diff --git a/Machines/Apple/AppleII/Video.hpp b/Machines/Apple/AppleII/Video.hpp index 1e84d2c04..1af8620ad 100644 --- a/Machines/Apple/AppleII/Video.hpp +++ b/Machines/Apple/AppleII/Video.hpp @@ -129,14 +129,56 @@ template 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 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 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 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: