On 10 Mar 2006, at 10:22, Miguel wrote: > > > M> For example, the timer ticker interrupt at 1Ch (or 08h). > > > > For timer operation DOS uses BIOS. > > One can read the timer tick out of the BIOS Data Area, but in order to get > interrupt notification of timer ticks one must hook int 1Ch (or 08h) > > It seems to me that FreeDOS must hook into the BIOS ticker interrupt in > order to get notification of ticks. Probably 1Ch ... but that is not > happening in this code ... so that makes me wonder whether or not there is > someplace else in the FreeDOS code that is hooking the timer interrupt. No, FreeDOS does not hook the timer interrupt. FreeDOS calls INT10h, ah = 0 to get the tick counter. BIOS is providing the INT08h Interrupt handler, which counts the ticks and stores them in the BIOS Data Area.
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