91 lines
2.7 KiB
Markdown
91 lines
2.7 KiB
Markdown
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---
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title: Callbacks
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weight: 5
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pre: ""
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chapter: false
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---
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## addEventCallback ##
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**Syntax**
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emu.addEventCallback(function, type)
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**Parameters**
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function - A Lua function.
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type - *Enum* See [eventType](/apireference/enums.html#eventtype).
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**Return value**
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Returns an integer value that can be used to remove the callback by calling [removeEventCallback](#removeeventcallback).
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**Description**
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Registers a callback function to be called whenever the specified event occurs.
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The callback function receives no parameters.
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## removeEventCallback ##
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**Syntax**
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emu.removeEventCallback(reference, type)
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**Parameters**
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reference - The value returned by the call to [addEventCallback](#addeventcallback).
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type - *Enum* See [eventType](/apireference/enums.html#eventtype).
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**Return value**
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*None*
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**Description**
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Removes a previously registered callback function.
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## addMemoryCallback ##
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**Syntax**
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emu.addMemoryCallback(function, type, startAddress, endAddress)
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**Parameters**
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function - A Lua function.
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type - *Enum* See [memCallbackType](/apireference/enums.html#memcallbacktype)
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startAddress - *Integer* Start of the CPU memory address range to register the callback on.
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endAddress - *Integer* End of the CPU memory address range to register the callback on.
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**Return value**
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Returns an integer value that can be used to remove the callback by calling [removeMemoryCallback](#removememorycallback).
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**Description**
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Registers a callback function to be called whenever the specified event occurs.
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The callback function receives 2 parameters `address` and `value` that correspond to the address being written to or read from, and the value that is being read/written.
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For reads, the callback is called *after* the read is performed.
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For writes, the callback is called *before* the write is performed.
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If the callback returns an integer value, it will replace the value -- you can alter the results of read/write operation using this. e.g:
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```lua
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function writeCallback(address, value)
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--This sets bit 0 to 0 for all CHR RAM writes
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return value & 0xFE
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end
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emu.addMemoryCallback(writeCallback, emu.memCallbackType.ppuWrite, 0, 0x1FFF)
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```
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## removeMemoryCallback ##
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**Syntax**
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emu.removeMemoryCallback(reference, type, startAddress, endAddress)
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**Parameters**
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reference - The value returned by the call to [addMemoryCallback](#addmemorycallback).
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type - *Enum* See [memCallbackType](/apireference/enums.html#memcallbacktype).
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startAddress - *Integer* Start of the CPU memory address range to unregister the callback from.
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endAddress - *Integer* End of the CPU memory address range to unregister the callback from.
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**Return value**
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*None*
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**Description**
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Removes a previously registered callback function.
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