Documentation
¶
Overview ¶
Package memory implements the Atari VCS memory model. The addresses and memory sub-packages help with this.
It is important to understand that memory is viewed differently by different parts of the VCS system. To help with this, the emulation uses what we call memory buses. These buses have nothing to do with the real hardware; they are purely conceptual and are implemented through Go interfaces.
The following ASCII diagram tries to show how the different components of the VCS are connected to the memory. What may not be clear from this diagram is that the peripheral bus only ever writes to memory. The other buses are bidirectional.
PERIPHERALS
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\/
periph bus
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\/
CPU ---- cpu bus ---- MEMORY ---- chip bus ---- TIA
\
| \
| \---- RIOT
debugger bus
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DEBUGGER
The memory itself is divided into areas, defined in the memorymap package. Removing the periph bus and debugger bus from the picture, the above diagram with memory areas added is as follows:
==== TIA ---- chip bus ---- TIA
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|==== RIOT ---- chip bus ---- RIOT
CPU ---- cpu bus ---- *
|==== PIA RAM
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==== Cartridge
The asterisk indicates that addresses used by the CPU are mapped to the primary address. The memorymap package contains more detail on this.
Note that the RIOT registers and PIA RAM are all part of the same hardware package, the PIA 6532. However, for our purposes the two memory areas are considered to be entirely separate.
Index ¶
- type ChipMemory
- func (area *ChipMemory) ChipRead() (bool, bus.ChipData)
- func (area *ChipMemory) ChipWrite(reg addresses.ChipRegister, data uint8)
- func (area *ChipMemory) InputDeviceWrite(reg addresses.ChipRegister, data uint8, preserveBits uint8)
- func (area *ChipMemory) LastReadRegister() string
- func (area ChipMemory) Peek(address uint16) (uint8, error)
- func (area ChipMemory) Poke(address uint16, value uint8) error
- func (area *ChipMemory) Read(address uint16) (uint8, error)
- func (area *ChipMemory) Write(address uint16, data uint8) error
- type RAM
- type VCSMemory
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type ChipMemory ¶
type ChipMemory struct {
bus.DebuggerBus
bus.ChipBus
bus.CPUBus
bus.InputDeviceBus
// contains filtered or unexported fields
}
ChipMemory defines the information for and operations allowed for those memory areas accessed by the VCS chips as well as the CPU
func (*ChipMemory) ChipRead ¶
func (area *ChipMemory) ChipRead() (bool, bus.ChipData)
ChipRead is an implementation of memory.ChipBus
func (*ChipMemory) ChipWrite ¶
func (area *ChipMemory) ChipWrite(reg addresses.ChipRegister, data uint8)
ChipWrite is an implementation of memory.ChipBus
func (*ChipMemory) InputDeviceWrite ¶
func (area *ChipMemory) InputDeviceWrite(reg addresses.ChipRegister, data uint8, preserveBits uint8)
InputDeviceWrite implements memory.InputDeviceBus
func (*ChipMemory) LastReadRegister ¶
func (area *ChipMemory) LastReadRegister() string
LastReadRegister is an implementation of memory.ChipBus
func (ChipMemory) Peek ¶
func (area ChipMemory) Peek(address uint16) (uint8, error)
Peek is an implementation of memory.DebuggerBus. Address must be normalised.
func (ChipMemory) Poke ¶
func (area ChipMemory) Poke(address uint16, value uint8) error
Poke is an implementation of memory.DebuggerBus. Address must be normalised.
type RAM ¶
type RAM struct {
bus.DebuggerBus
bus.CPUBus
// contains filtered or unexported fields
}
RAM represents the 128bytes of RAM in the PIA 6532 chip, found in the Atari VCS.
type VCSMemory ¶
type VCSMemory struct {
bus.CPUBus
// memmap is a hash for every address in the VCS address space, returning
// one of the four memory areas
Memmap []bus.DebuggerBus
// the four memory areas
RIOT *ChipMemory
TIA *ChipMemory
RAM *RAM
Cart *cartridge.Cartridge
// the following are only used by the debugging interface. it would be
// lovely to remove these for non-debugging emulation but there's not much
// impact on performance so they can stay for now:
//
// . a note of the last (mapped) memory address to be accessed
// . the value that was written/read from the last address accessed
// . whether the last addres accessed was written or read
// . the ID of the last memory access (currently a timestamp)
LastAccessAddress uint16
LastAccessValue uint8
LastAccessWrite bool
LastAccessID int
// contains filtered or unexported fields
}
VCSMemory is the monolithic representation of the memory in 2600.
func NewVCSMemory ¶
NewVCSMemory is the preferred method of initialisation for VCSMemory
func (*VCSMemory) Read ¶
Read is an implementation of CPUBus. Address will be normalised and processed by the correct memory area.
func (*VCSMemory) ReadZeroPage ¶
ReadZeroPage is an implementation of CPUBus. Address will be normalised and processed by the correct memory areas.
Source Files
Directories
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| Path | Synopsis |
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Package addresses countains all information about VCS addresses and registers, including canonical symbols for read and write addresses and registers.
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Package addresses countains all information about VCS addresses and registers, including canonical symbols for read and write addresses and registers. |
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Package bus defines the memory bus concept.
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Package bus defines the memory bus concept. |
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Package cartridge fully implements loading of mapping of cartridge memory.
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Package cartridge fully implements loading of mapping of cartridge memory. |
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Package memorymap facilitates the translation of addresses to primary address equivalents.
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Package memorymap facilitates the translation of addresses to primary address equivalents. |