Bergmann, Andreas

yuce, emrah

Krepa, Michal

Discrete Cosine Transform core

I am trying to run the testbench in this project using NVC (https://github.com/nickg/nvc).

I am using their recommended way to generate the simulation files using the command

`nvc -a MDCT_PKG.vhd MDCTTB_PKG.vhd ROMO.VHD ROME.VHD RAM.VHD CLKGEN.VHD DBUFCTL.VHD DCT1D.vhd DCT2D.VHD MDCT.VHD random1.vhd INPIMAGE.VHD MDCT_TB.VHD -e my_tb -r`

However, upon running this, I get an error which says
```** Error: expected type of range bound to be STD.STANDARD.REAL but is STD.STANDARD.INTEGER
	File MDCTTB_PKG.vhd, Line 47
              of REAL(ROMDATA_W-1 downto 0);```

Any help is greatly appreciated.

Unable to simulate testbench with NVC

This core works very well, I've tested it thoroughly to implement it as part of a JPEG compressor. But there are some things which I consider very important but are missing in the documentation:

1. The core does internally a level_shift (substract 128 from input). I don't think a DCT core should do level shift (i.e. MatLab's dct2 function doesn't). The code in DCT1D.vhd can be modified to avoid it by changing every "SIGNED('0' & dcti) - LEVEL_SHIFT" to "SIGNED(dcti(dcti'High) & dcti)"

2. If you want output to be row-wise, input must be column-wise, that is, output is the transposed 2D-DCT of the input.

3. I am going to try to see if the DCT is compliant with the JPEG standard in terms of calculation precision. To this moment, it looks fine (I've seen rounding errors of around abs(err)<3 in the 12 bit coefficients, not bad).

4. This is said in the docs, but if you were wondering: yes, you can continuously feed data in to the core and get continuous output.

Great job and very readable code. Many thanks to the author!

Important details missing in docs

The "mif" files pointed to in the rome_xil.vhd and romo_xil.vhd files are in this path: "c:/elektronika/dct/mdct/source/xilinx/....", I guess it should be a relative path ;)

By the way, in the Overview you mention this core has an 8 bit input and a 11 bit output, although, as far as I see, the output is 12 bits. Anyways, great job.

Browse

Discrete Cosine Transform core