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jor1k is an OR1K emulator written in JavaScrip running Linux. It runs in common web browser.
Download the content from the repisotory and open jor1k.html in your browser. Currently the program is tested under following browsers
- Firefox 17
- Opera 12
- Google Chrome 23 (if running locally you have to run the browser with the command --disable-web-security)
- Safari under iOS: works but no keyboard input
- Safari 5: Boots but hangs after the unpacking of initramfs (no Uint8ClampedArray support)
- Internet Explorer: not working
- 32-Bit OR1000 Emulator with MMU, TICK counter and PIC ( or1k specification )
- 32 MB Ram
- UART 16550
- ocfb Framebuffer 320x240 32bpp
- Linux Terminal Emulator
- 5 MB image running Linux 3.1 and busybox 1.19 (and much more)
- 0x00000000 - 0x02000000 32 MB Random Access Memory
- 0x90000000 - 0x90000006 UART 16550 connected to the terminal and keyboard
- 0x91000000 - 0x91001000 opencore VGA/LCD 2.0 core frame buffer (320x200 32bpp)
- 0x92000000 - 0x92001000 Ethernet MAC controller (not working, just for compatibility)
The machine is big endian machine, but the typed array from Javascript work with little endian. Most of the memory accesses are 32 Bit. So at the beginning, after loading the image every 32-Bit word is swapped and 8 and 16 Bit memory accesses are treated in a special way.
Javascript normally does have predefined types. To cast to unsigned and signed values one can use the (number>>>0) and (number>>0) modifier, which does only change the type of "number".
Sometimes a few number must be sign extended. This is done efficiently by the command (number<<x)>>x, where x is an appropriate shift value. To sign extend an 8 bit value to a 32 bit value the command is ((number<<24)>>24).
Most of the time the whole instruction fetch is done very efficiently with the command
if (!((oldpc^this.pc)&0xFFFFE000)) { oldpc = this.pc; ins = uint32mem[(this.instlb^oldpc)>>>2]; } else ...
The important trick is first to check if the current page is still valid and if this is the case just to xor the program counter. This can fail if the tlb of this page is changed while being on the same page.
The TLB Refill is done in Javascript. Unfortunately this makes it dependent on the Linux kernel as it needs the pointer to the internal translation table of the Linux kernel.
- separating and cleanup code
- Include ATA emulation to simulate a drive, to have more space for programs which will be loaded on demand from the web server
- Add scripts in the repository to create this drive image.
- Running a C64 Emulator on the machine with the game Zork. Then I have the emulation chain x86 -> JavaScript -> or1k -> MOS6502 -> Z-Machine
- Running a small X-server in the framebuffer. Add touch screen input.
- Run Ethernet over the server.
- Speed up the whole emulation.
Sebastian Macke simulationcorner.net