diff --git a/Components/9918/Implementation/9918.cpp b/Components/9918/Implementation/9918.cpp
index 715140843..628f1566a 100644
--- a/Components/9918/Implementation/9918.cpp
+++ b/Components/9918/Implementation/9918.cpp
@@ -218,9 +218,7 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
// Convert 456 clocked half cycles per line to 342 internal cycles per line;
// the internal clock is 1.5 times the nominal 3.579545 Mhz that I've advertised
// for this part. So multiply by three quarters.
- int int_cycles = int(cycles.as_integral() * 3) + this->cycles_error_;
- this->cycles_error_ = int_cycles & 3;
- int_cycles >>= 2;
+ int int_cycles = this->clock_converter_.to_internal(cycles.as<int>());
if(!int_cycles) return;
// There are two intertwined processes here, 'writing' (which means writing to the
@@ -236,7 +234,10 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
if(write_cycles_pool) {
// Determine how much writing to do.
- const int write_cycles = std::min(342 - this->write_pointer_.column, write_cycles_pool);
+ const int write_cycles = std::min(
+ this->clock_converter_.CyclesPerLine - this->write_pointer_.column,
+ write_cycles_pool
+ );
const int end_column = this->write_pointer_.column + write_cycles;
LineBuffer &line_buffer = this->line_buffers_[this->write_pointer_.row];
@@ -274,16 +275,16 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
// Perform memory accesses.
// ------------------------
#define fetch(function) \
- if(final_window != 171) { \
+ if(final_window != this->clock_converter_.AccessWindowCyclesPerLine) { \
function<true>(first_window, final_window);\
} else {\
function<false>(first_window, final_window);\
}
- // column_ and end_column are in 342-per-line cycles;
- // adjust them to a count of windows.
- const int first_window = this->write_pointer_.column >> 1;
- const int final_window = end_column >> 1;
+ // Adjust column_ and end_column to the access-window clock before calling
+ // the mode-applicable fetch function.
+ const int first_window = this->clock_converter_.to_access_clock(this->write_pointer_.column);
+ const int final_window = this->clock_converter_.to_access_clock(end_column);
if(first_window != final_window) {
switch(line_buffer.line_mode) {
case LineMode::Text: fetch(this->template fetch_tms_text); break;
@@ -336,7 +337,7 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
this->write_pointer_.column = end_column;
write_cycles_pool -= write_cycles;
- if(this->write_pointer_.column == 342) {
+ if(this->write_pointer_.column == this->clock_converter_.CyclesPerLine) {
this->write_pointer_.column = 0;
this->write_pointer_.row = (this->write_pointer_.row + 1) % this->mode_timing_.total_lines;
LineBuffer &next_line_buffer = this->line_buffers_[this->write_pointer_.row];
@@ -345,7 +346,7 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
this->set_current_screen_mode();
// Based on the output mode, pick a line mode.
- next_line_buffer.first_pixel_output_column = 86;
+ next_line_buffer.first_pixel_output_column = 86; // TODO: these should be a function of ClockConverter::CyclesPerLine.
next_line_buffer.next_border_column = 342;
this->mode_timing_.maximum_visible_sprites = 4;
switch(this->screen_mode_) {
@@ -379,25 +380,31 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
if(read_cycles_pool) {
// Determine how much time has passed in the remainder of this line, and proceed.
- const int target_read_cycles = std::min(342 - this->read_pointer_.column, read_cycles_pool);
+ const int target_read_cycles = std::min(
+ this->clock_converter_.CyclesPerLine - this->read_pointer_.column,
+ read_cycles_pool
+ );
int read_cycles_performed = 0;
uint32_t next_cram_value = 0;
while(read_cycles_performed < target_read_cycles) {
+ int read_cycles = target_read_cycles - read_cycles_performed;
+ if(!read_cycles) continue;
+
const uint32_t cram_value = next_cram_value;
next_cram_value = 0;
- int read_cycles = target_read_cycles - read_cycles_performed;
- if(!this->upcoming_cram_dots_.empty() && this->upcoming_cram_dots_.front().location.row == this->read_pointer_.row) {
- int time_until_dot = this->upcoming_cram_dots_.front().location.column - this->read_pointer_.column;
+ if constexpr (is_sega_vdp(personality)) {
+ if(!this->upcoming_cram_dots_.empty() && this->upcoming_cram_dots_.front().location.row == this->read_pointer_.row) {
+ int time_until_dot = this->upcoming_cram_dots_.front().location.column - this->read_pointer_.column;
- if(time_until_dot < read_cycles) {
- read_cycles = time_until_dot;
- next_cram_value = this->upcoming_cram_dots_.front().value;
- this->upcoming_cram_dots_.erase(this->upcoming_cram_dots_.begin());
+ if(time_until_dot < read_cycles) {
+ read_cycles = time_until_dot;
+ next_cram_value = this->upcoming_cram_dots_.front().value;
+ this->upcoming_cram_dots_.erase(this->upcoming_cram_dots_.begin());
+ }
}
}
- if(!read_cycles) continue;
read_cycles_performed += read_cycles;
const int end_column = this->read_pointer_.column + read_cycles;
@@ -418,6 +425,7 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
#define border(left, right) intersect(left, right, this->output_border(end - start, cram_value))
+ // TODO: CRT clock might need to change?
if(line_buffer.line_mode == LineMode::Refresh || this->read_pointer_.row > this->mode_timing_.pixel_lines) {
if(this->read_pointer_.row >= this->mode_timing_.first_vsync_line && this->read_pointer_.row < this->mode_timing_.first_vsync_line+4) {
// Vertical sync.
@@ -507,7 +515,7 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
}
read_cycles_pool -= target_read_cycles;
- if(this->read_pointer_.column == 342) {
+ if(this->read_pointer_.column == this->clock_converter_.CyclesPerLine) {
this->read_pointer_.column = 0;
this->read_pointer_.row = (this->read_pointer_.row + 1) % this->mode_timing_.total_lines;
}
@@ -750,11 +758,6 @@ uint8_t TMS9918<personality>::read(int address) {
return result;
}
-template <Personality personality>
-HalfCycles Base<personality>::half_cycles_before_internal_cycles(int internal_cycles) const {
- return HalfCycles(((internal_cycles << 2) + (2 - cycles_error_)) / 3);
-}
-
template <Personality personality>
HalfCycles TMS9918<personality>::get_next_sequence_point() const {
if(!this->generate_interrupts_ && !this->enable_line_interrupts_) return HalfCycles::max();
@@ -769,7 +772,7 @@ HalfCycles TMS9918<personality>::get_next_sequence_point() const {
) % frame_length;
if(!time_until_frame_interrupt) time_until_frame_interrupt = frame_length;
- if(!this->enable_line_interrupts_) return this->half_cycles_before_internal_cycles(time_until_frame_interrupt);
+ if(!this->enable_line_interrupts_) return this->clock_converter_.half_cycles_before_internal_cycles(time_until_frame_interrupt);
// Calculate when the next line interrupt will occur.
int next_line_interrupt_row = -1;
@@ -797,17 +800,17 @@ HalfCycles TMS9918<personality>::get_next_sequence_point() const {
// the frame end interrupt or no interrupt pending as appropriate.
if(next_line_interrupt_row == -1) {
return this->generate_interrupts_ ?
- this->half_cycles_before_internal_cycles(time_until_frame_interrupt) :
+ this->clock_converter_.half_cycles_before_internal_cycles(time_until_frame_interrupt) :
HalfCycles::max();
}
// Figure out the number of internal cycles until the next line interrupt, which is the amount
// of time to the next tick over and then next_line_interrupt_row - row_ lines further.
const int local_cycles_until_line_interrupt = cycles_to_next_interrupt_threshold + (next_line_interrupt_row - line_of_next_interrupt_threshold) * 342;
- if(!this->generate_interrupts_) return this->half_cycles_before_internal_cycles(local_cycles_until_line_interrupt);
+ if(!this->generate_interrupts_) return this->clock_converter_.half_cycles_before_internal_cycles(local_cycles_until_line_interrupt);
// Return whichever interrupt is closer.
- return this->half_cycles_before_internal_cycles(std::min(local_cycles_until_line_interrupt, time_until_frame_interrupt));
+ return this->clock_converter_.half_cycles_before_internal_cycles(std::min(local_cycles_until_line_interrupt, time_until_frame_interrupt));
}
template <Personality personality>
@@ -825,7 +828,7 @@ HalfCycles TMS9918<personality>::get_time_until_line(int line) {
line += this->mode_timing_.total_lines;
}
- return this->half_cycles_before_internal_cycles(cycles_to_next_interrupt_threshold + (line - line_of_next_interrupt_threshold)*342);
+ return this->clock_converter_.half_cycles_before_internal_cycles(cycles_to_next_interrupt_threshold + (line - line_of_next_interrupt_threshold)*342);
}
template <Personality personality>
diff --git a/Components/9918/Implementation/9918Base.hpp b/Components/9918/Implementation/9918Base.hpp
index 396920ee9..93350cfcd 100644
--- a/Components/9918/Implementation/9918Base.hpp
+++ b/Components/9918/Implementation/9918Base.hpp
@@ -11,6 +11,7 @@
#include "../../../Outputs/CRT/CRT.hpp"
#include "../../../ClockReceiver/ClockReceiver.hpp"
+#include "ClockConverter.hpp"
#include <array>
#include <cassert>
@@ -199,11 +200,7 @@ template <Personality personality> struct Base {
uint8_t text_colour_ = 0;
uint8_t background_colour_ = 0;
- // This implementation of this chip officially accepts a 3.58Mhz clock, but runs
- // internally at 5.37Mhz. The following two help to maintain a lossless conversion
- // from the one to the other.
- int cycles_error_ = 0;
- HalfCycles half_cycles_before_internal_cycles(int internal_cycles) const;
+ ClockConverter<personality> clock_converter_;
// Internal mechanisms for position tracking.
int latched_column_ = 0;
diff --git a/Components/9918/Implementation/ClockConverter.hpp b/Components/9918/Implementation/ClockConverter.hpp
new file mode 100644
index 000000000..da4b15c16
--- /dev/null
+++ b/Components/9918/Implementation/ClockConverter.hpp
@@ -0,0 +1,64 @@
+//
+// ClockConverter.hpp
+// Clock Signal
+//
+// Created by Thomas Harte on 01/01/2023.
+// Copyright © 2023 Thomas Harte. All rights reserved.
+//
+
+#ifndef ClockConverter_hpp
+#define ClockConverter_hpp
+
+#include "../9918.hpp"
+
+namespace TI {
+namespace TMS {
+
+template <Personality personality> class ClockConverter {
+ public:
+ /*!
+ Converts a number of **half-cycles** to an internal number
+ of **cycles**.
+ */
+ int to_internal(int source) {
+ // Default behaviour is top apply a multiplication by 3/4.
+ const int result = source * 3 + cycles_error_;
+ cycles_error_ = result & 3;
+ return result >> 2;
+ }
+
+ /*!
+ Provides the number of external cycles that will need to pass in order to advance
+ _at least_ @c internal_cycles into the future.
+ */
+ HalfCycles half_cycles_before_internal_cycles(int internal_cycles) const {
+ return HalfCycles(
+ ((internal_cycles << 2) + (2 - cycles_error_)) / 3
+ );
+ }
+
+ /*
+ Converts a position in internal cycles to its corresponding position
+ on the access-window clock.
+ */
+ static constexpr int to_access_clock(int source) {
+ return source >> 1;
+ }
+
+ /// The number of internal cycles in a single line.
+ constexpr static int CyclesPerLine = 342;
+
+ /// Indicates the number of access-window cycles in a single line.
+ constexpr static int AccessWindowCyclesPerLine = 171;
+
+ private:
+ // This implementation of this chip officially accepts a 3.58Mhz clock, but runs
+ // internally at 5.37Mhz. The following two help to maintain a lossless conversion
+ // from the one to the other.
+ int cycles_error_ = 0;
+};
+
+}
+}
+
+#endif /* ClockConverter_hpp */
diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
index 595676063..ef9b2324a 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
@@ -1317,6 +1317,7 @@
4B3FE75C1F3CF68B00448EE4 /* CPM.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = CPM.cpp; path = Parsers/CPM.cpp; sourceTree = "<group>"; };
4B3FE75D1F3CF68B00448EE4 /* CPM.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = CPM.hpp; path = Parsers/CPM.hpp; sourceTree = "<group>"; };
4B43983829620FB1006B0BFC /* 9918.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = 9918.cpp; sourceTree = "<group>"; };
+ 4B43983C29621024006B0BFC /* ClockConverter.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = ClockConverter.hpp; sourceTree = "<group>"; };
4B448E7F1F1C45A00009ABD6 /* TZX.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = TZX.cpp; sourceTree = "<group>"; };
4B448E801F1C45A00009ABD6 /* TZX.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = TZX.hpp; sourceTree = "<group>"; };
4B448E821F1C4C480009ABD6 /* PulseQueuedTape.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = PulseQueuedTape.cpp; sourceTree = "<group>"; };
@@ -4734,6 +4735,7 @@
children = (
4B43983829620FB1006B0BFC /* 9918.cpp */,
4BD388411FE34E010042B588 /* 9918Base.hpp */,
+ 4B43983C29621024006B0BFC /* ClockConverter.hpp */,
);
path = Implementation;
sourceTree = "<group>";