PSIONICS FILE - PROCESS
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Processes and their properties
Last modified 1997-09-11
==============================
The Series 3 operating system is a fully multitasking one; at any time it can
be running any number of processes (up to some limit). Much useful information
about processes can be displayed with the SPY program.
Each process has a name, a task number, and a process ID. The task number runs
from 1 upwards (the Series 3 is limited to 24), and a task number can be
reused whenever a process terminates. The process ID consists of the address
of the control block for the process in kernel memory in the bottom 12 bits,
and a simple counter in the top 4 bits; this starts at 0 for the first
process to use this control block, and is incremented whenever the block is
reused.
The name of a process is normally the name of the program (1 to 8 characters),
followed by ".$" (or ".@" for subtasks), and the task number as 2 decimal
digits. The code for a process is placed in a segment called by the name of
the program followed by ".SC". Thus it is not possible to run two programs
with the same name at the same time.
Each process has a priority. Non-operating system processes are limited to
priority 192; the normal priorities are 128 for foreground and 112 for
background. Only the highest priority process(es) able to run will do so; all
lower priority ones will wait.
System processes
----------------
There are two kinds of system processes: fixed ones and optional ones. The
fixed processes are:
SYS$NULL.$01 handles power off
SYS$MANG.$02 the process and resource manager
SYS$FSRV.$03 the file server
SYS$WSRC.$04 the window server
SYS$SHLL.$05 the process launcher and system screen
TIME.$06 the time and alarm server
The optional processes are:
SYS$NCP.$?? the remote link manager
Registers
---------
Processes may use the data registers (AX, BX, CX, DX, SI, and DI) without
restriction. The kernel may move memory segments about in memory at any time
without warning; when it does so, those of the segment registers (CS, DS, ES,
and SS) that appear to the kernel to be valid will be adjusted automatically.
If it is desired to change these registers at any other time, it should
therefore be done with interrupts disabled.
OPL uses CS, DS, and SS, and these should not be altered by assembler code
invoked from with OPL. ES is not used by the OPL interpreter, and is normally
left the same as DS and SS (which are always the same). Many system calls
use data registers to hold pointers; a segment register is also used with
each such pointer. The Psionics files SYSCALLS.n indicate when an address is
using ES; they do not distinguish DS and SS. Any assembler code called from
OPL should exit with ES equal to DS.
The only other values that can usefully be placed in ES are the kernel data
segment (using system call GenDataSegment), and segments created with the
system call SegCreate. To do the former, just invoke INT $8F; ES will then
point to the kernel data segment, and accesses via ES will behave just as
if done with the system call GenGetOsData (it is not possible to write in
this way). The latter is done as follows:
; Assume the segment handle is in BX.
INT $8F
MOV ES,ES:[BX]
; ES now points to the start of the segment.
; If the segment moves, ES will change automatically.
; Before returning to OPL:
CLI ; with interrupts disabled
PUSH DS ; copy DS to ES
POP ES
STI ; and allow interrupts again
Memory
------
Each process has a single segment of memory. From zero upwards, this contains:
reserved statics
stack (grows downwards)
normal statics
heap (grows upwards)
The heap is divided into allocated and free cells. The SPY program shows the
number and total byte count of each kind of cell. The kernel will remove free
cells from the end of the heap when it needs space.
The stack is initialized to all $FF; it must always hold at least 256 bytes
to allow interrupts to be processed (otherwise panic 69 will occur). A typical
stack size is $A00. The SPY program allows the unused portion of the stack to
be refilled with $FF (to allow the high water mark to be reset).
The heap consists of consecutive cells:
Offset 0 (word): length of data portion (L)
Offset 2 to L+1: data portion (whose address is returned by allocators)
@Is that right, or is it 2 to L-1 ?@
Cells are always aligned to even addresses, and for this and other reasons may
be larger than requested.
Specific memory locations
-------------------------
The following table lists some specific use of memory locations.
Offset 0 (word): initialized to $DEAD; should never change
Offset 2 to 5: used by the kernel
Offset 6 (word): handle of the segment holding the fold tables @@
Offset 8 to 15: used by the object oriented programming system
Offset 16 (word): used by the kernel
Offset 18 (word): address of block
Offset 20 (word): handle of the application manager object
Offset 22 to 25: used by the window server
Offset 26 to 29: used by the OPL runtime system
Offset 30 (word): used by the debugger
Offset 32 (byte): zero when address trapping is turned off (do not alter)
Offset 33 (byte): non-zero when the kernel is modifying the heap
Offset 34 (word): address of cstr holding the program name; used to determine
which list on the system screen a process appears in (@if
this word is zero, the process will not be sent X messages)
Offset 36 (word): address of a heap cell containing a cstr holding the full
path name of the program being executed, followed by a
qstr holding the program information (see system call
FilExecute).
Offset 38 (word): not used by the kernel or OPL; used by the debugger
Offset 40 to 53: not used by the kernel or OPL
Offset 54 (word): address of current dialog structure
Offset 56 (word): @@ DatGate object handle
Offset 58 (word): non-zero if locked (by OPL "LOCK ON" or equivalent)
Offset 60 (word): address of cstr to appear in the status window
Offset 62 (word): address of cstr holding current file being processed
Offset 64 : maximum limit of stack (if floating point emulation is
in use, the emulator uses offsets 64 to 767).
Certain of these memory locations have names in the system documentation:
34 DatProcessNamePtr
36 DatCommandPtr
40 DatApp1
42 DatApp2
44 DatApp3
46 DatApp4
48 DatApp5
50 DatApp6
52 DatApp7
58 DatLocked
60 DatStatusNamePtr
62 DatUsedPathNamePtr
@Location "winHandle" is the channel number of the console device.
Block has the following contents:
@this is a "wserv" object@
Offset 32 (word): address of block
Block has the following contents:
Offset 12 (word): address of block
Block is created by the MINIT keyword and destroyed by the MENU
keyword. Outside this range, the block is invalid, and the pointer in the
block is invalid. Each MCARD keyword can move this block, thus
altering that pointer. The block has the following contents:
Offset 0 (byte): number of MCARD calls so far
Offset 1 onward: menu information blocks, in order of menu creation
Each menu information block has the following contents:
Offset 0 (word): address of secondary menu information block
Offset 2 (cstr): menu title
Each secondary menu information block has the following contents:
Offset 0 (long): [Only ever seen $7392A1DF]
Offset 4 (word): number of items in the menu
Offset 6 (long): [Only ever seen 1 so far]
Offset 10 (word): address of item table
Each item table has the following contents:
Offset 0 (byte): number of items in the menu
Offset 1 onward: item information blocks, in order of item
Each item information block has the following contents:
Offset 0 (byte): number of bytes in the block, excluding this one
Offset 1 (byte): Psion+ accelerator code (lowercased)
Offset 2 (cstr): item text
Time process
------------
The pending alarms can be located in the memory of the Time process. At some
location between offset $0A00 and $0AFF is a block with the form:
Offset 0 (long): $08040201
Offset 4 (long): $00402010
Offset 12 (word): first alarm control block
It is reported that on the Series 3c this has moved to somewhere between
$0C00 and $0CFF. It is also reported that on some versions the control
block is at offset 10 or 15.
The alarm control blocks are in a circular list, with the last pointing to
offset 12 (or 10 or 15) of the above block (which is not an alarm control
block); if that location points to itself, there are no alarms. Each block
has the form:
Offset 0 (word): next alarm control block
Offset 2 (word): reported that this is the second next alarm control block
Offset 6 (word): process ID of process owning alarm
Offset 8 (byte): 0 = clock alarm, 1 = has time and date, 2 = has date
Offset 10 (long): abstime alarm expires
Offset 14 (long): abstime displayed in alarm message
Offset 18 (qstr): name of alarm sound
Offset 28 (cstr): text displayed in alarm message
Offset 93 to 255: [unknown; alleged to be part of the block]
The built-in alarm sounds have names consisting of a single byte (thus
offset 18 is 1 and offset 19 holds the name): 1=rings, 2=chimes, and
16=silence.
@System screen or Window Server (which?) places info about 14 application
buttons at DatApp1.@
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