdby_Time,On_Time, Off_Time :time ; Variable FLIR_Status : Sensor_Status := ( 0 sec , 0 sec , 0 sec ) ; ( Stdby_Time, On_Time, Off_Time ) := Flir_Status ; Aggregate of scalars

  31. Predefined Attributes • Predefined Attributes deal with data obtained from Blocks, Signals, Types and Subtypes • Return values such as: • length of an array type • time since last signal change • range of values in a type • Predefined attributes are useful for performing certain type of functions such as: • timing checks • bounds • clock edge detection • type conversion We showed earlier attributes for signals. Now we show for types

  32. Array Type Bound Example: use of predefined attributes attribute

  33. Another Example of array bound

  34. Multi-range array attributes

  35. Array length attributes

  36. Range attributes

  37. Type attributes position function

  38. Homework: Attributes Exercise

  39. Example of using Attributes We calculate resistance dividing voltage by current

  40. User Defined Attributes • These attributes attach data to objects • They are defined by the user of Data types • Data is constant • They are accessed with the same syntax as predefined attributes

  41. User Defined Attributes

  42. Records • Records in VHDL are collections of Named Elements of Possibly Different Types. • To refer to a Field of a Record Object, you should use a Selected Name.

  43. Example of a Record * type instruction is record op_code :processor_op ; address_mode :mode ; operand1, operand2 : integer range 0 to 15 ; end record ; *Ashenden, VHDL cookbook

  44. Records • Aggregates Can Be Used to Write Literal Values for Records. • Positional and Named Association Can Be Used • Record field names being used in place of array index names.

  45. End of Lecture

  46. Sources Prof. K. J. Hintz Department of Electrical and Computer Engineering George Mason University

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