reactos操作系统实现(142)
VidInitialize函数主要进行VGA简单视频显示模式初始化。具体实现代码如下：
#001 BOOLEAN
#002 NTAPI
#003 VidInitialize(IN BOOLEAN SetMode)
#004 {
#005 ULONG Context = 0;
#006 PHYSICAL_ADDRESS TranslatedAddress;
#007 PHYSICAL_ADDRESS NullAddress = {{0, 0}};
#008 ULONG AddressSpace = 1;
#009 BOOLEAN Result;
#010 ULONG_PTR Base;
#011
#012 /* Make sure that we have a bus translation function */
确保已经初始化地址总线转换回调函数。
#013 if (!HalFindBusAddressTranslation) return FALSE;
#014
#015 /* Get the VGA Register address */
获取VGA的寄存器地址。
#016 Result = HalFindBusAddressTranslation(NullAddress,
#017 &AddressSpace,
#018 &TranslatedAddress,
#019 &Context,
#020 TRUE);
#021 if (!Result) return FALSE;
#022
检查是否需要映射I/O地址空间。
#023 /* See if this is I/O Space, which we need to map */
#024 TryAgain:
#025 if (!AddressSpace)
#026 {
#027 /* Map it */
#028 Base = (ULONG_PTR)MmMapIoSpace(TranslatedAddress, 0x400, MmNonCached);
#029 }
#030 else
#031 {
#032 /* The base is the translated address, no need to map I/O space */
#033 Base = TranslatedAddress.LowPart;
#034 }
#035
#036 /* Set the VGA Register base and now check if we have a VGA device */
保存VGA的寄存器地址。
#037 VgaRegisterBase = Base;
调用函数VgaIsPresent来判断VGA显示卡是否安装。
#038 if (VgaIsPresent())
#039 {
转换VGA显示内存地址。
#040 /* Translate the VGA Memory Address */
#041 NullAddress.LowPart = 0xA0000;
#042 AddressSpace = 0;
#043 Result = HalFindBusAddressTranslation(NullAddress,
#044 &AddressSpace,
#045 &TranslatedAddress,
#046 &Context,
#047 FALSE);
#048 if (Result)
#049 {
#050 /* Success! See if this is I/O Space, which we need to map */
如果是I/O地址空间，就进行映射转换。
#051 if (!AddressSpace)
#052 {
#053 /* Map it */
#054 Base = (ULONG_PTR)MmMapIoSpace(TranslatedAddress,
#055 0x20000,
#056 MmNonCached);
#057 }
#058 else
#059 {
#060 /* The base is the translated address, no need to map I/O space */
#061 Base = TranslatedAddress.LowPart;
#062 }
#063
设置VGA的内存基地址。
#064 /* Set the VGA Memory Base */
#065 VgaBase = Base;
#066
是否需要显示图片模式。
#067 /* Now check if we have to set the mode */
#068 if (SetMode)
#069 {
复位显示。
#070 /* Reset the display */
#071 HalResetDisplay();
#072 curr_x = 0;
#073 curr_y = 0;
#074
#075 /* Initialize it */
初始化VGA显示。
#076 VgaInterpretCmdStream(AT_Initialization);
#077 return TRUE;
#078 }
#079 }
#080 }
#081 else
#082 {
#083 /* It's not, so unmap the I/O space if we mapped it */
#084 if (!AddressSpace) MmUnmapIoSpace((PVOID)VgaRegisterBase, 0x400);
#085 }
#086
如果初始化失败，重新开始初始化。
#087 /* If we got here, then we failed...let's try again */
#088 Result = HalFindBusAddressTranslation(NullAddress,
#089 &AddressSpace,
#090 &TranslatedAddress,
#091 &Context,
#092 TRUE);
#093 if (Result) goto TryAgain;
#094
运行到这里就表示初始化VGA显示卡失败。
#095 /* If we got here, then we failed even past our re-try... */
#096 return FALSE;
#097 }