From 94b1c37fb20a38068167a4bd04cc8549d66ae6b5 Mon Sep 17 00:00:00 2001 From: Thomas Harte Date: Sun, 8 Apr 2018 18:51:37 -0400 Subject: [PATCH] Slightly simplifies bus decoding. --- Machines/Commodore/Vic-20/Vic20.cpp | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/Machines/Commodore/Vic-20/Vic20.cpp b/Machines/Commodore/Vic-20/Vic20.cpp index 0ad87a11c..0a80fa485 100644 --- a/Machines/Commodore/Vic-20/Vic20.cpp +++ b/Machines/Commodore/Vic-20/Vic20.cpp @@ -546,12 +546,12 @@ class ConcreteMachine: if(isReadOperation(operation)) { uint8_t result = processor_read_memory_map_[address >> 10] ? processor_read_memory_map_[address >> 10][address & 0x3ff] : 0xff; if((address&0xfc00) == 0x9000) { - if((address&0xff00) == 0x9000) { + if(!(address&0x100)) { update_video(); result &= mos6560_->get_register(address); } - if((address&0xfc10) == 0x9010) result &= user_port_via_.get_register(address); - if((address&0xfc20) == 0x9020) result &= keyboard_via_.get_register(address); + if(address & 0x10) result &= user_port_via_.get_register(address); + if(address & 0x20) result &= keyboard_via_.get_register(address); } *value = result; @@ -630,13 +630,17 @@ class ConcreteMachine: update_video(); ram[address & 0x3ff] = *value; } + // Anything between 0x9000 and 0x9400 is the IO area. if((address&0xfc00) == 0x9000) { - if((address&0xff00) == 0x9000) { + // The VIC is selected by bit 8 = 0 + if(!(address&0x100)) { update_video(); mos6560_->set_register(address, *value); } - if((address&0xfc10) == 0x9010) user_port_via_.set_register(address, *value); - if((address&0xfc20) == 0x9020) keyboard_via_.set_register(address, *value); + // The first VIA is selected by bit 4 = 1. + if(address & 0x10) user_port_via_.set_register(address, *value); + // The second VIA is selected by bit 5 = 1. + if(address & 0x20) keyboard_via_.set_register(address, *value); } }