Meownitor: monitor routine for System on Cat

Inspired by the monitor routine for 16-bit THINPAD.

Features

• All the features the 16-bit THINPAD monitor has.
• An optional timer that can report the time used by a user process when it terminates and kill it when it runs out of time.
• The optional choice of using the IRQ mechanism for serial inputting.
• Optional environment calls that allow user processes to send requests to and receive responses from the monitor.

Prerequisites

• 32-bit RISC-V GNU toolchain
• GNU make

Build

Bare mainbody:

make CFLAGS=   

With interrupt functionalities:

make CFLAGS="-DWITH_CSR -DWITH_INTERRUPT"

With interrupt and environment call (system call) functionalities:

make CFLAGS="-DWITH_CSR -DWITH_INTERRUPT -DWITH_ECALL"

With interrupt and IRQ functionalities:

make CFLAGS="-DWITH_CSR -DWITH_INTERRUPT -DWITH_IRQ"

With full functionalities:

make

To create an image bootable.bin with BootedCat that can be booted by System on Cat with MasterCat:

make START_ADR=<where to put it in memory> bootable.bin

Notes

• Most arch-dependent configurations are placed in arch.h. You may modify it according to the architecture of your target platform if you are not building it for System on Cat.
• All input integers (including immediates and register ids) must be in the hexadecimal form with prefix 0x. Spaces shall be used to separate the operands (no comma).
• All input letters are case-sensitive. Input instructions must be lowercased.
• The user process is invoked with the return address placed in register ra (x1) and could therefore exit with jalr zero, ra, 0. If environment call functionalities are available, a user process may also exit by sending an exit environment call.
• Environment calls:
  • Request code in a1, return value in a0, arguments in a2, a3, ...
  • Requests:
    • exit: exit the process and return to the monitor (a1 = 0)
    • putchar: write a character to the serial port (a1 = 1, character in a2)
    • getchar: read a character from the serial port (a1 = 2, result in a0)