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From: PILLAY.KDA@EXETER.AC.UK
Newsgroups: comp.os.minix
Subject: Calloc, malloc and physical addresses on the PC
Message-ID: <PILLAY.KDA.WTIT@UK.AC.EXETER>
Date: 6 Feb 90 21:12:28 GMT
Sender: Minix operating system <MINIX-L@NDSUVM1>
Reply-To: INFO-MINIX@UDEL.EDU
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Via:        UK.AC.EX;  6 FEB 90 22:12:31 GMT

How!
Can anyone tell me how to obtain the physical 20-bit address for data
allocated using "calloc" or "malloc"?
Under TurboC I have the following:
        unsigned char *ptr
        ..
        ptr = (char *) calloc(num, sizeof(ptr))
        off = ((unsigned) (ptr))
        seg = ((unsigned) ((unsigned long) (ptr) >> 16))

gives me a physical address " seg:off ".

Under MINIX, ptr would only be 2 bytes long. I looked at the floppy.c
driver and that uses "umap(...)" from kernel/system.c which in turn
needs to extract info from a user process etc..
I am programming the DMA controller on the PC and all I want to do
is allocated some memory, using calloc, and program the controller
with the Physical 20 bit address of where ptr points.
Thanks.