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Old 07 September 2014, 08:29   #38
Ratte
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Join Date: Sep 2008
Location: Germany
Posts: 314
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Regarding unaccessible pci-roms on grex-pci-bridges.

I found out that there might be some kind of mmu-protection around pci-devices used in a grex-board.
Is not easy to get in touch with a rom from a installed pci-device (graphiccards).

Following the pci-specs its easy to point the xrombar to somewhere in the (unused) memorymap and perform a read on it (to build a shadowrom).
After reading the rom, the xrombar must be disabled and the normal bar must be reactivated for normal memoryaccess (graphicsmem).
The grex-problem .... its possible to act normal with the xrombar and bar registers, but the rom is INVISIBLE.

Now pci-specs told us, that you can read a rom or access the memory, but not both at the same time.
So i decided to check what will happen, if i set the xrombar to the memarea where the (deactivated) bar is pointing to ... and voilą ... finally the pci-rom is visible!
Pointing with xrombar to the same area like the deactivated bar (graphicsmem).

Next steps are daily business ... copying the rom to somewhere in the ram .. disable xrombar, activated (mem)bar and so on ...

I just send a message to Radoslaw (strim?) for the netbsd-grex-port.
Maybe on day, the os4-team is able to handle a grex-pci-bridge.
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