A1200 DBOX Mediator Fast ata ETC

[tjaoz]

@MskoDestny

To be more specific, the Mediator only allows access to 8MB of PCI memory at a time due to the limitations of the trapdoor expansion slot.

More precisely speaking, it isn't the limitation of the trapdoor expansion slot, but the limitation of the A1200 turbo cards. Existing A1200 turbo cards have only 24 address lines connected to the trapdoor slot, instead of 32 address lines supported by this slot.

The Mediator hardware does provide banked access to the whole 4GB PCI address space (i.e. the driver has to write to a register to change the bank).

You are right here.

The 2D graphics drivers have been written to work around this limitation, but the 3D drivers have not (and never will).

Actually it's quite opposite.

Warp3D drivers have access to the whole Voodoo graphic card resources - it means to the Voodoo registers and to 16MB (or 32MB in case of V4 and V5) of the Voodoo graphic memory. The limitation is that the Picasso96 2D graphic system can use only 8MB of the gfx card memory when Mediator works in the NO-MMU mode. The rest of the Voodoo card memory is then used by the Warp3D textures and the PCI DMA buffers.

[tjaoz]

@MskoDestny

Well there are 8 reserved pins that could theoretically be used for the rest of the address bus, but generally speaking it's unwise to use reserved pins for anything

These trapdoor pins (no. 1 to are not reserved for "anything".  :-D  They are reserved for A24 to A31 address lines (check the schematic of A1200 main board).

So, if the A24 to A31 address lines of the existing turbo cards are not connected to the trapdoor slot, it is certainly a limitation of the turbo cards, not the limitation of the A1200 trapdoor slot.

I don't see how Warp3D can use more than 8MB of texture memory (apart from using the MMU).

You explained it yourself: "The Mediator hardware does provide banked access to the whole 4GB PCI address space (i.e. the driver (Warp3D driver in this case) has to write to a register to change the bank)".  :idea: