added VGM playback
This commit is contained in:
Ilu
157
src/lib/pctimer/readme.txt
Normal file
157
src/lib/pctimer/readme.txt
Normal file
@@ -0,0 +1,157 @@
|
||||
PCTIMER: Millisecond Resolution Timing Library for DJGPP V2
|
||||
Version 1.4 Release Notes
|
||||
March 15, 1998
|
||||
Status: Freeware.
|
||||
Distribution status: Has to be distributed as this archive.
|
||||
Send comments to: Chih-Hao Tsai (hao520@yahoo.com).
|
||||
|
||||
|
||||
==== A FEW WORDS ON WIN95
|
||||
|
||||
Although I have only tested PCTIMER with Win95 and CWSDPMI,
|
||||
PCTIMER should run on most DPMI servers.
|
||||
|
||||
However, theoretically, applications running under Win95
|
||||
should not touch hardware interrupts. The "correct" method
|
||||
of doing millisecond resolution timing under Win95 is to call
|
||||
Windows API. The standard Multimedia Timer API can do
|
||||
millisecond resolution timing. (You'll need to include
|
||||
<mmsystem.h> and link with winmm.lib. But, as far as I know,
|
||||
RSXNT does not provide Multimedia API access.)
|
||||
|
||||
If you need an example on using Windows API to do millisecond
|
||||
resolution timing, check this out (I used Visual C++ 4.0):
|
||||
|
||||
Test Report: Millisecond Resolution Timing with Win95/VC4
|
||||
http://www.geocities.com/hao510/w98timer/
|
||||
|
||||
|
||||
==== BASIC LOGIC
|
||||
|
||||
PCTIMER reprograms the 8454 IC (Programmable Interrupt Timer)
|
||||
to get high frequency of System Timer Interrupt (IRQ0) whose
|
||||
default frequency is 18.2 Hz. Since the operating systems
|
||||
rely heavily on the System Timer Interrupt, increasing its
|
||||
frequency could cause instability. PCTIMER hooks both
|
||||
protected and real mode int 8h handlers (default handler for
|
||||
System Timer Interrupt) reprograms 8254 to get higher
|
||||
frequency of interrupts, but calls the original handlers at
|
||||
a fixed frequency of 18.2 Hz.
|
||||
|
||||
|
||||
==== RELATIONSHIP BETWEEN PROTECTED & REAL MODE INT 8H
|
||||
|
||||
According to DJGPP V2 FAQ, hardware interrupts are always
|
||||
passed to protected mode first, and only if unhandled are
|
||||
they reflected to real mode. In other words, we must at least
|
||||
hook protected mode int 8h. To avoid potential loss of ticks
|
||||
when the protected mode fails to handle the hardware
|
||||
interrupt, we should also hook real mode int 8h.
|
||||
|
||||
In actual implementation of the two handlers, things become
|
||||
much more complex than that.
|
||||
|
||||
|
||||
==== PCTIMER PROTECTED MODE INT8H HANDLER
|
||||
|
||||
Here is PCTIMER's protected mode int 8h in pseudo code. The
|
||||
meanings of pm_termination_flag's values are:
|
||||
|
||||
TRUE_FAILURE: The handler failed to handle the hardware
|
||||
interrupt.
|
||||
|
||||
CHAIN_TERMINATION: The handler terminated with chaining to
|
||||
the old handler. Note that after chaining the old protected
|
||||
mode int 8h handler, the *real* mode int 8h *will* get called.
|
||||
We need to take care of this.
|
||||
|
||||
OUTPORTB_TERMINATION: The handler terminated with an
|
||||
outportb (0x20, 0x20) instruction. This instruction sends
|
||||
a hardware request to the Interrupt Controller to terminate
|
||||
the interrupt. This works (although intrusive), but will
|
||||
cause the DPMI server to believe that the protected mode
|
||||
handler failed to do its job. Therefore, the real mode
|
||||
handler *will* get called. We need to take care of this,
|
||||
too.
|
||||
|
||||
(Read the real code for details.)
|
||||
|
||||
PCTIMER Protected Mode Int 8h Handler (Pseudo-code)
|
||||
* pm_termination_flag = TRUE_FAILURE
|
||||
* counter++
|
||||
* if it is time to chain old handler
|
||||
- pm_termination_flag = CHAIN_TERMINATION
|
||||
- let the wrapper chains the old handler
|
||||
* else
|
||||
- pm_termination_flag = OUTPORTB_TERMINATION
|
||||
- outportb (0x20, 0x20)
|
||||
|
||||
|
||||
==== PCTIMER REAL MODE INT8H HANDLER
|
||||
|
||||
The real mode handler is considerably more complex than the
|
||||
protected mode one. It depends on pm_termination_flag to
|
||||
determine how it should behave. Always set
|
||||
pm_termination_flag to TRUE_FAILURE before we leave, so in
|
||||
case the protected mode handler should fail, the real mode
|
||||
handler can detect it next time.
|
||||
|
||||
(Read the real code for details.)
|
||||
|
||||
PCTIMER Real Mode Int 8h Handler (Pseudo-code)
|
||||
* if pm_termination_flag = TRUE_FAILURE
|
||||
- counter++
|
||||
* if it is time to chain the old handler, or if the protected
|
||||
mode handler decided to do that (i.e.,
|
||||
pm_termination_flag = CHAIN_TERMINATION)
|
||||
- call old real mode handler
|
||||
- pm_termination_flag = TRUE_FAILURE
|
||||
* else
|
||||
- outportb (0x20, 0x20)
|
||||
- pm_termination_flag = TRUE_FAILURE
|
||||
|
||||
|
||||
==== Example of Usage
|
||||
|
||||
#include <gccint8.h>
|
||||
|
||||
void main (void)
|
||||
{
|
||||
unsigned long int start, finish, elapsed_time;
|
||||
|
||||
/* initiate the timer with 1/1000 s resolution */
|
||||
/* you can use different resolution, but resolution */
|
||||
/* higher than 1000 is not recommended. */
|
||||
|
||||
pctimer_init (1000);
|
||||
|
||||
start = pctimer_get_ticks ();
|
||||
/* do some stuff here */
|
||||
finish = pctimer_get_ticks ();
|
||||
elapsed_time = pctimer_time (start, finish);
|
||||
/* always returns elapsed time in the unit of ms. */
|
||||
|
||||
pctimer_sleep (200); /* sleep 200 ms */
|
||||
pctimer_sound (800, 200); /* 800 Hz sound for 200 ms */
|
||||
|
||||
/* never forget to exit the timer!!! */
|
||||
/* otherwise, the system WILL crash!!! */
|
||||
|
||||
pctimer_exit ();
|
||||
}
|
||||
|
||||
|
||||
==== HISTORY
|
||||
3/15/98 Version 1.4
|
||||
11/26/95 Version 1.3
|
||||
1/29/95 Version 1.2
|
||||
1/16/95 Version 1.1
|
||||
11/5/94 Version 1.0
|
||||
|
||||
|
||||
==== DISCLAIMER
|
||||
|
||||
I am not at all responsible for any damages, consequential
|
||||
or incidental, and by using PCTIMER, you are agreeing not
|
||||
to hold either of the above responsible for any problems
|
||||
whatsoever.
|
||||
Reference in New Issue
Block a user