CR31
i810_writeb(CR_INDEX_CGA, mmio, CR31);
unsigned char CR31, CR32, CR33, CR34, CR36, CR3A, CR3B, CR3C;
reg->CR31 = 0x8c;
vga_out8(0x3d5, reg->CR31, par);
reg->CR31 = vga_in8(0x3d5, par);
vga_out8(0x3d5, reg->CR31, par);