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IN and OUT

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i've been playing around with some driver development for windows. I've noticed a few issues with IN and OUT. Currently just for my own amusement i'm working on serial port driver that communicates with the UART chip on port 0x3F8 (com 1). I've noticed that when I run my driver anything i read from the registers returns 0xFF unless something in windows has an open handle to a serial port in which case it returns the proper value of what i wrote to it. Also I've noticed that i can't set PIC masks on port 0x21, i can only ever read back 0 from there ( all interrupts enabled ). I've done some interfacing with an APIC before and I've had no issues working with interrupt masks. Is there an ability to disable access to certain ports that I'm unaware of? I'm just looking for an explanation.

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