cpubus

Documentation

Overview

Package cpubus defines the operations, addresses and symbols that are required by the CPU when reading/writing to memory.

Another way to think of this is: the operations, etc. that are required to interface with the VCS memory from the perspective of the CPU.

Index

• Constants
• Variables
• type Memory
• type Register

Constants

const BRK = uint16(0xfffe)

BRK is the address where the interrupt address is stored.

const NMI = uint16(0xfffa)

NMI is the address where the non-maskable interrupt address is stored.

const Reset = uint16(0xfffc)

Reset is the address where the reset address is stored.

Variables

var AddressError = errors.New("inaccessible address")

sentinal error returned by memory package functions

var RIOTReadSymbols = map[uint16]Register{

	0x0280: SWCHA,
	0x0281: SWACNT,
	0x0282: SWCHB,
	0x0283: SWBCNT,
	0x0284: INTIM,
	0x0285: TIMINT,
}

RIOTReadSymbols indexes all RIOT read symbols by normalised address.

var RIOTWriteSymbols = map[uint16]Register{
	0x0280: SWCHA,
	0x0281: SWACNT,
	0x0282: SWCHB,
	0x0283: SWBCNT,

	0x0294: TIM1T,
	0x0295: TIM8T,
	0x0296: TIM64T,
	0x0297: T1024T,
}

RIOTWriteSymbols indexes all RIOT write symbols by normalised address.

var Read []Register

Read is a sparse array containing the canonical labels for all read addresses.

If the address has no symbol then the entry will contain NotACPUBusRegister.

var ReadAddress = map[Register]uint16{}

ReadAddress indexes all VCS read addresses by canonical symbol.

var TIAReadSymbols = map[uint16]Register{

	0x00: CXM0P,
	0x01: CXM1P,
	0x02: CXP0FB,
	0x03: CXP1FB,
	0x04: CXM0FB,
	0x05: CXM1FB,
	0x06: CXBLPF,
	0x07: CXPPMM,
	0x08: INPT0,
	0x09: INPT1,
	0x0a: INPT2,
	0x0b: INPT3,
	0x0c: INPT4,
	0x0d: INPT5,
}

TIAReadSymbols indexes all TIA read symbols by normalised address.

var TIAWriteSymbols = map[uint16]Register{
	0x00: VSYNC,
	0x01: VBLANK,
	0x02: WSYNC,
	0x03: RSYNC,
	0x04: NUSIZ0,
	0x05: NUSIZ1,
	0x06: COLUP0,
	0x07: COLUP1,
	0x08: COLUPF,
	0x09: COLUBK,
	0x0a: CTRLPF,
	0x0b: REFP0,
	0x0c: REFP1,
	0x0d: PF0,
	0x0e: PF1,
	0x0f: PF2,
	0x10: RESP0,
	0x11: RESP1,
	0x12: RESM0,
	0x13: RESM1,
	0x14: RESBL,
	0x15: AUDC0,
	0x16: AUDC1,
	0x17: AUDF0,
	0x18: AUDF1,
	0x19: AUDV0,
	0x1a: AUDV1,
	0x1b: GRP0,
	0x1c: GRP1,
	0x1d: ENAM0,
	0x1e: ENAM1,
	0x1f: ENABL,
	0x20: HMP0,
	0x21: HMP1,
	0x22: HMM0,
	0x23: HMM1,
	0x24: HMBL,
	0x25: VDELP0,
	0x26: VDELP1,
	0x27: VDELBL,
	0x28: RESMP0,
	0x29: RESMP1,
	0x2a: HMOVE,
	0x2b: HMCLR,
	0x2c: CXCLR,
}

TIAWriteSymbols indexes all TIA write symbols by normalised address.

var Write []Register

Write is a sparse array containing the canonical labels for all write addresses.

If the address has no symbol then the entry will contain NotACPUBusRegister.

var WriteAddress = map[Register]uint16{}

WriteAddress indexes all VCS write addresses by canonical symbol.

Types

type Memory

type Memory interface {
	Read(address uint16) (uint8, error)
	Write(address uint16, data uint8) error
}

Memory defines the operations for the memory system when accessed from the CPU All memory areas implement this interface because they are all accessible from the CPU (compare to ChipBus). The VCSMemory type also implements this interface and maps the read/write address to the correct memory area -- meaning that CPU access need not care which part of memory it is writing to

Addresses should be mapped to their primary mirror in all cases.

In the case of cartridge implementations there should be no real distinction between Read and Write. This is because there is no R/W line to the cartridge. In the event that a cartridge has a RAM area, writing to the RAM is usually done through specific addreses.

type Register

type Register string

Register represents a named address in RIOT/TIA memory.

const (
	CXM0P  Register = "CXM0P"
	CXM1P  Register = "CXM1P"
	CXP0FB Register = "CXP0FB"
	CXP1FB Register = "CXP1FB"
	CXM0FB Register = "CXM0FB"
	CXM1FB Register = "CXM1FB"
	CXBLPF Register = "CXBLPF"
	CXPPMM Register = "CXPPMM"
	INPT0  Register = "INPT0"
	INPT1  Register = "INPT1"
	INPT2  Register = "INPT2"
	INPT3  Register = "INPT3"
	INPT4  Register = "INPT4"
	INPT5  Register = "INPT5"
	SWCHA  Register = "SWCHA"
	SWACNT Register = "SWACNT"
	SWCHB  Register = "SWCHB"
	SWBCNT Register = "SWBCNT"
	INTIM  Register = "INTIM"
	TIMINT Register = "TIMINT"
	VSYNC  Register = "VSYNC"
	VBLANK Register = "VBLANK"
	WSYNC  Register = "WSYNC"
	RSYNC  Register = "RSYNC"
	NUSIZ0 Register = "NUSIZ0"
	NUSIZ1 Register = "NUSIZ1"
	COLUP0 Register = "COLUP0"
	COLUP1 Register = "COLUP1"
	COLUPF Register = "COLUPF"
	COLUBK Register = "COLUBK"
	CTRLPF Register = "CTRLPF"
	REFP0  Register = "REFP0"
	REFP1  Register = "REFP1"
	PF0    Register = "PF0"
	PF1    Register = "PF1"
	PF2    Register = "PF2"
	RESP0  Register = "RESP0"
	RESP1  Register = "RESP1"
	RESM0  Register = "RESM0"
	RESM1  Register = "RESM1"
	RESBL  Register = "RESBL"
	AUDC0  Register = "AUDC0"
	AUDC1  Register = "AUDC1"
	AUDF0  Register = "AUDF0"
	AUDF1  Register = "AUDF1"
	AUDV0  Register = "AUDV0"
	AUDV1  Register = "AUDV1"
	GRP0   Register = "GRP0"
	GRP1   Register = "GRP1"
	ENAM0  Register = "ENAM0"
	ENAM1  Register = "ENAM1"
	ENABL  Register = "ENABL"
	HMP0   Register = "HMP0"
	HMP1   Register = "HMP1"
	HMM0   Register = "HMM0"
	HMM1   Register = "HMM1"
	HMBL   Register = "HMBL"
	VDELP0 Register = "VDELP0"
	VDELP1 Register = "VDELP1"
	VDELBL Register = "VDELBL"
	RESMP0 Register = "RESMP0"
	RESMP1 Register = "RESMP1"
	HMOVE  Register = "HMOVE"
	HMCLR  Register = "HMCLR"
	CXCLR  Register = "CXCLR"
	TIM1T  Register = "TIM1T"
	TIM8T  Register = "TIM8T"
	TIM64T Register = "TIM64T"
	T1024T Register = "T1024T"
)

List of Valid CPUBusRegister values.

const NotACPUBusRegister Register = ""

Address does not correspond with any known symbol.