    SYSCALLS
    

Insert SYS instruction after setting the registers to make a system call.
    
  READ (AX == 0)

BX = pointer to buffer
CX = count of bytes to read
DX = file descriptor

Count of bytes read is returned in AX.

Equivalent to C function call fread(BX, 1, CX, DX);
  

  WRITE (AX == 1)

BX = pointer to buffer
CX = count of bytes to write
DX = file descriptor

Count of bytes written is returned in AX.

Equivalent to C function call fwrite(BX, 1, CX, DX);

  OPEN (AX == 2)
  
BX = file mode
CX = Permissions (not implemented)
DX = pointer to a string containing file name
EX = Pointer to a struct containing the file descriptor data (optional)

The file descriptor is returned in AX. Returns -1 (0xFFFF) on error.

Equivalent to C function call fopen(DX, BX);

FILE MODES

The default open mode is read-only (BX == 0).
If bit 0 is set (BX & 0x01), the file is truncated to zero length and opened
in write mode.
If bits 0 and 1 are set (BX & 0x02), the file is opened in append mode.

If bit 2 is set (BX & 0x04), the file is opened in read-write-mode. Bit 2 
represents the plus sign in C fopen()'s second argument string.

If bit 3 is set (BX & 0x08), the file is opened in unbuffered mode.

If bit 11 is set (BX & 0x1000), the stream is opened in non-blocking mode.

OPENING SYSTEM PORTS

Serial and parallel ports can be opened with OPEN syscall. Serial ports are
named COMn, where n is the port number starting from 1. Parallel ports are
named LPTn. Parallel ports are currently write-only. Serial ports are bi-
directional.

With system ports the BX register does not work the same way as with actual
files. If BL is non-zero when opening a parallel port, the printer (if any)
in that port is initialized to use automatic newline. With serial ports the
workings of the BX register are described below.

The lowest 4 bits in the BH register represent the baud rate as shown
below:

0       == 50 baud
1       == 110 baud
2       == 150 baud
3       == 300 baud
4       == 600 baud
5       == 1200 baud
6       == 2400 baud
7       == 4800 baud
8       == 9600 baud
9       == 19200 baud
10      == 38400 baud
11      == 57600 baud
12      == 115200 baud

The upmost two bytes in the BH register select what flow control to use.
0b00 means no flow control, 0b01 means XON/XOFF and 0b10 means RTS/CTS.

Bits 0-1 in BL register are used to select word length.
0b00 = 5 bit,
0b01 = 6 bit,
0x10 = 7 bit,
0x11 = 8 bit.

If bit 2 is set, two stop bits are used. Else only one stop bit.

Bits 3-4 are used to select parity.
0b00 = no parity,
0b01 = odd parity,
0x11 = even parity.
If bit 5 is set, stuck parity is used.

If bit 6 is set, break control is used.

OPENING DEVICES

Device nodes of every device driver reside in the DEV:\ pseudofilesystem.
If the device driver supports it, the device node can be opened to a file
descriptor. If the driver has only one device node and the name of the driver
is foo, the file name is "DEV:\foo". If the driver has multiple devices,
the device number is appended to the name in uppercase hexadecimal notation.
One driver can have 0xFFFF device nodes.

  CLOSE (AX == 3)
  
BX = file descriptor

NULL is returned in AX if success. Else -1 is returned.

Equivalent to C function call fclose(BX);

  LSEEK (AX == 8)
  
DX = file descriptor
CX = mode (0 = SEEK_SET, 1 = SEEK_CUR, 2 = SEEK_END)
BX = count (signed!)

New position is returned in AX.

Equivalent to C function call fseek(DX, BX, CX);

  LLSEEK (AX == 0x8008)

DX = file descriptor
CX = mode
EX:BX = count (signed long)

New position is returned in BX:AX.


  MMAP (AX == 9)
  
BX = data segment to allocate
CX = Length of data segment
DX = File descriptor (optional)
FX:EX = File position added to the current position (optional)

Allocates a new [CX] bytes long memory segment. Tries to allocate segment [BX],
and if fails, tries to allocate other segment. The newly allocated segment is
returned into AX. If [DX] is not 0, contents from file starting from file pos
[FX:EX] are read into the new segment. -1 (0xFFFF) is returned on error.


  MUNMAP (AX == 11)
  
BX = data segment to unallocate

Unallocates (frees) a memory segment that is previously dynamically allocated
with MMAP call. Returns 0 on success and -1 (0xFFFF) on error.


  EXIT (AX == 12)
  
BX = return value

Exits the program and returns. Equivalent to C function call exit(BX);


  GETARGC (AX == 13)
  
Returns program argument count to AX.


  GETARGV (AX == 14)
  
BX = Argument string
CX = Argument string offset

Returns a single character of argument string to AX. Equivalent to C array
read argv[BX][CX].


  SPAWN (AX == 15)
  
BX = Pointer to a buffer where the new program's PID is returned
CX = Pointer to a string containing path to the program executable
DX = Pointer to a string containing program arguments
EX = Privileges

Executes another program. Returns 0 to AX if success, -1 if error.


  Clone (AX == 16)
  
BX = segment of the function that the clone executes
CX = offset address of the function that the clone executes
DX = an interrupt (terminating signal) that is triggered in the parent process
     when the clone exits
EX = pointer to a buffer where the clone's return value is returned
FX = argument to the clone

Makes a new thread. Returns the PID of the new thread into AX. Returns -1 on
error. The clone thread shares the memory space of its parent process. Only
a new stack is allocated for the clone. Argument goes to the clone's AX
register.


  Fork (AX == 17)
  
DX = terminating signal
EX = pointer to the buffer where the clone's return value is returned

Makes a complete copy of the current process. Returns the PID of the clone to
the AX register of the parent, and 0 to the AX of the clone.


  Gettime (AX == 18)
  
Returns 64-bit unsigned presentation of UNIX time to registers AX - DX and
32-bit unsigned presentation of nanoseconds to registers EX - FX.


  Sound (AX == 19)
  
BX = frequency in Hz

Plays sound from PC speaker.


  No sound (AX == 20)
  
Stops playing sound.


  Wait screen retrace (AX == 21)
  
Waits for VGA's vertical retrace.


  Sleep (AX == 22)
  
BX - EX = 64-bit presentation of time when to wake up

Pauses the process and does nothing until wakeup time has passed. The process
can be invoked before that by other processes using the signal SIGCONT.


  Send signal (AX == 23)
  
BX = PID
CX = signal

Sends a signal to the process of that pid. If BX is zero, the signal is sent 
to the caller process itself.


  Process info (AX == 24)
  
BX = process table index
CX = pointer to str buff

If a process is found with the specified index, the pid of the process is
returned into AX register and the process's name is returned to the str buffer.
Returns -1 if no process is found.


  Get priority (AX == 25)
  
BX = process id (own if zero)

Returns process's priority to AX.


  Set priority (AX == 26)
  
BX = process id (own if zero)
CX = new priority

Sets process's priority to CX.


  Fsync (AX == 27)
  
BX = file descriptor

Flushes file output buffer. Returns 0 if success, -1 if error.


  Chdir (AX == 4)
  
BX = pointer to a string containing directory path

Sets the current working directory. Returns 0 if success, -1 if error.


  Opendir (AX == 5)
  
BX = pointer to a string containing directory path

Opens a directory for making a file list. Returns directory descriptor in AX.
Returns -1 if an error happened.


  Readdir (AX == 6)
  
BX = directory descriptor
CX = pointer to a buffer for filename

Reads one filename entry from the directory. Filename is written in the buffer
where CX points to. File attributes are returned in DX register. 0 is returned
to AX, or -1 on error.


  Closedir (AX == 7)
  
BX = directory descriptor

Closes the directory.


  Stat (AX == 10)
  
BX = pointer to return struct
CX = pointer to a string containing filename


Returns information about the file. If no file was found, -1 is returned to AX.
Otherwise 0 is returned and file information is written into the struct pointed
in BX. The struct values are stored like described below:


Offset 0: File attributes (8-bit unsigned)
Offset 1: File size (32-bit unsigned)
Offset 5: Modification timestamp (64-bit unsigned, seconds from Unix epoch)


  Exec (AX == 30)
  
BX = pointer to a string containing path of executable
CX = pointer to a string containing arguments

Runs a program that replaces the current process in memory.
Returns -1 if fails. Normally should not return.


  Dup (AX == 31)
  
BX = old file descriptor

Returns a duplicate file descriptor.


  Dup2 (AX == 32)
  
BX = old file descriptor
CX = new file descriptor

Makes a duplicate file descriptor to file descriptor CX. If there is already
an opened file with the new file descriptor, it is closed.


  Pipe (AX == 33)
  
Makes a pipe. Returns the pipe's read end to BX and the write end to CX.


  Mkdir (AX == 34)
  
BX = pointer to a string containing directory name

Creates a new directory.


  Sendfd (AX == 35)
  
BX = pid of the receiver process
CX = file descriptor

Send a duplicate of the file descriptor to another process. Returns 0 if
the call succeeded, and -1 if the file descriptor could not be sent.

The receiving process gets signal SIGFDRECVD (signal 132).
The duplicate of the file descriptor is returned to the receiving process's
port 0.


  Sethwint (AX == 36)
  
BX = physical interrupt
CX = signal
DX = chain interrupt with old interrupt (0 = false)

Sends a signal to the process every time when an interrupt in BX is triggered
in the computer. The process also instantly gets CPU time.


  Unsethwint (AX == 37)
  
BX = hardware interrupt

Unsets the interrupt signal redirection.


  Loadmod (AX == 28)

BX = pointer to a string that contains path to the TSR program
CX = pointer to a string that contains the name of the device nodes

Loads a module.


  Cmdmod (AX == 29)

BX = pointer to a string that contains name of the device node without the
     preceding "DEV:\"
CX = pointer to the command


  Geterrno (AX == 38)

Returns the last error code to AX.


  Seterrno (AX == 39)

BX = new value of error code

Sets the error code. Used mainly for zeroing the errno.


  Unlink (AX == 40)

BX = path of the file to remove

Removes a file.


  Rmdir (AX == 41)

BX = path of the directory

Removes a directory.


  Setprivs (AX == 42)

BX = PID
CX = privileges

Sets the privileges of process PID. See PRIVS.TXT.


  Getkernelparm (AX == 43)

BX = kernel parameter

Returns the value of the kernel parameter to AX. See KRNLPARM.C for the parameters.


  Setkernelparm (AX == 44)

BX = kernel parameter
CX = new value

Sets the value of the kernel parameter.


  Getcwd (AX == 45)

BX = pointer to destination buffer
CX = maximum number of bytes to copy

Copies the current working directory to the buffer.


  Powersave (AX == 46)

Ends the CPU time of this process and tells the kernel
that this process does not have anything important
to do.


  Unload module (AX == 47)

BX = pointer to string containing module name

Unloads a module.


  Get environment variable (AX == 48)

BX = ID of the variable
CX = maximum length of the string to be stored to the buffer
DX = pointer to destination buffer

Copies an environment variable to the destination buffer. The stored string
is in the form of "NAME=VALUE", where NAME is the name of the environment
variable and VALUE is its value. The string ends in a null character.


  Set environment variable (AX == 49)

BX = pointer to a null-terminated string containing the name of the variable
CX = pointer to a null-terminated string containing the new value of the
     variable
DX = overwrite (0 = no, 1 = yes, 2 = delete variable)

Sets or unsets (if DX == 2) an environment variable.
