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Document a little further.

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Thomas Harte
2025-10-02 09:30:33 -04:00
parent cbcc7c718e
commit a9abc0dd5f
1 changed files with 17 additions and 4 deletions
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Components/6845/CRTC6845.hpp
+17 -4
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@@ -217,6 +217,8 @@ public:
// Addressing.
//
// Start-of-line address: seeded with the programmed display start address upon a new frame;
// otherwise copied from the refresh address at the end of each line of characters.
const auto initial_line_address = line_address_;
if(new_frame) {
line_address_ = layout_.start_address;
@@ -224,6 +226,9 @@ public:
line_address_ = refresh_;
}
// Refresh address: seeded with the programmed display start address upon a new frame;
// otherwise copied from the start-of-line address is a new line is about to start;
// otherwise incremented across the line.
if(new_frame) {
refresh_ = layout_.start_address;
} else if(character_total_hit) {
@@ -232,8 +237,11 @@ public:
++refresh_;
}
// Follow hoglet's lead in means of avoiding the logic that informs line address b0 varying
// within a line if interlace mode is enabled/disabled.
//
// Per hoglet: b0 does not vary within a line even if you switch in/out of interlaced mode.
// He reproduces the same with extra state, which probably doesn't exist on the real device.
// This implementation follows his lead.
//
if(character_total_hit) {
line_is_interlaced_ = layout_.interlace_mode_ == InterlaceMode::SyncAndVideo;
}
@@ -377,6 +385,8 @@ public:
is_first_scanline_ = false;
}
// The extra-line flag holds true for a single line if one is needed to complete
// an odd interlaced field.
if(
character_total_hit &&
eof_latched_ &&
@@ -389,12 +399,15 @@ public:
extra_line_ = false;
}
// EOF (end of field) marks the end of the regular set of scans, including the adjustment area.
// It doesn't include the extra line added during odd interlaced fields.
if(new_frame) {
eof_latched_ = false;
} else if(eom_latched_ && !will_adjust_ && character_reset_history_.bit<2>()) {
eof_latched_ = true;
}
// Will-adjust indicates whether an adjustment area is upcoming; if so then it occurs after EOM.
if(new_frame) {
will_adjust_ = false;
} else if(character_reset_history_.bit<1>() && eom_latched_) {
@@ -405,7 +418,8 @@ public:
}
}
// EOM (end of main) marks the end of the visible set of rows, prior to any adjustment area. So it
// EOM (end of main) marks the end of the visible set of rows, prior to any adjustment area.
// It is set one cycle after the most-recent start of line.
if(new_frame) {
eom_latched_ = false;
} else if(character_reset_history_.bit<0>() && line_end_hit && row_counter_ == layout_.vertical.total) {
@@ -429,7 +443,6 @@ public:
)
);
// TODO: the above is clearly a quick-fix hack. Research better.
}