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MEGA65 / mega65-core

MEGA65 FPGA core
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Fix Vertical flip bit not working on HW and adding feature -ve y_offset #799

Closed RetroCogs closed 2 months ago

RetroCogs commented 2 months ago

This is to address issue #796

This is using bit 4 of screen ram byte 1 when GOTOX is set to specify that the y_offset should be subtracted from the glyph_data_address.

This also fixes the issue that when vertical flip bit was set, y_offset would be ignored.

Tested FirstShot, all RetroCogs tutorials, Unicone, Showdown, IntroDisk #1 RRB Demo, Xanadu demo

RetroCogs commented 2 months ago

So yes, when nve_offset bit is set the offset is subracted rather than the default of added.

This also fixes the fact that when vertical flip bit was set it would ignore the y_offset.

I'm happy to add some tests similar to test_671.c as a separate pull request into mega65_tools.