Trap Handlers

NOTE: These docs will apply starting in 0.4.x. At time of writing, the current version is 0.3.60329 and these docs are not accurate.

What is the "Trap Handler"

Zarem utilizes "Trap Handlers" to take care of syscalls, traps, execptions, etc when in hosted emulation. The trap handler can be changed by modifying the TrapHost value under the emulator config in a .zrmp project file. If you remove the TrapHost entirely, the emulator will run as a fully emulated machine, where traps and exceptions will jump to trap/exception vector.

Built-in Trap Handlers

Zarem has a collection of provided trap handlers that can be selected from. This is primarily to retain backwards compatibility with other emulator systems. For new projects the Zarem Trap Handler is recommended.

Zarem Trap Handler

To use the Zarem trap handler, set the TrapHost value to Zarem.

Compatibility

This trap handler works with MIPS and RISC-V.

Architecture	ID Register	Argument Registers	Result registers	Float Arg Register	Float Result Register
MIPS	$v0	$a0 - $a2	$v0 - $v1	$f12	$f0
RISC-V	a7	a0 - a2	a0 - a1	f12	f0

Syscall Table

Operation	Syscall ID	Description	Arguments & Results
Print Integer	1	Prints an integer	arg0 - The integer to print
Read Integer	2	Reads an integer	ret0 - The integer read
Print String	3	Prints a null-terminated string	arg0 - Address of null-terminated string arg2 - The encoding of the string*
Read String	4	Reads a null-terminated string to an input buffer	arg0 - The buffer's address arg1 - The buffer's size arg2 - The encoding of the string*
Print Float	5	Prints a single-precision floating-point value	farg - The float to print
Read Float	6	Reads a single-precision floating-point value	fret - The float read
Print Double	7	Prints a double-precision floating-point value	farg - The double to print
Read Double	8	Reads a double-precision floating-point value	fret - The double read
Exit	9	Ends the program

*Encoding: 0-ascii, 1-utf8, 2-utf16

Custom trap handler

Not currently supported. Plug-in system in the works.