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--- hardware:flashcarts [2023/08/18 22:03] – created clyde
+++ hardware:flashcarts [2024/11/22 09:40] (current) – clyde
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 ====== Flash Cartridges ======
-{{ :hardware:flashcart.jpg?400|}}
+{{ :hardware:flashcart.jpg?200}}
 This page covers information about the 2MB Flash Cartridge for the GameTank.
@@ Line 25: / Line 25: @@
 When LATCH goes from 0 to 1, the value of the shift register will take effect.
+The following code demonstrates a subroutine that pushes the contents of the Accumulator into the cartridge bank register. ''VIA'', ''ORA'', and ''DDRA'' are defined such that ''VIA+ORA'' is evaluated as $2801 by the assembler and ''VIA+DDRA'' is evaluated as $2803. A subroutine is also given for setting up the VIA to control cartridge banking, which should be called at least once before using ''ShiftHighBits''.
+<code 6502acme>
+SetupVIA:
+    LDA #%00000111
+    STA VIA+DDRA
+    LDA #$FF
+    STA VIA+ORA
+ShiftHighBits:
+	STA temp
+	LDA #$FF
+	STA VIA+ORA
+	LDA temp
+	ROR
+	ROR
+	ROR
+	ROR
+	ROR
+	AND #2
+	ORA #%00000100
+	STA VIA+ORA
+	ORA #1
+	STA VIA+ORA
+	LDA temp
+	ROR
+	ROR
+	ROR
+	ROR
+	AND #2
+	ORA #%00000100
+	STA VIA+ORA
+	ORA #1
+	STA VIA+ORA
+	LDA temp
+	ROR
+	ROR
+	ROR
+	AND #2
+	ORA #%00000100
+	STA VIA+ORA
+	ORA #1
+	STA VIA+ORA
+	LDA temp
+	ROR
+	ROR
+	AND #2
+	ORA #%00000100
+	STA VIA+ORA
+	ORA #1
+	STA VIA+ORA
+	LDA temp
+	ROR
+	AND #2
+	ORA #%00000100
+	STA VIA+ORA
+	ORA #1
+	STA VIA+ORA
+	LDA temp
+	AND #2
+	ORA #%00000100
+	STA VIA+ORA
+	ORA #1
+	STA VIA+ORA
+	LDA temp
+	ROL
+	AND #2
+	STA VIA+ORA
+	ORA #1
+	STA VIA+ORA
+	ORA #4
+	STA VIA+ORA
+	RTS
+</code>
+===== Reading from banked memory =====
+Any data that you want to access with the movable window should be referenced by its address relative to the start of its bank plus the cartridge port offset. So if you have data to access at $0, $4000, and $C000 bytes into your game binary you'd read from $8000 after setting the bank number to 0, 1, and 3 respectively.
+The last 16KB of your game binary are always accessible at $C000-$FFFF, and also accessible at $8000-$BFFF if the bank number has been set to 127 or 255.
+Some toolchains like cc65 have features that can assign addresses in seemingly overlapping ranges depending on the linker configuration.
+===== Creating ROM files =====
+Both the GameTankEmulator and GameTankFlashingOverhauled will assume a file with a size of exactly 2^21 bytes is a ROM file for the 2MB flash cartridge. In this file all of the banks are concatenated together in the order of their bank number, including empty banks.
+GameTankFlashingOverhauled will also treat any 16384-byte file with an extension like .bankXX (where XX is a hexadecimal number) as a single bank from the flashcart so that less time can be spent flashing empty banks.