apple2js/js/ram.ts

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/* Copyright 2010-2019 Will Scullin <scullin@scullinsteel.com>
*
* Permission to use, copy, modify, distribute, and sell this software and its
* documentation for any purpose is hereby granted without fee, provided that
* the above copyright notice appear in all copies and that both that
* copyright notice and this permission notice appear in supporting
* documentation. No representations are made about the suitability of this
* software for any purpose. It is provided "as is" without express or
* implied warranty.
*/
import { byte, memory, Memory, Restorable } from './types';
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import { allocMemPages } from './util';
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export interface RAMState {
/** Copy of contents. */
mem: memory;
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}
/**
* Represents RAM from the start page `sp` to end page `ep`. The memory
* is addressed by `page` and `offset`.
*/
export default class RAM implements Memory, Restorable<RAMState> {
private start_page: byte;
private end_page: byte;
private mem: memory;
constructor(sp: byte, ep: byte) {
this.start_page = sp;
this.end_page = ep;
this.mem = allocMemPages(ep - sp + 1);
}
public start(): byte {
return this.start_page;
}
public end(): byte {
return this.end_page;
}
public read(page: byte, offset: byte) {
return this.mem[(page - this.start_page) << 8 | offset];
}
public write(page: byte, offset: byte, val: byte) {
this.mem[(page - this.start_page) << 8 | offset] = val;
}
public getState(): RAMState {
return {
mem: new Uint8Array(this.mem)
};
}
public setState(state: RAMState) {
this.mem = new Uint8Array(state.mem);
}
}