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72 lines
2.6 KiB
Kotlin
72 lines
2.6 KiB
Kotlin
package razorvine.ksim65
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import razorvine.ksim65.components.*
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/**
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* The system bus that connects all other components together.
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* Usually, there is just a single Bus present.
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*
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* It distributes reset and clock signals to every connected component.
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* Data bytes can be read from the bus or written to the bus. It's distributed to the corresponding component(s).
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*
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* NOTE: currently the bus address mapping is STATIC: there is no possibility for Bank-switching.
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* (such as what the C-64 has; the ability to swap ROMs in and out of the address space).
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*/
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open class Bus {
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private val allComponents = mutableListOf<BusComponent>()
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private val memComponents = mutableListOf<MemMappedComponent>()
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fun reset() = allComponents.forEach { it.reset() }
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fun clock() = allComponents.forEach { it.clock() }
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operator fun plusAssign(memComponent: MemMappedComponent) = add(memComponent)
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operator fun plusAssign(component: BusComponent) = add(component)
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operator fun get(address: Address): UByte = read(address)
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operator fun set(address: Address, data: UByte) = write(address, data)
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fun add(component: BusComponent) {
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allComponents.add(component)
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component.bus = this
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}
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fun add(memComponent: MemMappedComponent) {
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memComponents.add(memComponent)
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allComponents.add(memComponent)
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memComponent.bus = this
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}
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/**
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* Read a data byte at the given address.
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* The first registered memory mapped component that listens to that address, will respond.
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* If no component is available, some CPUs generate a BUS ERROR but we return 0xff instead.
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*/
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open fun read(address: Address): UByte {
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memComponents.forEach {
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if (address >= it.startAddress && address <= it.endAddress) {
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val data = it[address - it.startAddress]
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require(data in 0..255) { "data at address $address must be a byte 0..255, but is $data" }
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return data
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}
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}
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return 0xff
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}
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/**
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* Write a data byte to the given address.
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* All memory mapped components that are mapped to the address, will receive the data.
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*/
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open fun write(address: Address, data: UByte) {
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require(data in 0..255) { "data written to address $address must be a byte 0..255" }
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memComponents.forEach {
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if (address >= it.startAddress && address <= it.endAddress)
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it[address-it.startAddress] = data
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}
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}
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fun memoryComponentFor(address: Address) =
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memComponents.first { it is MemoryComponent && address >= it.startAddress && address <= it.endAddress } as MemoryComponent
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}
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