mirror of https://gitlab.com/camelot/kickc.git
119 lines
8.0 KiB
C
119 lines
8.0 KiB
C
// MEGA65 Memory Mapper allows the 6502 CPU to access up to 256MB of memory by remapping where the eight 8K blocks point in real memory.
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// The memory mapping is configured through the new MAP instruction of the MOS 4510.
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// https://mega65.org/
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// https://mega.scryptos.com/sharefolder-link/MEGA/MEGA65+filehost/Docs/MEGA65-Book_draft.pdf
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// https://github.com/MEGA65/mega65-core/blob/master/src/vhdl/gs4510.vhdl
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// http://www.zimmers.net/cbmpics/cbm/c65/c65manual.txt
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// http://anyplatform.net/media/guides/cpus/65xx%20Processor%20Data.txt
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// Remap some of the eight 8K memory blocks in the 64K address space of the 6502 to point somewhere else in the first 1MB memory space of the MEGA65.
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// After the remapping the CPU will access the mapped memory whenever it uses instructions that access a remapped block.
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// See section 2.3.4 in http://www.zimmers.net/cbmpics/cbm/c65/c65manual.txt for a description of the CPU memory remapper of the C65.
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// remapBlocks: Indicates which 8K blocks of the 6502 address space to remap. Each bit represents one 8K block
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// - bit 0 Memory block $0000-$1fff. Use constant MEMORYBLOCK_0000.
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// - bit 1 Memory block $2000-$3fff. Use constant MEMORYBLOCK_2000.
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// - bit 2 Memory block $4000-$5fff. Use constant MEMORYBLOCK_4000.
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// - bit 3 Memory block $6000-$7fff. Use constant MEMORYBLOCK_6000.
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// - bit 4 Memory block $8000-$9fff. Use constant MEMORYBLOCK_8000.
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// - bit 5 Memory block $a000-$bfff. Use constant MEMORYBLOCK_A000.
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// - bit 6 Memory block $c000-$dfff. Use constant MEMORYBLOCK_C000.
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// - bit 7 Memory block $e000-$ffff. Use constant MEMORYBLOCK_E000.
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// lowerPageOffset: Offset that will be added to any remapped blocks in the lower 32K of memory (block 0-3).
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// The offset is a page offset (meaning it is multiplied by 0x100). Only the lower 12bits of the passed value is used.
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// - If block 0 ($0000-$1fff) is remapped it will point to lowerPageOffset*$100.
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// - If block 1 ($2000-$3fff) is remapped it will point to lowerPageOffset*$100 + $2000.
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// - If block 2 ($4000-$5fff) is remapped it will point to lowerPageOffset*$100 + $4000.
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// - If block 3 ($6000-$7fff) is remapped it will point to lowerPageOffset*$100 + $6000.
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// upperPageOffset: Offset that will be added to any remapped blocks in the upper 32K of memory (block 4-7).
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// The offset is a page offset (meaning it is multiplied by 0x100). Only the lower 12bits of the passed value is used.
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// - If block 4 ($8000-$9fff) is remapped it will point to upperPageOffset*$100 + $8000
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// - If block 5 ($a000-$bfff) is remapped it will point to upperPageOffset*$100 + $a000.
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// - If block 6 ($c000-$dfff) is remapped it will point to upperPageOffset*$100 + $c000.
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// - If block 7 ($e000-$ffff) is remapped it will point to upperPageOffset*$100 + $e000.
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void memoryRemap(unsigned char remapBlocks, unsigned int lowerPageOffset, unsigned int upperPageOffset) {
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// lower blocks offset page low
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char aVal = BYTE0(lowerPageOffset);
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// lower blocks to map + lower blocks offset high nibble
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char xVal = (remapBlocks << 4) | (BYTE1(lowerPageOffset) & 0xf);
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// upper blocks offset page
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char yVal = BYTE0(upperPageOffset);
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// upper blocks to map + upper blocks offset page high nibble
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char zVal = (remapBlocks & 0xf0) | (BYTE1(upperPageOffset) & 0xf);
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asm {
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lda aVal // lower blocks offset page low
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ldx xVal // lower blocks to map + lower blocks offset high nibble
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ldy yVal // upper blocks offset page
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ldz zVal // upper blocks to map + upper blocks offset page high nibble
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map
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eom
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}
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}
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// Remap a single 8K memory block in the 64K address space of the 6502 to point somewhere else in the first 1MB memory space of the MEGA65.
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// All the other 8K memory blocks will not be mapped and will point to their own address in the lowest 64K of the MEGA65 memory.
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// blockPage: Page address of the 8K memory block to remap (ie. the block that is remapped is $100 * the passed page address.)
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// memoryPage: Page address of the memory that the block should point to in the 1MB memory space of the MEGA65.
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// Ie. the memory that will be pointed to is $100 * the passed page address. Only the lower 12bits of the passed value is used.
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void memoryRemapBlock(unsigned char blockPage, unsigned int memoryPage) {
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// Find the page offset (the number of pages to offset the block)
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unsigned int pageOffset = memoryPage-blockPage;
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// Which block is being remapped? (0-7)
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char block = blockPage / 0x20;
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char blockBits = 1<<block;
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memoryRemap(blockBits, pageOffset, pageOffset);
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}
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// Remap some of the eight 8K memory blocks in the 64K address space of the 6502 to point somewhere else in the entire 256MB memory space of the MEGA65.
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// After the remapping the CPU will access the mapped memory whenever it uses instructions that access a remapped block.
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// See section 2.3.4 in http://www.zimmers.net/cbmpics/cbm/c65/c65manual.txt for a description of the CPU memory remapper of the C65.
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// See Appendix G in file:///Users/jespergravgaard/Downloads/MEGA65-Book_draft%20(5).pdf for a description of the CPU memory remapper of the MEGA65.
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// remapBlocks: Indicates which 8K blocks of the 6502 address space to remap. Each bit represents one 8K block
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// - bit 0 Memory block $0000-$1fff. Use constant MEMORYBLOCK_0000.
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// - bit 1 Memory block $2000-$3fff. Use constant MEMORYBLOCK_2000.
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// - bit 2 Memory block $4000-$5fff. Use constant MEMORYBLOCK_4000.
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// - bit 3 Memory block $6000-$7fff. Use constant MEMORYBLOCK_6000.
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// - bit 4 Memory block $8000-$9fff. Use constant MEMORYBLOCK_8000.
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// - bit 5 Memory block $a000-$bfff. Use constant MEMORYBLOCK_A000.
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// - bit 6 Memory block $c000-$dfff. Use constant MEMORYBLOCK_C000.
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// - bit 7 Memory block $e000-$ffff. Use constant MEMORYBLOCK_E000.
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// lowerPageOffset: Offset that will be added to any remapped blocks in the lower 32K of memory (block 0-3).
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// The offset is a page offset (meaning it is multiplied by 0x100). Only the lower 20bits of the passed value is used.
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// - If block 0 ($0000-$1fff) is remapped it will point to lowerPageOffset*$100.
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// - If block 1 ($2000-$3fff) is remapped it will point to lowerPageOffset*$100 + $2000.
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// - If block 2 ($4000-$5fff) is remapped it will point to lowerPageOffset*$100 + $4000.
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// - If block 3 ($6000-$7fff) is remapped it will point to lowerPageOffset*$100 + $6000.
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// upperPageOffset: Offset that will be added to any remapped blocks in the upper 32K of memory (block 4-7).
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// The offset is a page offset (meaning it is multiplied by 0x100). Only the lower 20bits of the passed value is used.
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// - If block 4 ($8000-$9fff) is remapped it will point to upperPageOffset*$100 + $8000
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// - If block 5 ($a000-$bfff) is remapped it will point to upperPageOffset*$100 + $a000.
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// - If block 6 ($c000-$dfff) is remapped it will point to upperPageOffset*$100 + $c000.
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// - If block 7 ($e000-$ffff) is remapped it will point to upperPageOffset*$100 + $e000.
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void memoryRemap256M(unsigned char remapBlocks, unsigned long lowerPageOffset, unsigned long upperPageOffset) {
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// lower blocks offset megabytes
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char lMb = BYTE1((unsigned int)(lowerPageOffset>>4));
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// upper blocks offset megabytes
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char uMb = BYTE1((unsigned int)(upperPageOffset>>4));
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// lower blocks offset page low
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char aVal = BYTE0(lowerPageOffset);
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// lower blocks to map + lower blocks offset high nibble
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char xVal = (remapBlocks << 4) | (BYTE1(lowerPageOffset) & 0xf);
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// upper blocks offset page
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char yVal = BYTE0(upperPageOffset);
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// upper blocks to map + upper blocks offset page high nibble
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char zVal = (remapBlocks & 0xf0) | (BYTE1(upperPageOffset) & 0xf);
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asm {
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lda lMb // lower blocks offset megabytes
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ldx #$0f // lower signal for MB offset
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ldy uMb // upper blocks offset megabytes
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ldz #$0f // upper signal for MB offset
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map
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lda aVal // lower blocks offset page low
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ldx xVal // lower blocks to map + lower blocks offset high nibble
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ldy yVal // upper blocks offset page
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ldz zVal // upper blocks to map + upper blocks offset page high nibble
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map
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eom
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}
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}
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