Top two lines of playfield not showing

[marienbad]

I tried to write some code to display a playfield.  I used the framework from the Taswegian tutorial, and nicked a bit of code from the Spiceware tutorial (by Mr Spice - having seen Dune, I need to ask, should I be worried? Are giant sandworms going to come after me? ;) ) to display a playfield.  Each "line" should be 8 scanlines high, which is generally the case, but the top two lines are missing and I cannot see why.  All the data is there, and the rest of it is displayed correctly.  I am running it on Stella and other things seem to run fine, so I don't think I have done anything to Stella to mess it up.

 

I did wonder if it was something to do with the arena height being different in the collect tutorial, but I am using ldy #192 as the line counter.

test_kernel.zip

[+Andrew Davie]

You have not initialised "x" for the VerticalBlank delay loop.

Since it exits at the bottom of frame with x=30, that loop probably only gives you 6 scanlines instead of the expected 36.

You can use cmd-L to show scanline count in stella (or the windows equivalent).

 

[+Andrew Davie]

Also, the following are (or should be) invalid lines...

 

			#lda #0
			#sta COLUBK

Lines are commented-out/disabled with a ";".  I'm surprised dasm didn't flag these as errors.

[+SpiceWare]

3 hours ago, marienbad said:

I need to ask, should I be worried?

 

The Spice must flow

 

 

 

[marienbad]

6 hours ago, Andrew Davie said:

You have not initialised "x" for the VerticalBlank delay loop.

Since it exits at the bottom of frame with x=30, that loop probably only gives you 6 scanlines instead of the expected 36.

You can use cmd-L to show scanline count in stella (or the windows equivalent).

 

Thank you so much, so obvious when it is pointed out!

 

[marienbad]

4 hours ago, SpiceWare said:

 

The Spice must flow

 

 

 

Class - Old Skool FTW! Can't beat a bit of Rave.  Charly says: "Always tell your mummy before you go off somewhere"