VGA_ATC_OVERSCAN
vga_wattr(cinfo->regbase, VGA_ATC_OVERSCAN, 0x00);
svga_wattr(regbase, VGA_ATC_OVERSCAN, 0x00);
par->atc[VGA_ATC_OVERSCAN] = 0x00; /* 0 for EGA, 0xFF for VGA */
par->atc[VGA_ATC_OVERSCAN] = 0;
atc[VGA_ATC_OVERSCAN] = 0x00; /* 0 for EGA, 0xFF for VGA */