IYONIX pc only

• Installing a second graphics card

  The primary graphics card, ie. the one which will be used when Geminus is not running, will be the lowest one when fitted in the tower case. Since IYONIX pcs are supplied with their graphics card in a 64-bit slot, this will likely be your original card.

  We believe there is an issue with the use of multiple recently-supplied (JATON) graphics cards in the Iyonix and another, unrelated issue with the use of older cards (as shipped with pre-production machines) in 32-bit slots. To avoid both of these issues, we recommend that you install the second graphics card in a 32-bit slot (either of the two righthand slots that have shorter, white sockets on the motherboard).

  Also some users may find that it helps to swap over their original graphics card and the USB card/terminator pair if they are installing their new graphics card in the slot closest to the existing cards. This can give slightly better clearance between the cards and eliminates any chance of the USB card's metal pins contacting the new graphics card.

  Lastly, RISC OS 5.09 and 5.10 are modified slightly with the setup of your graphics card(s) when they are programmed into the flash ROM so it is inadvisable to change the card positions after programming. This decision was taken by Castle to resolve startup problems but, since it can prevent the machine from booting with alternative cards/positions, we sincerely hope that are more workable solution will be found.

Acceleration feature

Geminus is able to accelerate the desktop by using the NVIDIA graphics card hardware more extensively than RISC OS 5 does, and by reducing the amount of data that is transferred over the PCI bus bottleneck. This is achieved by remembering sprites and window contents in the off-screen memory of the NVIDIA card being used so that they can be redrawn straight from the card's memory. This is called 'cacheing.'

The NVIDIA card currently being shipped with the IYONIX pc, or available as an extra from Spellings, has 64MB of on-board video RAM yet the screen display can only consume 12MB of that memory even with a high resolution mode such as 2048 x 1536 x 32bpp. This leaves a lot of wasted memory that Geminus can put to good use cacheing frequently-plotted sprites and window contents.

DMA-accelerated sprite plotting

The OS sprite plotting code makes no attempt to accomodate the architecture of the IYONIX pc, which really requires prefetching of sprite data and burst writes to the PCI bus. When developing the video output stage of the Cino DVD player it was discovered the IOP321's DMA channel is capable of performing these transfers much more rapidly than the XScale CPU and Geminus puts this hardware to good use when plotting large sprites of the same bit depth as the screen.

Since most IYONIX pc users will be using 32bpp modes, the effect of DMA-accelerated plotting will be apparent when viewing large JPEGs in !ChangeFSI, large 32bpp sprites in !Paint and all large images in !NetSurf if the image settings are 'Use OS' in NetSurf's Choices window.

Horizontal and vertical lines

Geminus can employ the NVIDIA's hardware acceleration for rendering horizontal and vertical lines (eg. window borders and DrawFile rendering) to give a speed increase over the OS rendering routines. This will give a further boost in a future version of Geminus that can overlap graphics operations with CPU activity.

Inversions

Inverting a rectangular area of the screen is a very slow operation on the IYONIX pc because it requires that a large amount of data be read over the PCI bus from the NVIDIA card, inverted by the CPU and then written back. The very poor performance of this operation is apparent when selecting rows and columns in !Paint, for example.

Geminus can use the NVIDIA hardware to perform this operation literally thousands of times faster, making these selections much slicker and far more pleasant to use.

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