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Introduced an explicit record of whether a video byte is latched. It's definitely incorrect to treat the latching of 0 as equivalent to no latching, as the byte that will eventually become video is not strongly implied.

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This commit is contained in:
Thomas Harte 2017-07-08 20:40:19 -04:00
parent 22389a5d2d
commit d6b87053bf
2 changed files with 7 additions and 3 deletions
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8
Machines/ZX8081/ZX8081.cpp
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@ -25,7 +25,8 @@ Machine::Machine() :
use_fast_tape_hack_(false),
tape_advance_delay_(0),
tape_is_automatically_playing_(false),
tape_is_playing_(false) {
tape_is_playing_(false),
has_latched_video_byte_(false) {
set_clock_rate(ZX8081ClockRate);
tape_player_.set_motor_control(true);
clear_all_keys();
@ -114,7 +115,7 @@ int Machine::perform_machine_cycle(const CPU::Z80::PartialMachineCycle &cycle) {
set_interrupt_line(true, -2);
set_interrupt_line(false);
}
if(latched_video_byte_) {
if(has_latched_video_byte_) {
size_t char_address = (size_t)((address & 0xfe00) | ((latched_video_byte_ & 0x3f) << 3) | line_counter_);
uint8_t mask = (latched_video_byte_ & 0x80) ? 0x00 : 0xff;
if(char_address < ram_base_) {
@ -124,7 +125,7 @@ int Machine::perform_machine_cycle(const CPU::Z80::PartialMachineCycle &cycle) {
}
video_->output_byte(latched_video_byte_);
latched_video_byte_ = 0;
has_latched_video_byte_ = false;
}
break;
@ -165,6 +166,7 @@ int Machine::perform_machine_cycle(const CPU::Z80::PartialMachineCycle &cycle) {
// just return the value as read.
if(is_opcode_read && address&0x8000 && !(value & 0x40) && !get_halt_line()) {
latched_video_byte_ = value;
has_latched_video_byte_ = true;
*cycle.value = 0;
} else *cycle.value = value;
}

2
Machines/ZX8081/ZX8081.hpp
View File

@ -98,7 +98,9 @@ class Machine:
bool is_zx81_;
bool nmi_is_enabled_;
int vsync_start_cycle_, vsync_end_cycle_;
uint8_t latched_video_byte_;
bool has_latched_video_byte_;
bool use_fast_tape_hack_;
bool use_automatic_tape_motor_control_;