Confused about VRAM nametables (tiletables) sizes
Posted: Wed Apr 30, 2014 11:15 pm
Hi guys!
I was having a look at Fonzie's "The VDP in 16 Pics" when I noticed about a "supposed" free-to-use 128 tile area I didn't know about:
That discovery made my day... for a while.
I made a quick test ... writing over that area brought no problem at all. Good, good.
And then I did another one ...
I tested the same, writing tiles at "1920 tile position" (VRAM 0xF000) but ...
My background became awfully glitched.
After a while I discovered that that thing was happening when my BPLAN tilemap heigh was exceding of 32 rows. And that made that "supposed to be a free-to-use area" to be filled whith some data belonging to BPLAN nametable.
This is a simplified test using sgdk:
OK with empirical then.
Anyhow, and looking back at Fonzie's VRAM table, I wonder how can it be like that (each plane consuming that amount of data) knowing that H-Scroll and sprite tables would be overwritten if APLAN (at Fonzie's table positioning case) has, for instance, 64 rows drawn.
Yup, I remain a bit confused
I was having a look at Fonzie's "The VDP in 16 Pics" when I noticed about a "supposed" free-to-use 128 tile area I didn't know about:
That discovery made my day... for a while.
I made a quick test ... writing over that area brought no problem at all. Good, good.
And then I did another one ...
I tested the same, writing tiles at "1920 tile position" (VRAM 0xF000) but ...
My background became awfully glitched.
After a while I discovered that that thing was happening when my BPLAN tilemap heigh was exceding of 32 rows. And that made that "supposed to be a free-to-use area" to be filled whith some data belonging to BPLAN nametable.
This is a simplified test using sgdk:
OK with empirical then.
Anyhow, and looking back at Fonzie's VRAM table, I wonder how can it be like that (each plane consuming that amount of data) knowing that H-Scroll and sprite tables would be overwritten if APLAN (at Fonzie's table positioning case) has, for instance, 64 rows drawn.
Yup, I remain a bit confused