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Reset Settings and Parameters

This page describes parameters in the Clock Settings section of the HDL Code Generation > Global Settings pane of the Configuration Parameters dialog box. Using these parameters, you can specify the reset name, whether to use a synchronous or asynchronous reset, and whether the reset is asserted active-high or active-low.

Reset type

Specify whether to use asynchronous or synchronous reset logic when generating HDL code for registers. It is recommended that you specify the Reset type as Synchronous when you use a Xilinx® device and Asynchronous when you use an Altera® device.

Settings

Default: Asynchronous

Asynchronous

Use asynchronous reset logic. This reset logic samples the reset independent of the clock signal.

The following process block, generated by a Unit Delay block, illustrates the use of asynchronous resets. When the reset signal is asserted, the process block performs a reset, without checking for a clock event.

Unit_Delay1_process : PROCESS (clk, reset)
  BEGIN
    IF reset = '1' THEN
      Unit_Delay1_out1 <= (OTHERS => '0');
    ELSIF clk'event AND clk = '1' THEN
      IF clk_enable = '1' THEN
        Unit_Delay1_out1 <= signed(x_in);
      END IF;
    END IF; 
  END PROCESS Unit_Delay1_process;

Synchronous

Use synchronous reset logic. This reset logic samples the reset with respect to the clock signal.

The following process block, generated by a Unit Delay block, checks for a clock event, the rising edge, before performing a reset:

Unit_Delay1_process : PROCESS (clk)
  BEGIN
    IF rising_edge(clk) THEN
      IF reset = '1' THEN
        Unit_Delay1_out1 <= (OTHERS => '0');
      ELSIF clk_enable = '1' THEN
        Unit_Delay1_out1 <= signed(x_in);
      END IF;
    END IF; 
  END PROCESS Unit_Delay1_process;

Command-Line Information

Property: ResetType
Type: character vector
Value: 'async' | 'sync'
Default: 'async'

To set this property, use hdlset_param or makehdl. To view the property value, use hdlget_param.

For example, you can specify sync as the ResetType when you generate HDL code for the symmetric_fir subsystem inside the sfir_fixed model using either of these methods.

  • Pass the property as an argument to the makehdl function.

    makehdl('sfir_fixed/symmetric_fir', ... 
            'ResetType','async')
  • When you use hdlset_param, you can set the parameter on the model and then generate HDL code using makehdl.

    hdlset_param('sfir_fixed','ResetType','async')
    makehdl('sfir_fixed/symmetric_fir')

See Also

Reset asserted level

Specify whether the asserted or active level of the reset input signal is active-high or active-low.

Settings

Default: Active-high

Active-high

Specify that the asserted level of reset input signal is active-high. For example, the following code fragment checks whether reset is active high before populating the delay_pipeline register:

Delay_Pipeline_Process : PROCESS (clk, reset)
BEGIN
  IF reset = '1' THEN
    delay_pipeline(0 TO 50) <= (OTHERS => (OTHERS => '0'));
.
.
.

Active-low

Specify that the asserted level of reset input signal is active-low. For example, the following code fragment checks whether reset is active low before populating the delay_pipeline register:

Delay_Pipeline_Process : PROCESS (clk, reset)
BEGIN
  IF reset = '0' THEN
    delay_pipeline(0 TO 50) <= (OTHERS => (OTHERS => '0'));
.
.
.

Dependency

If you input a logic high value to the Reset input port, to reset the registers in your design, set Reset asserted level to Active-high. if you input a logic low value to the Reset input port, to reset the registers in your design, set Reset asserted level to Active-low.

Command-Line Information

Property: ResetAssertedLevel
Type: character vector
Value: 'active-high' | 'active-low'
Default: 'active-high'

To set this property, use hdlset_param or makehdl. To view the property value, use hdlget_param.

For example, you can specify this property while generating HDL code for the symmetric_fir subsystem inside the sfir_fixed model using either of these methods.

  • Use hdlset_param to set the parameter on the model. Then generate HDL code using makehdl.

    hdlset_param('sfir_fixed','ResetAssertedLevel','active-high')
    makehdl('sfir_fixed/symmetric_fir')

  • Pass the property as an argument to the makehdl function.

    makehdl('sfir_fixed/symmetric_fir','ResetAssertedLevel','active-high')

See Also

Reset input port

Enter the name for the reset input port in generated HDL code.

Settings

Default: reset

Enter a character vector for the reset input port name in generated HDL code.

For example, if you override the default with 'chip_reset' for the generating system myfilter, the generated entity declaration might look as follows:

ENTITY myfilter IS
   PORT( clk             :  IN  std_logic;
         clk_enable      :  IN  std_logic;
         chip_reset      :  IN  std_logic;
         myfilter_in     :  IN  std_logic_vector (15 DOWNTO 0); 
         myfilter_out    :  OUT std_logic_vector (15 DOWNTO 0); 
         );
END myfilter;

If you specify a VHDL® or Verilog® reserved word, the code generator appends a reserved word postfix string to form a valid VHDL or Verilog identifier. For example, if you specify the reserved word signal, the resulting name string would be signal_rsvd.

Dependency

If you specify active-high for Reset asserted level, the reset input signal is asserted active-high. To reset the registers in the entity, the input value to the Reset input port must be high. If you specify active-low for Reset asserted level, the reset input signal is asserted active-low. To reset the registers in the entity, the input value to the Reset input port must be low.

Command-Line Information

Property: ResetInputPort
Type: character vector
Value: A valid identifier in the target language
Default: 'reset'

To set this property, use hdlset_param or makehdl. To view the property value, use hdlget_param.

For example, you can specify sync as the ResetType when you generate HDL code for the symmetric_fir subsystem inside the sfir_fixed model using either of these methods.

  • Pass the property as an argument to the makehdl function.

    makehdl('sfir_fixed/symmetric_fir', ... 
            'ResetInputPort','rstx')
  • When you use hdlset_param, you can set the parameter on the model and then generate HDL code using makehdl.

    hdlset_param('sfir_fixed','ResetInputPort','rstx')
    makehdl('sfir_fixed/symmetric_fir')

See Also