From 4cb802bc68a182fdb5b28bf6e3484453e6afde54 Mon Sep 17 00:00:00 2001
From: angelosa <lordkale4@gmail.com>
Date: Tue, 15 Nov 2022 23:55:38 +0100
Subject: [PATCH] olympia/portrait.cpp: simplify scroll hookup

---
 src/mame/olympia/portrait.cpp | 17 +++++++----------
 src/mame/olympia/portrait.h   |  3 +--
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/src/mame/olympia/portrait.cpp b/src/mame/olympia/portrait.cpp
index 96ead30f8fd..39aee701464 100644
--- a/src/mame/olympia/portrait.cpp
+++ b/src/mame/olympia/portrait.cpp
@@ -123,16 +123,13 @@ void portrait_state::ctrl_w(uint8_t data)
 	output().set_value("photo", (data >> 7) & 1);
 }
 
-// $9235-$9236 raw scroll values up to 512
-// $9236 bit 0 defines which of these are used
-void portrait_state::positive_scroll_w(uint8_t data)
+// $9235-$9236 raw scroll values up to 511
+// $9236 bit 0 defines if $a018 or $a019 is used during active frame
+void portrait_state::scroll_w(offs_t offset, uint8_t data)
 {
 	m_scroll = data;
-}
-
-void portrait_state::negative_scroll_w(uint8_t data)
-{
-	m_scroll = 511 - (data ^ 0xff);
+	if (offset & 1)
+		m_scroll += 256;
 }
 
 void portrait_state::portrait_map(address_map &map)
@@ -149,8 +146,8 @@ void portrait_state::portrait_map(address_map &map)
 	map(0xa008, 0xa008).portr("SYSTEM").w(FUNC(portrait_state::ctrl_w));
 	map(0xa010, 0xa010).portr("INPUTS");
 	// $a018 reads go to $920f, never really read up?
-	map(0xa018, 0xa018).nopr().w(FUNC(portrait_state::positive_scroll_w));
-	map(0xa019, 0xa019).w(FUNC(portrait_state::negative_scroll_w));
+	map(0xa018, 0xa018).nopr();
+	map(0xa018, 0xa019).w(FUNC(portrait_state::scroll_w));
 	map(0xa800, 0xa83f).ram().share("nvram");
 	map(0xffff, 0xffff).nopr(); // on POST only, value discarded, likely just a bug
 }
diff --git a/src/mame/olympia/portrait.h b/src/mame/olympia/portrait.h
index 5b15bfc0c1d..e13df0ea59c 100644
--- a/src/mame/olympia/portrait.h
+++ b/src/mame/olympia/portrait.h
@@ -36,8 +36,7 @@ protected:
 
 private:
 	void ctrl_w(uint8_t data);
-	void positive_scroll_w(uint8_t data);
-	void negative_scroll_w(uint8_t data);
+	void scroll_w(offs_t offset, uint8_t data);
 	void bgvideo_write(offs_t offset, uint8_t data);
 	void fgvideo_write(offs_t offset, uint8_t data);