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n00bROM

n00bROM is an open source custom firmware for use in PS1 cheat devices or generic homebrew cartridges that connect to the expansion port found in SCPH-750x and older models. Functionality wise, n00bROM is similar to Caetla in that it allows uploading and executing PS-EXEs on the console, ideal for testing PS1 programs on real hardware in homebrew development or ROM hacking.

Whilst n00bROM is fairly bare bones compared to Caetla and is more developer oriented, n00bROM makes up for it by featuring capabilities not found in vanilla Caetla; such as PS-EXE download via serial, serial TTY, supporting more EEPROMs, built-in flash option for quick updating, nocash unlock and simplified swap trick boot options.

While n00bROM may be used to boot backups, copies or whatever you want to call it, this is NOT the main purpose of n00bROM. n00bROM is primarily intended as a tool for homebrew development and getting homebrew to run on real hardware, supported by the fact it has mostly developer oriented features and lacks any sort of cheat functionality (and before you ask, this will not be implemented). It is entirely up to the user how they use n00bROM as they see fit, Lameguy64 is not responsible nor concerned of any liabilities it may bring from the use of n00bROM, if such accusations ever do happen. If you don't feel comfortable using n00bROM, do not use n00bROM.

Selling of cheat devices with n00bROM pre-flashed is highly discouraged however.

Features

  • Automatic and manual video standard selection.

  • Chipless CD-R boot capabilities; nocash unlock and simplified swap trick. It may not bypass region locked (internal lock, not by BIOS or CD-ROM) or libcrypt protected games however.

  • Bypasses BIOS shell entirely, shortening boot times and bypasses pesky license data checks (such as PS logo data) found in some BIOS revisions, allowing to boot imports and eliminates the need to patch disc images.

  • Can boot completely unlicensed discs provided there is a SYSTEM.CNF or PSX.EXE file is present in the root.

  • PS-EXE loader capability via serial or Xplorer parallel port interface. Uses mcomms/liteload style protocol for the serial loader.

  • TTY redirection via serial or Xplorer parallel port for both stdin and stdout text streams. Use mcomms in -term mode or any serial terminal program when using serial TTY.

  • Access files from host system via the PCDRV interface (Xplorer only). Create, read and write operations are implemented with parity checking and checksums for improved reliability. Directory query and changing current directories are also supported (use BIOS file functions, does not support libsn style PCDRV calls by special break opcodes)

  • Exception handler for visually trapping software crashes.

  • Supports more EEPROMs than Caetla with EEPROM ID and work-in-progress cartridge ID capabilities.

  • Built-in EEPROM flasher for updating n00bROM easily.

  • Animated plasma and SMPTE color bar backgrounds.

  • Small ROM size; just under 32KB.

  • Written entirely in MIPS assembly!

Usage

n00bROM is fairly straight forward to use. Pressing START from the 'home' screen will initiate the CD-ROM boot sequence and pressing SELECT will bring up the ROM menu, where you can configure n00bROM to your liking.

Whilst in the home screen, n00bROM will constantly listen for any PS-EXE or binary uploads from the serial interface. If Cartridge Type is set to Xplorer in the ROM menu, it will additionally listen for uploads from the parallel port interface on the cartridge. However, it is not compatible with catflap, so you'll have to use the included xpcomms tool instead.

For serial uploads, you'll have to use mcomms to upload your PS-EXE to the serial interface ( https://github.com/lameguy64/mcomms ). It behaves more or less like running LITELOAD on the target console.

Entering the ROM menu, the options available are as follows:

Video standard:

Specifies the video standard n00bROM will use. Available options are Auto, NTSC and PAL. This option does not affect the video standard games will use.

Auto works by checking the SCEx string within the BIOS ROM to identify the system's region.

CD-ROM Boot Mode:

Specifies the boot method that will be used as part of the CD-ROM boot sequence, when pressing START from the 'home' screen or enabling Quick Boot. This option also takes effect when uploading a PS-EXE to the console, in between download completion and transferring execution to the PS-EXE. Available options are Normal, Unlock and EZ-Swap.

Unlock allows regular CD-ROMs, CD-Rs and imports to become readable and bootable without a mod-chip. This works by issuing 'secret' backdoor commands to the CD-ROM controller which enables reading of data sectors from unlicensed or out of region discs. This option only works for US, EU and Yaroze consoles. ( http://problemkaputt.de/psx-spx.htm#cdromsecretunlockcommands )

EZ-Swap allows reading and booting CD-Rs by allowing a swap trick to be performed easily, as it stops the disc during the swap procedure to allow for swapping without the risk of damaging the disc or console. As of 0.28b, games and homebrew that use CD Audio will work properly by issuing a SetSession command to reload the ToC without clearing the authentication state, though accessing newer sessions in a multi-session disc is not possible. Obviously, an official copy of a game that matches the console's region is required for this procedure. This option may seem redundant as Uunlock is the better overall option, but this is here for Japan region consoles which do not support Unlock.

TTY Interface:

Specifies which interface to direct TTY access (ie. printf() output and getchar()/gets() input). Available options are Off, Serial and Xplorer.

Serial directs TTY to the Serial I/O port of the console at 115200 baud, 8 data bits, 1 stop bit, no parity and no handshaking. Pending input can be polled through ioctl(0, FIOCSCAN, 0), or ioctl(0, (('f'<<8)|2), 0) if FIOCSCAN is not available.

Xplorer directs TTY to the parallel port interface on the Xplorer cartridge. It is currently not very reliable to get working with software booted from CD-ROM, such as games however.

PCDRV (Xplorer only):

When enabled, n00bROM will install a special PCDRV device into the BIOS kernel, which can be used to access files directly from the host system using standard BIOS file functions. No special library or headers required to take advantage of this feature.

This is akin to the pcdrv: device found in Caetla and official PS1 development environments. PCDRV access by break opcodes (ie. libsn.h) are not supported however.

xpcomms must be running on the host PC, to serve as the file server for PCDRV functionality.

Exception:

When enabled, n00bROM will patch a hook to the BIOS function vector, trapping unhandled exceptions (SystemErrorUnresolvedException - A(40h)) that displays a killscreen showing all relevant processor registers and stack values of when the unhandled exception occured (ie. reserved opcodes, invalid/misaligned memory address break opcodes, etc), useful for identifying software crashes without an interactive debugger.

This option may be removed in future versions of n00bROM, as the new BIOS function vector method is less likely to introduce compatibility issues, unlike the old method which patches a hook to the exception vector which can introduce compatibility problems.

n00bROM also hooks a killscreen routine for boot failures (SystemErrorBootOrDiskFailure - A(A1h)) which cannot be disabled, a leftover from testing the new BIOS based bootstrap method. This is still useful for discriminating from a software crash after booting, or a disc error during booting.

Cartridge Type:

Specifies the type of cartridge n00bROM has been flashed on. This is only really used for which switch detection logic to use, which is handled differently between PAR/GS and Xplorer cartridges. Available options are Generic (for carts without a switch, or a custom cart that is not supported yet), PAR/GS and Xplorer. Make sure you choose the correct option as otherwise you may render n00bROM unbootable on your cartridge by setting the wrong cartriddge type.

Setting Xplorer also enables PS-EXE and binary downloads from the parallel port interface, using the included xpcomms tool.

OFF Switch Action:

Specifies what action n00bROM will take if the switch on the cartridge has been set to the OFF position. Available options are BIOS and Quick Boot. This option only works if Cartridge Type is set to PAR/GS or Xplorer.

BIOS would simply skip starting n00bROM, and the console will behave as if no cartridge was inserted. All n00bROM features are also disabled.

Quick boot simply bypasses the shell and jumps straight to the bootstrap sequence. TTY, Exception and PCDRV hooks are also set when enabled. The CD-ROM Boot Mode option also takes effect for this mode.

Background:

Specifies the background image to display. Available options are Plasma and SMPTE color bars. The latter will feel right at home with the official development boards.

More backgrounds may be added in the future, if ROM space allows for such bells and whistles to be implemented.

Home screen:

Specifies the type of home screen to be displayed in the 'home' screen, shown when starting n00bROM. Available options are Banner, Minimal and BG Only.

Banner displays the large banner with a fairly long notice text.

Minimal only displays a small box that shows some information about n00bROM and enabled configuration settings such as STTY (serial TTY), XTTY (Xplorer TTY), XPDL (Xplorer Download), Exception and PCDRV.

BG Only, as the name suggests, only displays the background. This also disables the screen dimming, so it can be used in combination with the SMPTE background option for testing/calibrating video equipment.

Flash Mode:

Enters Flash Mode for updating or replacing n00bROM. n00bROM can only flash the first 128K currently. The Flash Mode option will not work if the EEPROM is ID'd as an unknown chip.

Save Settings:

Saves configuration setting you have changed to the EEPROM. This option will not work if the EEPROM is ID'd as an unknown chip.

Supported EEPROMs

The following lists EEPROMs n00bROM may support writing to when saving settings or using the built-in flash capability. These chips are also the most commonly used among various cheat devices, apart from the Cypress one.

Atmel: AT29C020 AT29BV020 AT29C040A AT29LV010A AT29xV040A

SST: 29EE010 29xE010 29EE010A 29xE010A 29EE020 29xE020 29EE020A 2xEE020A 28SF040

Winbond: W29EE01x W29C020 W29C040

Cypress: S29A1016J

Chips that n00bROM has been most tested with are SST 29EE020 and Winbond W29C020. All other chips listed above are untested, but should work in theory.

More chips may be added by adding appropriate entries to the chipid_list in tables.inc, but keep in mind that n00bROM only supports writing using the standard JEDEC method, with software data protection commands (issues a software data protect enable command then immediately writes a page worth of bytes to the EEPROM).

Building

Building n00bROM requires Kingcom's armips assembler ( https://github.com/kingcom/armips ).

Building the ROM itself is just a matter of running build.sh under Linux with a bash prompt or build.bat under Windows. It should produce romhead.bin, ramprog.bin and n00brom.rom alongside the associated symbol/listing files.

Installing

Currently, the only feasible way to flash a ROM to a cheat cartridge is by either desoldering the EEPROM and flashing the chip with an EEPROM programmer, or using a really old tool called X-Flash, which requires manual preparation of the disc in a specific manner and requires a chipped console to actually get it to boot.

To help remedy this problem, a new flash utility made using PSn00bSDK is in the works, and will support downloading ROM images from serial and reading multi-session discs, so CD-Rs will be wasted less and to make installing new versions of n00bROM easier.

Credits

Main developer: Lameguy64

Reference used: nocash's PlayStation specs document ( http://problemkaputt.de/psx-spx.htm )

nicolasnoble's PS1 openbios reverse engineering project: ( https://github.com/grumpycoders/pcsx-redux/tree/master/src/mips/openbios )

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Open-source Caetla equivalent for PS1 homebrew development

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