I have a PC/104 bus based NVRAM card. It’s just a battery backed NVRAM chip and an address decoder chip so it has absolutely no intelligence at all.
The sum total of documentation is some circuit/mechanical diagrams and a comment that this memory is mapped to A0000.
I have attempted to map this memory using
mmap_device_memory(NULL,0x8000 ,PROT_NOCACHE | PROT_READ | PROT_WRITE,0,0xA0000); // 8000 as it’s the smallest cheapest size at 32k
and it seems to retain the data written to it until I reboot the hardware.
Mind you it does the same if I unplug the NVRAM card.
From which I conclude that it is not accessing NVRAM at all but the RAM on the cpu card.
Should the mmap_device_memory card map the specified area as outside the CPU RAM or is there further setup I must do before attempting to the access the card or assuming the card is a duff ?
The call looks ok to me, but isn’t A0000 used by VGA memory?
Yup.
VGA Frame buffer it seems.
Even defined as such in the manual of a fairly recent PC/104 card.
The more expensive NVRAM card with megabytes on allows base address selection that includes c8000,D0000,D8000 which being the ISA memory areas would make more sense.
I wait a response from the US goons with low expectations having queried the wisdom of mapping so low.
I hope for your sake they aren’t using plug and play