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Shunts CRAM dots into their proper place.

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This commit is contained in:
Thomas Harte 2018-10-26 20:06:51 -04:00
parent 521d603902
commit 05a5c7120e
2 changed files with 20 additions and 11 deletions
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6
Components/9918/9918.cpp
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@ -73,11 +73,9 @@ Base::Base(Personality p) :
mode_timing_.end_of_frame_interrupt_position.row = 193;
}
// Establish that output is 10 cycles after values have been read.
// This is definitely correct for the TMS; more research may be
// necessary for the other implemented VDPs.
// Establish that output is delayed after reading by `output_lag` cycles.
read_pointer_.row = 0;
read_pointer_.column = 342 - 11; // i.e. 11 cycles behind the write pointer.
read_pointer_.column = 342 - output_lag;
write_pointer_.row = 1;
write_pointer_.column = 0;
}

25
Components/9918/Implementation/9918Base.hpp
View File

@ -51,6 +51,8 @@ class Base {
}
protected:
const static int output_lag = 11; // i.e. pixel output will occur 11 cycles after corresponding data read.
// The default TMS palette.
const uint32_t palette[16] = {
palette_pack(0, 0, 0),
@ -340,16 +342,25 @@ class Base {
static_cast<uint8_t>(((read_ahead_buffer_ >> 4) & 3) * 255 / 3)
);
// Schedule a CRAM dot.
// Schedule a CRAM dot; this is scheduled for wherever it should appear
// on screen. So it's wherever the output stream would be now. Which
// is output_lag cycles ago from the point of view of the input stream.
upcoming_cram_dots_.emplace_back();
CRAMDot &dot = upcoming_cram_dots_.back();
dot.location.row = write_pointer_.row + (access_column / 342);
dot.location.column = access_column % 342;
dot.value = master_system_.colour_ram[ram_pointer_ & 0x1f];
// TODO: the location should actually be slightly in the past, as
// output trails memory reading; expose the length of that gap
// somewhere that makes it visible to here and adjust.
dot.location.column = write_pointer_.column - output_lag;
dot.location.row = write_pointer_.row;
// Handle before this row conditionally; then handle after (or, more realistically,
// exactly at the end of) naturally.
if(dot.location.column < 0) {
--dot.location.row;
dot.location.column += 342;
}
dot.location.row += dot.location.column / 342;
dot.location.column %= 342;
dot.value = master_system_.colour_ram[ram_pointer_ & 0x1f];
} else {
ram_[ram_pointer_ & 16383] = read_ahead_buffer_;
}