Path: utzoo!attcan!uunet!steinmetz!control!dixon
From: dixon@control.steinmetz (walt dixon)
Newsgroups: comp.sys.ibm.pc
Subject: Re: How to respond to a hardware interrupt??
Message-ID: <11652@steinmetz.ge.com>
Date: 26 Jul 88 13:43:16 GMT
References: <130@kolvi.hut.fi> <431@c10sd1.StPaul.NCR.COM>
Sender: news@steinmetz.ge.com
Reply-To: dixon@control.steinmetz.ge.com (walt dixon)
Organization: General Electric CRD, Schenectady, NY
Lines: 46

It is possible and frequently very convenient to write drivers
and TSRs in high level languages like C.  One usually must
write some assembly language glue code to make everything
work;  the amount of assembly language required varies from
compiler to compiler.

Many of the current compilers support an interrupt key
word on a formal procedure definition.  Interrupt
procedures save all registers,  hopefully initialize
the stack and data segments properly,  and exit with
an iret.  Lacking this support,  you will need to write
a short assembly language interface.

Other frequently used assembly language instructions
often are supported through library calls.  Most decent
C /Pascal libraries have outb, inb routines.  If these
routines aren't available,  one can easily write them.
The same is true for enabling/disabling interrupts.
(Some compilers also support imbedded assembly langauge
code.)

There are some issues with the run time libraries.  There
are cases where the call overhead is not acceptable or
the library structure has undesireable side effects
(eg defining a transfer address,  setting up a stack,  etc).
One must approach these libraries with some caution.

The other problem with high level languages is that
you must beat on the linker to get the correct format
for your executable image.  Generally,  it is not hard
to coerce the linker into generating the correct format
image.

There's a place for both C and assembly language.  Certainly
well written C code easier to read than assembly language.
When you design your application,  you have to make some
trade-offs.  I have written TSRs and drivers in both assembly
langauge and C.  All of this code works.

Walt Dixon		{ARPA:		Dixon@GE-CRD.ARPA	}
			{US Mail:	GE CRD			}
			{		PO Box 8		}
			{		Schenectady,  NY 12345	}
			{Phone:		518-387-5798		}

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