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forgot to checkin the bus changes for memory mapping

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This commit is contained in:
Irmen de Jong 2020-02-05 01:27:04 +01:00
parent 8b84a7c653
commit b3334a23b9
1 changed files with 29 additions and 12 deletions
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41
src/main/kotlin/razorvine/c64emu/Bus6510.kt
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@ -5,13 +5,13 @@ import razorvine.ksim65.components.Rom
import razorvine.ksim65.components.UByte
/**
* The C64's bus is a bit peculiar
* Appearance of RAM or ROM in certain adress ranges can be dynamically controlled
* via the 6510's IO port register in $00/$01
* We only implement banking in or out the character rom or I/O space at $d000-$e000 for now.
* Doing it here in the bus directly is the poor man's mmu solution, I guess
* The C64's bus is a bit peculiar:
* appearance of RAM or ROM in certain address ranges can be dynamically controlled
* via the 6510's IO port register in $00/$01, "bank switching".
* More info here https://www.c64-wiki.com/wiki/Bank_Switching
*
* TODO: mapping the RAM/ROMs in and out of the other banks in the address space (controlled by loram and hiram).
* Note: we don't implement the expansion port's _EXROM and _GAME lines that are used
* for mapping in cartridge ROMs into the address space.
*/
class Bus6510(private val ioPort: CpuIoPort,
private val chargen: Rom,
@ -19,13 +19,30 @@ class Bus6510(private val ioPort: CpuIoPort,
private val kernal: Rom): razorvine.ksim65.Bus() {
override fun read(address: Address): UByte {
if(address in 0xd000..0xe000) {
if(!ioPort.charen) {
// character rom is enabled in this address range (instead of I/O)
return chargen[address-chargen.startAddress]
return when(address) {
in 0x0000..0x9fff -> super.read(address) // always RAM
in 0xa000..0xbfff -> {
// BASIC or RAM
if(ioPort.loram && ioPort.hiram)
basic[address - 0xa000]
else
super.read(address)
}
in 0xc000..0xcfff -> super.read(address) // always RAM
in 0xd000..0xdfff -> {
// IO or CHAR ROM
if(ioPort.charen)
super.read(address)
else
chargen[address - 0xd000]
}
else -> {
// 0xe000..0xffff, KERNAL or RAM
if(ioPort.hiram)
kernal[address - 0xe000]
else
super.read(address)
}
}
return super.read(address)
}
}