Conference hydra::axp-developer

3265.0. "Paston Chase - Point 21519" by KZIN::ASAP () Tue Mar 04 1997 05:30

    Company Name :  Paston Chase - Point 21519
    Contact Name :  Graham Mann
    Phone        :  44 1603502	061
    Fax          :  44 1603502072
    Email        :  [email protected]
    Date/Time in :   4-MAR-1997 10:30:14
    Entered by   :  Nick Hudson
    SPE center   :  REO

    Category     :  vms
    OS Version   :  6.2
    System H/W   :  


    Brief Description of Problem:
    -----------------------------

From:	ESSB::ESSB::MRGATE::"ILO::ESSC::dlennon"  4-MAR-1997 09:56:32.71
To:	RDGENG::ASAP
CC:	
Subj:	POINT No. 21519, Paston Chase

From:	NAME: ESCTECH@ILO          
	TEL: (822-)6704          
	ADDR: ILO                  <dlennon@ESSC@ILO>
To:	ASAP@RDGENG@MRGATE

Hello - 

POINT Log Number	 21519

Company Name 	Paston Chase 

Engineers name	Graham Mann

Telephone Number 		44 1603502	061

Fax Number		44 1603502072

E-mail Address		[email protected]

Operating System, Version	OpenVMS, V6.2

Platform			Alpha

Problem Statement		

                               INTEROFFICE MEMORANDUM
  
                                          Date: 03-Mar-1997 06:11pm
                                          From:
[email protected]@PMDF@INTERNET
                                          Dept: 
                                          Tel No:   
  
  Subject:  System Time
  
  
Hi,

ASAP No: A60265

Alpha AXP, OpenVMS 6.2, and the 'C' compiler.

I'm trying to port a piece of Macro 32 code:

read_systime current_time		; Get current system time


Which I've duplicated as:

extern unsigned int EXE$GQ_SYSTIME;

union {
    unsigned int qt[2];
    uint64 t_64;
} _align(QUADWORD) current_time;

main()
{
unsigned int *qp;

    qp = &EXE$GQ_SYSTIME;
    current_time.qt[0] = *qp, current_time.qt[1] = *(qp+1);
    printf("Time:[%08X,%08X]\n",
	count,current_time.qt[0],current_time.qt[1]);

    current_time.t_64 = __PAL_LDQP(qp);
    printf("Time:[%08X,%08X]\n",
	count,current_time.qt[0],current_time.qt[1]);
}

The first part works fine.  The idea of the second part was to get the time as
one 
indivisible entity to avoid problems when the least significant integer wraps
back to 
zero.

The __PAL_LDQP poduces the following when executed.
Time:[6322662C,009B0B73]
%SYSTEM-F-OPCDEC, opcode reserved to Digital fault at PC=00030180, PS=0000001B
%TRACE-F-TRACEBACK, symbolic stack dump follows
 Image Name   Module Name     Routine Name    Line Number  rel PC      abs PC
 PCB_VALUE    PCB_VALUE       main                   2682 00000180    00030180
 PCB_VALUE    PCB_VALUE       __main                    0 00000090    00030090
                                                        0 8226C170    8226C170

Is there a better way to get the system time?
Do the __PAL builtins have to be run from kernel mode?


Regards
Graham Mann
Paston Chase
Please e-mail to [email protected]

From:	DEC:.REO.REOVTX::HUDSON       "[email protected] - UK Software
Partner Engineering 830-4121"  4-MAR-1997 11:40:34.82
To:	nm%vbormc::"[email protected]"
CC:	HUDSON
Subj:	RE:POINT No. 21519, Paston Chase, get system time

Hello Graham Mann

The reason you're getting OPCDEC is the LDQP PALcode routine has to be called
from kernel mode.

But I don't think it's what you want anyway, as LDQP is LoaD Quadword at
Physical Address (i.e. reads physical rather than virtual memory).

What you need in your program is to get a LDQ instruction, and you can force
that as shown in the following code.

Since LDQ is atomic, you shouldn't need to take out a lock before reading the
clock.  So this program can be run by a non-privileged user.

Regards

Nick Hudson
Digital Software Partner Engineering

================================================================================
#include <builtins.h>
#include <starlet.h>
#include <limits.h>
#include <ints.h>
#include <stdio.h>

extern unsigned int EXE$GQ_SYSTIME;


union {
	unsigned int qt[2];
	uint64 t_64;
} _align(QUADWORD) current_time;

main()
{
	// because of using "*(qi+1)", we tell the compiler that qi is
	// a pointer to 32bit values
	unsigned int *qi;

	// to force "LDQ", we tell compiler that qp is a pointer to
	// 64 bit values
	uint64 *qp;

	qp = (uint64 *)&EXE$GQ_SYSTIME;
	qi = &EXE$GQ_SYSTIME;

	current_time.qt[0] = *qi, current_time.qt[1] = *(qi+1);
	printf("Time:[%08X,%08X]\n",
		current_time.qt[1],current_time.qt[0]);


	current_time.t_64 = (uint64 )*qp;
	printf("Time:[%08X,%08X]\n",
		current_time.qt[1],current_time.qt[0]);

}