tom.storey
Experienced Member
Hi all,
Slightly obscure question, but how does DOS detect the presence of a real-time clock in the system?
I read in a document of DOS interrupt calls that from DOS 3.3 onwards, the calls that it implements that set the date and time will also update the RTC if it is present.
I spent some time today in debug trying to disassemble my way to an answer (under DOS 5.0), and I got some of the way, but then ended up in some really obscure code that I was finding quite difficult to navigate (I havent come close to being an x86 assembly guru yet).
So I thought I might ask and see if someone knows the answer - are there some variables or memory locations that it looks at that describe whether an RTC is present and where it is, or does it use some other "tricks" or methods? Is it as simple as DOS 3.3+ calling the BIOS set date/time functions which on a system with an RTC would then update said RTC? But, while I certainly seemed to be looking at code that was doing very date/time looking things, I never came across any references to int 1Ah though...
Any insight appreciated.
Thanks!
Slightly obscure question, but how does DOS detect the presence of a real-time clock in the system?
I read in a document of DOS interrupt calls that from DOS 3.3 onwards, the calls that it implements that set the date and time will also update the RTC if it is present.
I spent some time today in debug trying to disassemble my way to an answer (under DOS 5.0), and I got some of the way, but then ended up in some really obscure code that I was finding quite difficult to navigate (I havent come close to being an x86 assembly guru yet).
So I thought I might ask and see if someone knows the answer - are there some variables or memory locations that it looks at that describe whether an RTC is present and where it is, or does it use some other "tricks" or methods? Is it as simple as DOS 3.3+ calling the BIOS set date/time functions which on a system with an RTC would then update said RTC? But, while I certainly seemed to be looking at code that was doing very date/time looking things, I never came across any references to int 1Ah though...
Any insight appreciated.
Thanks!