Bottom half of sprites missing in MacAttack

C-BIOS is an open source BIOS for MSX computers.

Status: Alpha

Brought to you by: mthuurne

#21 Bottom half of sprites missing in MacAttack

Milestone: v1.0 (example)

Status: open

Owner: nobody

Labels: None

Priority: 5

Updated: 2017-01-28

Created: 2017-01-26

Creator: Manuel Bilderbeek

Private: No

When running MacAttack in C-BIOS (any version), the bottom half of the sprites are missing. Demo here: https://www.youtube.com/watch?v=sM7mWOGf1fA

I confirmed the same ROM works fine with e.g. a Toshiba HX-10 configuration.

Discussion

Maarten ter Huurne - 2017-01-28

It's not just the bottom halves that are missing: the problem is that 8x8 sprite size is active while it should be 16x16. This is controlled by bit1 of VDP R#1.

MacAttack writes 0xE2 to RG1SAV (0xF3E0) before calling CLRSPR (0x0069), expecting the VDP register to be updated with that value. The original BIOS does that, C-BIOS currently does not.

There is nothing in CLRSPR's documentation that suggests it should rewrite R#1, but we'll have to do it anyway for compatibility.

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Log in to post a comment.