Newbie advice on making a simple dev cart.

R-T-B · Post by **R-T-B** » Mon Aug 17, 2009 7:11 pm

Jeroen wrote:One note....are you using eproms? Cause you cant program those using copynes (iirc) since they need a special voltage to be programmed.

Could someone confirm/deny this? I may either have to cancel an order, or order an EPROM programmer (I think that latter). Any advice either way? What should I be using if not EPROMs? Would non-volatile SRAM work? Flash? and also, what's a good programmer?

Tormenter · Post by **Tormenter** » Tue Aug 18, 2009 8:10 am

R-T-B wrote:
Jeroen wrote:One note....are you using eproms? Cause you cant program those using copynes (iirc) since they need a special voltage to be programmed.
Could someone confirm/deny this? I may either have to cancel an order, or order an EPROM programmer (I think that latter). Any advice either way? What should I be using if not EPROMs? Would non-volatile SRAM work? Flash? and also, what's a good programmer?

Correct, you cant use a copynes to program them, I would just cancel

R-T-B · Post by **R-T-B** » Tue Aug 18, 2009 1:27 pm

As I thought, it's too late to cancel the EPROM order, so I ordered a simple programmer. Should work fine. I already have the UV Light eraser so it isn't SO bad. I need a programmer anyways.

R-T-B · Post by **R-T-B** » Fri Aug 21, 2009 12:10 pm

Ok, I installed a ZIF Socket for each rom chip and cut a hole in the cart. When I program my EPROMs however (and they are verifying and all that, I'm using Willem PCB5.0), all I get is a grey screen. Any idea why? I'm socketing the roms directly with no pin modifications, and using the 16kb and 8kb roms I listed above in the links. What's the deal? I thought I could wire these directly.

Feel free to call me a dumbass, I'm hardly good at this, lol.

Jeroen · Post by **Jeroen** » Fri Aug 21, 2009 12:15 pm

Are you inserting the roms properly? Did you set the jumpers correctly? It could be that your nbasic programs are just not compatible with a real nes.....(nbasic really isnt that good of a programmer platform)

R-T-B · Post by **R-T-B** » Fri Aug 21, 2009 12:18 pm

I find that hard to believe... See, all it does is scroll a line of text. Seems like it should do something...

And yeah, I'm looking into learning ASM for the 6502. Shouldn't be that hard. This is just a test.

The roms are inserted correctly. with pin one oriented properly like the original chips. These are EPROMs, I imagine they should be pin for pin compatable, no?

Jeroen · Post by **Jeroen** » Fri Aug 21, 2009 12:21 pm

They should be.....that's weird...check for cold joints.

R-T-B · Post by **R-T-B** » Fri Aug 21, 2009 12:30 pm

Got out my multimeter and working on that. Reburning the roms too for good measure with a full 10 minute erasure and blank test.

Jeroen · Post by **Jeroen** » Fri Aug 21, 2009 12:35 pm

Uv eraser right? (I thought you said they were uv eproms) Also....can you post the program here? We could check to.

R-T-B · Post by **R-T-B** » Fri Aug 21, 2009 12:38 pm

Yep, UV light eraser. I'll post the program if this doesn't work, know in 15 minutes. It's really simple.

R-T-B · Post by **R-T-B** » Fri Aug 21, 2009 1:19 pm

It works now. I had the mirroring set wrong for the board.

R-T-B · Post by **R-T-B** » Sat Aug 22, 2009 7:43 pm

I'm going to post the program now. I thought I had it working, but behavior in an emulator and on my devcart are drasticly different. It works fine in an emulator, but just draws a whole bunch of jibberish on a real NES. Try it and you'll see what I mean. It might just be that I used nbasic, but the program seems so simple I don't see how it couldn't work (It literally scrolls a line of text based on an example from Bob Rost's site). The archive attatched contains ines binaries, .asm source, and nbasic source versions. Could someone please point out the obvious to me, as I'm sure it probably is very simple and I am just missing it.

Thanks again all.

http://21gunsoftware.com:8080/PRG.zip

thefox · Post by **thefox** » Sat Aug 22, 2009 8:30 pm

I tried your program in Nintendulator, Nestopia and FCEUX.. seemed pretty glitchy in all of them. Try to make it work in those emus correctly before trying it on devcart.

Couple of things that are obviously wrong:
- You have to wait for couple of frames at the start of the program to let the PPU "warm up" (there should be an example in the NesDev wiki). Also it is good practice to do a bunch of other init stuff, like disabling interrupts etc if you dont need them.
- Your vwait routine seems broken/strange, what is all that counter stuff inside the loop?
- You shouldn't even be using polling for checking for vblank, as you will miss vblanks every now and then with this method. Instead detect vblank using the NMI IRQ.
- All your vectors point to "start", don't do that... instead have those vectors point to an RTS instruction.. again good practice.

There are other oddities/problems too but I'm too tired to list them all...

R-T-B · Post by **R-T-B** » Sat Aug 22, 2009 8:35 pm

Oh man, I forgot entirely about those counters... Haha, thought I had pulled them out. They were meant to slow the scroll speed. Don't worry, I'll start with ripping those out. I'll also get those emulators and see if I can't get more consistent results.

Actually, I was unaware of the wiki here and mostly working by reverse engineering Bob Rosts works. Thanks for the great pointer to that resource.

Thanks a bunch. Just wanted reassurance it wasn't a hardware problem, and it doesn't look to be one. After some reading, I immediately see several things wrong.

thefox · Post by **thefox** » Sat Aug 22, 2009 8:39 pm

If you want to verify it's not a hardware problem your best bet it is to try it with a program you know does work, any commercial game ROM will do (as long as it uses the same mapper of course).