Re: [9fans] shared memory

[Ronald G Minnich <rminnich@lanl.gov>]

On Mon, 29 Jul 2002 paurea@gsyc.escet.urjc.es wrote:

> I am writing (or trying to :-)) the driver for the sis630 vga card. It
> uses shared memory, i.e. the video memory comes from the normal ram of
> the computer. At first it seemed to me I had to reserve memory for it
> like a dma buffer, but after looking more closely to the linux driver,
> it seems to me that something hardware is going on and that the memory
> is reserved some way by the bios works as normal video memory. Does
> anybody know how this should be treated?. Any pointers to info?.


sis 630 vga card? don't you mean a motherboard with an sis630 chipset?

Anyway, the sis630 integrated vga uses part of main memory for graphics
memory, called SMA (Shared Memory something). You have to see if it is
enabled (always true with normal bios)  and then see how big it is. Also
the SMA can be supplied by any of the DIMM slots.

Here is the linuxbios code for this.

/* find the device */
        if ((pcidev = pci_find_device(PCI_VENDOR_ID_SI,
PCI_DEVICE_ID_SI_630, NULL)) == NULL)
                return 0;

/* see which banks are enabledd */
        pci_read_config_byte(pcidev, SIS630_BANKENABLE, &dram_status);
        dimm_status = dram_status & 0x7;

/* see if shared memory with integrated vga is enabled */
        sma_enable = dram_status & 0x80;

/* see which dimm is being used for the shared memory */
        pci_read_config_byte(pcidev, SIS630_DIMM_LOCATION_FOR_SMA,
&sma_location);
        sma_location &= 0x03;


        /* compute Shared Menory Area (SMA) size in Mega Bytes */
        sma_size_bits = (dram_status >> 4) & 0x7;
        if (sma_size_bits > 5)
                // this is invalid!
                sma_size = 0;
        else {
                sma_size = (2 << sma_size_bits);
        }


at the end of this code fragment sma (an int) has the shared memory sized
in MB.

let me know if you get this going, we're interested here -- I have a fair
number of these motherboards.

ron