Testbench for verification of digital logic

Testcase Description

This Testcase is to check the Goldcode generation and creating Half chip delays incase of No acquisition. The Carrier Frequency has been set to 0Hz and the Cosine wave has an amplitude of +1 and Sine wave has an amplitude of 0 throughout the simulation time. The Input Goldcode Text file contains a delayed version of the goldcode data corresponding to Satellite 20. This data has been created using Matlab and fed into the RTL. With Delay we have introduced, an acquistion peak value of around 5000 is expected around 6ms time. This can be checked by viewing the waveform gps_engine_i.ch1.tid.dip_track , gps_engine_i.ch1.tid.die_track , gps_engine_i.ch1.tid.dil_track. From the waveform, we can interpret that the Half a chip delay introduction increases the I arm data and thus acquistion peak is reached. After reaching peak, as we have given the Threshold value to be high for demonstrational purposes, the Delay chipping continues and the peak is not seen in the subsequent epochs.

The design files reside in GPS_Baseband/verilog/rtl/gps_engine and are listed below.

1. accumulator.v - 20 bit accumulator
2. adc2to3bit.v - Two to three bit mapping of the input data
3. clk_gen_gps_new.v - Module containing NCO for Carrier Generation and code clock generation
4. codectrllogic.v- Topmost module for generation of three versions of Goldcodes (Early,Late,Prompt)
5. codegen.v - Goldcode instantiation module
6. goldcode.v- Goldcode generation module based on the Satellite ID
7. gps_multichannel.v - Topmost Module containing 8 single channels and address decoding
8. gps_single_channel.v - Single channel module containing all module instantiations and Wishbone Interface
9. signmag_twocomp_vv.v - Sign Magnitude to Two's complement Conversion
10. signmul.v - 3 bit Sign Magnitude Number multiplier
11. thresh_control.v - Threshold check block to generate Carrier change pulse to invoke Doppler
12. threshold.v - Threshold check block to check whether the satellite is acquired or not
13. track_intganddump.v - Gold code multiplication with Integrate and dumping of 6 signals(3 - i and 3 - q)
14. wb_interface.v - Wishbone Interface containing Registers and flag declarations

Further explanation on the operation given in.

Requirements

The testbench given here requires two programs.

1. Icarus Iverilog - Please take a look at iverilog's github repository (link given above) for installation instructions.

2. GTKWave Analyser - GTKWave can be installed easily on Ubuntu using apt, the package manager.

sudo apt-get install gtkwave

Once these programs are installed, you can open your terminal in this folder (/verilog/dv/wb_bfm_goldcode_test) and run the following commands.

chmod +x verify_gold.sh
./verify_gold.sh

In the window opened by GTKWave, please click on gps_engine_tb that appears on the left pane. It will list internal instantiations. Go through the hierarchy and select any signal which you want to view and click insert which will be present at the bottom.

Go Inside gps_engine_i --> ch1 --> tid --> Click on it to list the waveforms in that module --> Click on dip_track,die_track,dil_track and give insert --> You will be able to see a drastic increase in the accumulated value around 6ms which shows us that the Gold code generation is done correctly.