MATLAB DESIGN HDL CODER RELEASE NOTES User's Guide download pdf (Page 363)

System Generator for DSP User Guide www.xilinx.com 363

UG640 (v 12.2) July 23, 2010

Black Box Examples

4. The black box is able to adjust to changes in input width because of its configuration

M-function. To make this work, the M-function must be augmented by hand. Open the

M-function file transpose_fir_parametric.m. The important points are described

below.

• Obtaining data input width:

input_bitwidth = this_block.port('din').width;

• Calculating output width:

output_bitwidth = ceil(log2(2^(input_bitwidth-1)*2^(coef_bitwidth-1) *

number_of_coef));

• Setting output data type:

dout_port.makeSigned;

dout_port.width = output_bitwidth;

dout_port.binpt = 12;

• Passing input and output bit widths to VHDL as generics:

this_block.addGeneric('input_bitwidth',this_block.port('din').width);

this_block.addGeneric('output_bitwidth',output_bitwidth);

For details concerning the black box configuration M-function, seethe topic Black Box

Configuration M-Function.

If you examine the black box VHDL file transpose_fir_parametric.vhd you see generics

input_bitwidth and output_bitwidth that specify input and output width. These

are passed to lower-level VHDL components.

Simulating Several Black Boxes Simultaneously

Several System Generator black boxes can co-simulate simultaneously, using only one

ModelSim license while doing so. The example shown below illustrates this. The files for

the example are contained in the directory

<ISE_Design_Suite_tree>/sysgen/examples/black_box/example2.

The files contained in this directory are:

• black_box_ex2.mdl: A Simulink model containing two black boxes.

• parity_block.vhd: VHDL for a simple state machine that tracks the running

parity of an 8-bit input word.

• parity_block_config.m: The configuration M-function for the black boxes. The

code has barely been changed from what was produced by the Configuration Wizard:

the line that tagged the block as having a combinational feed-through path

(this_block.tagAsCombinational) has been removed.

Black Box Tutorial Example 6: Simulating Several Black Boxes

Simultaneously

Navigate into the example2 directory and open the example model. This is a simple

model with two identical black boxes, each implementing a state machine. The state

machines compute the running parity of their inputs. One black box is fed the input stream

of the model and the other is fed the input stream after it has been serialized and de-

serialized. Notice that no simulation model is provided for either state machine. Instead,

HDL co-simulation is used to produce simulation results. The ModelSim block provides

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