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Merge pull request #1182 from ryandesign/apple-ii-floating-bus-2

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Fix Apple II/II+/IIe floating bus issues
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Thomas Harte 2023-10-28 15:46:35 -04:00 committed by GitHub
commit b98f54545f
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1 changed files with 84 additions and 13 deletions
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97
Machines/Apple/AppleII/Video.hpp
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@ -129,14 +129,56 @@ template <class BusHandler, bool is_iie> class Video: public VideoBase {
*/
uint8_t get_last_read_value(Cycles offset) {
// Rules of generation:
// (1) a complete sixty-five-cycle scan line consists of sixty-five consecutive bytes of
// display buffer memory that starts twenty-five bytes prior to the actual data to be displayed.
// (2) During VBL the data acts just as if it were starting a whole new frame from the beginning, but
// it never finishes this pseudo-frame. After getting one third of the way through the frame (to
// scan line $3F), it suddenly repeats the previous six scan lines ($3A through $3F) before aborting
// to begin the next true frame.
// FOR ALL MODELS IN ALL MODES:
//
// Source: Have an Apple Split by Bob Bishop; http://rich12345.tripod.com/aiivideo/softalk.html
// - "Screen memory is divided into 128-byte segments. Each segment is divided into the FIRST 40, the
// SECOND 40, the THIRD 40, and eight bytes of no man's memory (UNUSED 8)." (5-8*)
//
// - "The VBL base addresses are equal to the FIRST 40 base addresses minus eight bytes using 128-byte
// wraparound subtraction. Example: $400 minus $8 gives $478; not $3F8." (5-11*)
//
// - "The memory locations scanned during HBL prior to a displayed line are the 24 bytes just below the
// displayed area, using 128-byte wraparound addressing." (5-13*)
//
// - "The first address of HBL is always addressed twice consecutively" (5-11*)
//
// - "Memory scanned by lines 256 through 261 is identical to memory scanned by lines 250 through 255,
// so those six 64-byte sections are scanned twice" (5-13*)
// FOR II AND II+ ONLY (NOT IIE OR LATER) IN TEXT/LORES MODE ONLY (NOT HIRES):
//
// - "HBL scanned memory begins $18 bytes before display scanned memory plus $1000." (5-11*)
//
// - "Horizontal scanning wraps around at the 128-byte segment boundaries. Example: the address scanned
// before address $400 is $47F during VBL. The address scanned before $400 when VBL is false is
// $147F." (5-11*)
//
// - "the memory scanned during HBL is completely separate from the memory scanned during HBL´." (5-11*)
//
// - "HBL scanned memory is in an area normally taken up by Applesoft programs or Integer BASIC
// variables" (5-37*)
//
// - Figure 5.17 Screen Memory Scanning (5-37*)
// FOR IIE AND LATER IN ALL MODES AND II AND II+ IN HIRES MODE:
//
// - "HBL scanned memory begins $18 bytes before display scanned memory." (5-10**)
//
// - "Horizontal scanning wraps around at the 128-byte segment boundaries. Example: the address scanned
// before address $400 is $47F." (5-11**)
//
// - "during HBL, the memory locations that are scanned are in the displayed memory area." (5-13*)
//
// - "Programs written for the Apple II may well not perform correctly on the Apple IIe because of
// differences in scanning during HBL. In the Apple II, HBL scanned memory was separate from other
// display memory in TEXT/LORES scanning. In the Apple IIe, HBL scanned memory overlaps other scanned
// memory in TEXT/LORES scanning in similar fashion to HIRES scanning." (5-43**)
//
// - Figure 5.17 Display Memory Scanning (5-41**)
// Source: * Understanding the Apple II by Jim Sather
// Source: ** Understanding the Apple IIe by Jim Sather
// Determine column at offset.
int mapped_column = column_ + int(offset.as_integral());
@ -147,8 +189,21 @@ template <class BusHandler, bool is_iie> class Video: public VideoBase {
// Apply carry into the row counter.
int mapped_row = row_ + (mapped_column / 65);
mapped_column %= 65;
mapped_row %= 262;
mapped_column %= 65;
// Remember if we're in a horizontal blanking interval.
int hbl = mapped_column < 25;
// The first column is read twice.
if(mapped_column == 0) {
mapped_column = 1;
}
// Vertical blanking rows read eight bytes earlier.
if(mapped_row >= 192) {
mapped_column -= 8;
}
// Apple out-of-bounds row logic.
if(mapped_row >= 256) {
@ -157,8 +212,24 @@ template <class BusHandler, bool is_iie> class Video: public VideoBase {
mapped_row %= 192;
}
// Calculate the address and return the value.
// Calculate the address.
uint16_t read_address = uint16_t(get_row_address(mapped_row) + mapped_column - 25);
if(hbl) {
// Wraparound addressing within 128 byte sections.
if(mapped_row < 64) {
read_address += 128;
}
// On Apple II and II+ (not IIe or later) in text/lores mode (not hires), horizontal
// blanking bytes read from $1000 higher.
const GraphicsMode pixel_mode = graphics_mode(mapped_row);
if(!is_iie_ && ((pixel_mode == GraphicsMode::Text) || (pixel_mode == GraphicsMode::LowRes))) {
read_address += 0x1000;
}
}
// Read the address and return the value.
uint8_t value, aux_value;
bus_handler_.perform_read(read_address, 1, &value, &aux_value);
return value;
@ -168,20 +239,20 @@ template <class BusHandler, bool is_iie> class Video: public VideoBase {
@returns @c true if the display will be within vertical blank at now + @c offset; @c false otherwise.
*/
bool get_is_vertical_blank(Cycles offset) {
// Map that backwards from the internal pixels-at-start generation to pixels-at-end
// (so what was column 0 is now column 25).
// Determine column at offset.
int mapped_column = column_ + int(offset.as_integral());
// Map that backwards from the internal pixels-at-start generation to pixels-at-end
// (so what was column 0 is now column 25).
mapped_column += 25;
// Apply carry into the row counter and test it for location.
// Apply carry into the row counter.
int mapped_row = row_ + (mapped_column / 65);
mapped_row %= 262;
// Per http://www.1000bit.it/support/manuali/apple/technotes/iigs/tn.iigs.040.html
// "on the IIe, the screen is blanked when the bit is low".
return (mapped_row % 262) < 192;
return mapped_row < 192;
}
private: