System Call Functionality

You can use the system call functionality in the picoJava^TM environment to extend the capabilities of the simulation environment in various ways. A sample implementation of the system call functionality is present in the picoJava-II distribution. See the README in the directory $PICOJAVAHOME/$PROJECT/syscall_example.

At startup, IAS or RTL looks for a dynamically linked library in the file that the environment variable PICOJAVA_SYSCALL_LIB points to. The following process follows:

• If PICOJAVA_SYSCALL_LIB is not set, IAS or RTL drops the system call functionality.
• If IAS or RTL finds PICOJAVA_SYSCALL_LIB, it then looks for the functions picojava_syscall_init () and picojava_syscall () in the library.
  • If either of these functions is absent, then IAS or RTL prints an error message and quits.
  • If both functions are present, then IAS or RTL calls the function int picojava_syscall_init ().

    If int picojava_syscall_init () returns a nonzero value, IAS or RTL assumes that initialization has succeeded and enables the system call functionality; otherwise, it assumes that initialization failed and disables the functionality.

    The initialization function cannot assume any state, except that IAS or RTL has created memory (by calling cmInit) and initialized it--that is, IAS or RTL does not write over anything that is now written.

To invoke system calls, the program that runs on IAS or RTL must write to the special address 0xffe8 with the ncstore_byte instruction. Doing so triggers a call to the function void picojava_syscall (). The IAS or RTL environment does not handle passing of parameters between the code that runs on the picoJava core and the system call library; instead, IAS or RTL assumes that parameters and such are set up in memory according to a predefined protocol.

Compile with this command:

cc -G -o libsyscall.so.1 libsyscall.c

If you are using gcc, use this command:

gcc -fpic -shared -o libsyscall.so.1 libsyscall.c

Set up the environment variable, as follows

setenv PJSIM_SYSCALL_LIB libsyscall.so.1

IAS or RTL looks for PJSIM_SYSCALL_LIB; if it is set, it the loads the functions from the specified library.