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Divide input pixel rate.

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This commit is contained in:
Thomas Harte 2024-03-21 11:03:28 -04:00
parent 417c6c4629
commit 847dba8f07
1 changed files with 28 additions and 2 deletions
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30
Machines/Acorn/Archimedes/Video.hpp
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@ -108,6 +108,18 @@ struct Video {
case 0xe0:
logger.error().append("TODO: video control: %08x", value);
// Set pixel rate.
//
// TODO: possibly do this as a multiplier on position counts and a divider on pixels,
// to maintain a consistent CRT data clock?
switch(value & 0b11) {
case 0b00: clock_divider_ = 12; break; // 4Mhz count.
case 0b01: clock_divider_ = 8; break; // 6Mhz count.
case 0b10: clock_divider_ = 6; break; // 8Mhz count.
case 0b11: clock_divider_ = 4; break; // i.e. 48/4 = 12Mhz position counting clock.
}
sub_clock_ = 0;
break;
//
@ -123,7 +135,6 @@ struct Video {
sound_.set_frequency(value & 0x7f);
break;
default:
logger.error().append("TODO: unrecognised VIDC write of %08x", value);
break;
@ -131,6 +142,18 @@ struct Video {
}
void tick() {
// Apply clock divider to get 8, 12, 16 or 24 Mhz pixel rate as user-selected,
// which since all event positioning is at two-pixel boundaries means a
// 4, 6, 8 or 12 Mhz counting clock.
//
// tick() is called at 12Mhz.
sub_clock_ += 4; // Count at 48 Mhz.
if(sub_clock_ < clock_divider_) {
return;
}
sub_clock_ -= clock_divider_;
// TODO: real output. For now, just count up to complete frames and pretend a retrace goes there.
++position_;
if(position_ >= horizontal_.period * vertical_.period) {
entered_sync_ = true;
@ -152,7 +175,7 @@ private:
SoundT &sound_;
// TODO: real video output.
int position_ = 0;
uint32_t position_ = 0;
struct Dimension {
uint32_t period = 0;
@ -166,6 +189,9 @@ private:
};
Dimension horizontal_, vertical_;
bool entered_sync_ = false;
int sub_clock_ = 0;
int clock_divider_ = 0;
};
}