From f3eacf7566759e1772d6d8ecf916209d4b0c8689 Mon Sep 17 00:00:00 2001 From: arbee Date: Fri, 11 Jun 2021 21:21:42 -0400 Subject: apple2gs: correct vertical counter readback (GitHub #8156) [R. Belmont, Jeremy Rand] --- src/mame/drivers/apple2gs.cpp | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/src/mame/drivers/apple2gs.cpp b/src/mame/drivers/apple2gs.cpp index 88757ffc185..e0ec82d1be6 100644 --- a/src/mame/drivers/apple2gs.cpp +++ b/src/mame/drivers/apple2gs.cpp @@ -2186,7 +2186,12 @@ int apple2gs_state::get_vpos() { // as per IIgs Tech Note #39, this is simply scanline + 250 on NTSC (262 lines), // or scanline + 200 on PAL (312 lines) - return ((m_screen->vpos() + BORDER_TOP) % 262) + 250; + int vpos = m_screen->vpos() + (511 - BORDER_TOP + 6); + if (vpos > 511) + { + vpos -= (511 - 250); + } + return vpos; } void apple2gs_state::process_clock() -- cgit v1.2.3