Novatron

Using, learning, programming and modding the Gigatron and anything related.
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lb3361
Posts: 205
Joined: 17 Feb 2021, 23:07

Re: Novatron

Post by lb3361 »

The code that tests whether there is a sd card is found in Reset.gcl. It does the things that tiens the card into spi mode, tries the reset command, and checks whether the card answers...
alastair
Posts: 63
Joined: 10 Oct 2019, 14:28

Re: Novatron

Post by alastair »

I haven't had a chance to work on the SD card since the last update. The Famicom controllers finally showed up, so I was testing those. I found a listing of the original controllers that were shipped with the Gigatron and ordered a few. What was shipping turned out to be different though and initially I couldn't get them to work at all.

Then I realized I had wired up the power on the connector the wrong way round :roll: So after blowing up a few I was finally able to get the controller to do something. The buttons on these controllers are all mapped differently. I seem to have all the controls, so I should be able to fix that in software.

There is an issue when both the controller and ATtiny85 are connected. I can add a pair of diodes with one connected to each of the data inputs. The existing resistor will pull the input high and then get pulled low if either of the inputs go low via the diode.

Code: Select all

      Vcc
       |
      [R]  +--|>|-- Famicom
       |   |
input--+---+--|>|-- ATtiny85

bmwtcu
Posts: 132
Joined: 01 Nov 2018, 12:02

Re: Novatron

Post by bmwtcu »

The buttons on these controllers are all mapped differently.
What's the mapping you see with these?
alastair
Posts: 63
Joined: 10 Oct 2019, 14:28

Re: Novatron

Post by alastair »

I don't think I have a button that maps to "start". This is how the rest map.

Code: Select all


      [ up ]                                [right]
[down]      [left]                    [A/B?]      [right]
      [ ?? ]        [  ??  ][select]        [A/B?]
      
Attachments
Screen Shot 2022-08-18 at 11.04.09 AM.png
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bmwtcu
Posts: 132
Joined: 01 Nov 2018, 12:02

Re: Novatron

Post by bmwtcu »

Are you sure that UP is mapped that way? If your UP button is mapped to START, I may have an explanation for what you're seeing.

I would expect that you're seeing:-

Code: Select all


    [ start ]                            [right]
[down]      [left]                    [A]      [right]
      [ up ]        [  B  ][select]        [A]

If the controller is shifting on a different PULSE clock edge direction from what the 595 on the Gigatron expects, it could transpose the bits as shown below. (2nd column is what Gigatron expects, 3rd column shows bits transposed by 1)

Code: Select all

BIT7    buttonA            buttonRight  
BIT6    buttonB            buttonA
BIT5    buttonSelect       buttonB      
BIT4    buttonStart        buttonSelect 
BIT3    buttonUp           buttonStart  
BIT2    buttonDown         buttonUp     
BIT1    buttonLeft         buttonDown   
BIT0    buttonRight        buttonLeft   
Can you share a waveform of PULSE/LATCH/DATA at the 595 while pressing START?
alastair
Posts: 63
Joined: 10 Oct 2019, 14:28

Re: Novatron

Post by alastair »

bmwtcu wrote: 18 Aug 2022, 15:19 I would expect that you're seeing:-

Code: Select all


    [ start ]                            [right]
[down]      [left]                    [A]      [right]
      [ up ]        [  B  ][select]        [A]
Yes, you are correct. I had the up and start mixed up. Holding the top button triggers the reset, so that would be the start button.
bmwtcu wrote: 18 Aug 2022, 15:19 Can you share a waveform of PULSE/LATCH/DATA at the 595 while pressing START?
I'll set up the oscilloscope and post some screenshots. Thanks for the insight!
bmwtcu
Posts: 132
Joined: 01 Nov 2018, 12:02

Re: Novatron

Post by bmwtcu »

Not sure if Rev 1.3 is a downrev schematic, but HSYNC_B shouldn't be wired up to the 595 twice on pins 11 and 12. I assume you already addressed that.
alastair
Posts: 63
Joined: 10 Oct 2019, 14:28

Re: Novatron

Post by alastair »

I label "OUT6" as ~HSYNC in my schematic. This looks correct. I see pins 11 and 12 of the 595 connected to OUT6 on the Gigatron PCB.
bmwtcu
Posts: 132
Joined: 01 Nov 2018, 12:02

Re: Novatron

Post by bmwtcu »

DOH, my bad. I was expecting to see LATCH and forgot that it feeds the DB9 pin directly.
alastair
Posts: 63
Joined: 10 Oct 2019, 14:28

Re: Novatron

Post by alastair »

I think the controller issue may be a timing glitch. I was testing things out and see the bits getting transposed when plugged into a VGA monitor. I plugged in a VGA-to-HDMI adapter and issue goes away. The controller buttons are all mapped correctly, so the data is getting latched as expected.

This might be caused by a reflection coming from the VGA cable because the impedance isn't matched to the 75 ohms of the monitor. That could delay the LATCH or advance the PULSE causing it to miss the first bit. I'll need to think it through to figure out where the problem is.

I remember seeing something from Marcel related to this and tracked it down here - https://cdn.hackaday.io/files/207818890 ... %20R17.pdf

Note: I don't have this 68-ohm resistor in my current design.
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