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Garbage on Screen with VGA_textmode
01-04-2016, 07:40 PM (This post was last modified: 01-04-2016 08:28 PM by Claude.)
Post: #1
Garbage on Screen with VGA_textmode

I have a problem with the VGA_textmode module in F32C.
The display outputs only garbage characters , afaik at least in the Bootloader the output should show "FleaFPGA-Uno f32c: 50MHz MIPS-compatible soft-core, 512KB SRAM". But even in the Bootloader is only garbage on the screen

[Image: garbage.jpg]

I tried both and Xarx's F32C branch. Both with the same behaviour. I used the project ldf files supplied from the git trees, regenerated the pll and ddr ipx modules.

The CPU seems to run fine , at least I can upload the f32c_consoletest programm with the Arduino IDE and I get proper serial output
No Keyboard

Any hints what could be wrong?
I'm using Lattice Diamond 64bit on a 64bit Win7 machine.

Using the premade F32C bitstream from the site everything works without a flaw Undecided


Going back to 2f7075f6182254b6cd76312c6fcfa93e6b6d5d70 from and i get a working F32C system.
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01-05-2016, 12:09 PM
Post: #2
RE: Garbage on Screen with VGA_textmode
Hello Claude,

Thanks for your question.

I have chatted with one of the F32c project maintainers (Xark) and he provided an explanation of your problem..

What you are seeing is perfectly normal for the latest F32c build. Reason why you are seeing random garbage on-screen, is because the latest F32c SoC (system on chip) design now includes an option to use external SRAM (which is now default setting) to store text, not just BRAM as per the earlier controller..

If you desire to see the boot screen, in FleaFPGA_Uno_RevisionE_toplevel.vhd you can change the following attributes :

C_vgatext_text_fifo to := false
C_mem_size := 2 to (at least 4).

Due to upgrades to the F32c video controller your test sketches may also not be up to date. I would suggest you download and try the latest test sketches from the "f32c/Arduino" top-level tree from github. Thanks again!

Hope this helps Smile

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01-05-2016, 12:39 PM
Post: #3
RE: Garbage on Screen with VGA_textmode

Yeah, there are so many "generic parameters" it is hard to keep them all straight. I totally need to write up a bit more about the VGA_textmode ones.

However, as configured by default as Valentin mentions it is using 8KB of BRAM just for font data, and has a text screen and 16-color bitmap coming from SRAM.

If you try the File|Examples|f32c_VGATextConsole|f32c_VGAConsoleFeatures you should see the screen cleared (at least for a bit before it on purpose puts some "garbage" there to demo scrolling).

For a slightly better example, I have just updated f32c_VGATextConsole library with another example called "f32c_16ColorBMapTest".

[Image: SnrTJ5R.jpg]

Sorry about the lack of documentation (and a "moving target"). The f32c_VGATextConsole library does have a fairly complete set of "helper functions" to use the VGA at run time (and detect its configuration).

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01-11-2016, 09:39 PM
Post: #4
RE: Garbage on Screen with VGA_textmode

thanks for the answers and clarification. I update my Arduino and F32C trees then Smile
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