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FAQ.md

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What is the benefit?

Depending on the circumstances VirtualSMC can bring better compatibility with present and future macOS releases providing broader SMC feature support and allowing more flexible SMC key emulation like MMIO, events (like in SMCLightSensor), permission support, etc. On older Macs it can be used to upgrade SMC generation with more features.

What are the requirements?

macOS 10.4 or newer. Compatible Lilu is required for full functionality, basic functionality will be available even on beta macOS versions or with -liluoff boot-arg. Bootloader support is recommended for boot.efi compatibility when FileVault 2 is enabled. Legacy VirtualSMC.efi module can be used for incompatible bootloaders. SMCHelper-64.efi is not compatible with VirtualSMC.efi and must be removed.

How can I debug issues?

Using DEBUG kexts and the usual boot-args to enable debug information in relevant kexts. Other than -vsmcdbg and generic boot-args like keepsyms=1, -v, debug=0x100, io=0xff you may be interested in AppleSMC debug support (smc=0xff) or AppleSmartBatteryManager debug support (batman=0xff). On 10.13 or newer you may have to patch the kernel to be able to view the panic trace without the subsequent kext list. Good luck.

Why does VirtualSMC show in every page fault kernel panic?

In most cases VirtualSMC is unrelated to any kernel panic you experience. The reason it is present in stacktrace is becauase VirtualSMC wraps kernel_trap to emulate SMC device.

What is special about sensors?

Sensor kexts provide extra monitoring functionality like temperature, voltage, or extra functionality in dedicated SMC keys. The list of known SMC keys and sensors could be found in Docs directory. You are welcome to implement your own sensor kexts using a dedicated API, but check the basic manual first.

Why does sensor X not show the information in Y?

Make sure, that the information you are looking for is actually implemented in sensor X by checking the SMC key values (run smcread -s). If it is not, then make sure that this information is present on Apple hardware and consider making a pull-request. If it is not, then make sure that the software you check the information with does try to read the relevant key. Be aware, that some software like iStat Menus implement special sensor profiles based on Mac platform, and may not read all the sensors available.

Is authenticated restart supported?

Authenticated restart, normally invoked by sudo fdesetup authrestart, see man fdesetup, is supported when bootloader support or VirtualSMC.efi are present. However, it is insecure just as any software implementation is. If you care about privacy and security, you should disable it by passing vsmchbkp=0 boot-arg.

The VirtualSMC implementation stores the encryption key in nvram and may encrypt it with a temporary key if higher RTC memory bank is available. Other than that, AptioMemoryFix will try to prevent reads of the encryption key after EXIT_BOOT_SERVICES, if installed.

What are the files in Docs?

  • SMCBasics.txt contains generic information about SMC
  • SMCKeys.txt contains some upated SMC key descriptions (complements html docs)
  • SMCKeysMacPro.html contains SMC key descriptions for old MacPro
  • SMCSensorKeys.txt contains libSMC.dylib SMC sensor key descriptions
  • SMCDumps contains SMC key dumps created by running smcread -s, please add more!
  • SMCDatabase contains SMC firmware dumps created with smcread from Apple updates
  • SMCTypes contains summarised SMC key lists across SMC generations based on SMCDatabase
  • iStat.txt contains iStat Menus key profiles (FauxMac is a profile when FakeSMC service is detected)
  • MacModels.txt contains board-id <--> mac-model summary with SMC firmware dump statuses
  • SensorInfo.md contains basic sensor how-to

What are the tools all about?

  • rtcread allows to access RTC/CMOS memory and contains relevant AppleRTC information
  • smcread allows to access SMC keys, dump SMC firmwares and libSMC.dylib
  • smc-fuzzer is a fork of an old smc tool with some features missing in smcread
  • libaistat allows to dump SMC key profiles from iStat Menus when used with DYLD_INSERT_LIBRARIES

What are the sensors for?

  • SMCLightSensor implements an example of illumination sensor handling with a new SMC event API (requires ACPI0008/_ALI)
  • SMCBatteryManager implements a complete emulation layer of AppleSmartBattery of SMC and SMBus protocols
  • SMCProcessor implements temperature monitoring for Penryn CPUs or newer
  • SMCSuperIO implements support fans reading