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+LibPSn00b Example Programs
+Part of the PSn00bSDK Poject
+
+TurboBoot Example by Lameguy64
+
+
+Explanation:
+
+This example demonstrates how to create a ROM program to be used on a cheat
+cartridge such as an Action Replay or Xplorer using GNU assembler. The program
+stored in ROM is executed pretty much instantly on power-on.
+
+The PS1 BIOS can execute code from a ROM chip connected to the expansion port
+(or Parallel I/O port) such as a cheat cartridge provided the valid headers
+are present. However, the boot vectors are somewhat limited as it only
+provides a preboot vector and a postboot vector.
+
+The preboot vector is executed at the earliest point of the BIOS start-up
+sequence which means the RAM is almost completely blank and you can't execute
+PS-EXEs from this point whearas the postboot vector is only executed between
+the PS logo and game execution. To get around this limitation, the preboot
+vector is used to execute code that places a breakpoint to a desired point
+in memory and returns execution to the BIOS. This will effectively intercept
+execution once it reaches the breakpoint allowing to run code from ROM with
+an initialized kernel allowing for bootstrapping PS-EXEs from ROM, CD or
+from a comms interface such as serial.
+
+The Xplorer and later Pro Action Replay cheat devices use this so called
+'midboot' trick in their firmwares.
+
+In this TurboBoot example, the ROM program attempts to boot a PS-EXE from
+CD using BIOS CD-ROM and file functions. It will also parse through the
+SYSTEM.CNF to retrieve the file name of executable as well as some boot
+parameters such as stack addres and number of TCBs and EvCBs. The ROM
+program can fallback to attempting to load a PS-EXE named PSX.EXE if the
+SYSTEM.CNF file does not exist like in the official BIOS.
+
+This example can also be used as a turbo boot utility as it boots straight
+to the game, skipping the start-up animation altogether. It cannot be used
+as a way to bypass the authentication check of an unmodified console however
+(though it would help with bypassing the license data check on older Japanese
+consoles) as the CD-ROM would only read data discs correctly IF the elusive
+wobble groove containing the SCE string of the disc is present or when a
+modchip is installed. It is possible to circumvent this by issuing special
+'CD Unlock' commands (see nocash's psx-spx document) to the CD-ROM controller
+which would effectively turn this into a chipless modchip solution that plugs
+to the expansion port. However, the unlock commands only works on US and EU
+consoles.
+
+It is possible and pretty trivial to boot a PS-EXE straight from ROM by
+simply copying the program text from ROM to its desired location in RAM and
+transferring execution to it. Such an example may be created in the future.
+
+This ROM program example had to be written entirely in assembly as C cannot
+be used to write a ROM program even though it should be possible with some
+assembly code to take care of the bootstrapping. GNU ld would complain about
+'relocation truncation of R_MIPS_GPREL16' when you map program text to ROM
+starting at 0x1f000000 (EXP ROM segment) and program data and bss sections
+to RAM. Unknown how to get around this as all methods I've tried so far
+either don't work or it just produces a massive binary file.
+
+
+Building:
+
+To build this example, simply run make and a file named cartrom.rom should
+be created. Run the ROM in no$psx (make sure a ISO image has been opened
+first) or burn it to an Xplorer/PAR EEPROM (I recommend modding a PAR with
+a DIP32 socket if you wish to program the chip externally which in many
+cases would be easier).
+
+
+Changelog:
+
+May 23, 2019 - Initial version.