The Minnowboard Chronicles Episode 8: the Reset Vector, and Boot Flow

This is getting pretty intense. It’s time to explore the code that executes at the reset vector, and see the printf messages coming out of the BIOS as the Minnowboard boots.

Having gotten past my reset issues on the Minnowboard, I set a hard breakpoint directly at the reset vector (which is at physical address FFFFFFF0h on the Minnowboard). The reset vector is the default location (address) where the BayTrail CPU finds the first instruction it will execute after a reset. You can see these first instructions in the SourcePoint debugger Code window:

Breakpoint at reset vector

There are a couple of NOP instructions, followed by a near JMP to address FFFFF6B8. Everything is in assembly language because the initial code is being executed out of flash memory. Looking at the code at FFFFF6B8 is informative.

Reset vector FFFFF6B8

The first instruction there is FPINIT, which initializes the processor floating point unit (FPU). Then there is some more assembly language code, which I will have to determine the meaning of later. It’s a good time to load the PEI modules and try to see some source code somewhere, by clicking on the PEIMs button at the top of the screen. An excerpt of the output within the Command window looks like this:


PlatformEarlyInit              Entry: FFF203A0L Base: FFF20140L  "c:\myworkspace\Build\Vlv2TbltDevicePkg\DEBUG_VS2012x86\IA32\Vlv2TbltDevicePkg\PlatformInitPei\PlatformInitPei\DEBUG\PlatformEarlyInit.efi"

PchSmbusArpDisabled            Entry: FFF29C20L Base: FFF299C0L  FILE NOT FOUND "m:\Build\Vlv2TbltDevicePkg\DEBUG_VS2008x86\IA32\Vlv2DeviceRefCodePkg\ValleyView2Soc\SouthCluster\Smbus\Pei\PchSmbusArpDisabled\DEBUG\PchSmbusArpDisabled.pdb"

VlvInitPeim                    Entry: FFF2B820L Base: FFF2B5C0L  FILE NOT FOUND "m:\Build\Vlv2TbltDevicePkg\DEBUG_VS2008x86\IA32\Vlv2DeviceRefCodePkg\ValleyView2Soc\NorthCluster\VlvInit\Pei\VlvInitPeim\DEBUG\VlvInitPeim.pdb"

PchInitPeim                    Entry: FFF2DA00L Base: FFF2D7A0L  FILE NOT FOUND "m:\Build\Vlv2TbltDevicePkg\DEBUG_VS2008x86\IA32\Vlv2DeviceRefCodePkg\ValleyView2Soc\SouthCluster\PchInit\Pei\PchInitPeim\DEBUG\PchInitPeim.pdb"

PchSpiPeim                     Entry: FFF33280L Base: FFF33020L  FILE NOT FOUND "m:\Build\Vlv2TbltDevicePkg\DEBUG_VS2008x86\IA32\Vlv2DeviceRefCodePkg\ValleyView2Soc\SouthCluster\Spi\Pei\PchSpiPeim\DEBUG\PchSpiPeim.pdb"

PeiSmmAccess                   Entry: FFF35880L Base: FFF35620L  FILE NOT FOUND "m:\Build\Vlv2TbltDevicePkg\DEBUG_VS2008x86\IA32\Vlv2DeviceRefCodePkg\ValleyView2Soc\CPU\SmmAccess\Pei\SmmAccess\DEBUG\PeiSmmAccess.pdb"

PeiSmmControl                  Entry: FFF37000L Base: FFF36DA0L  FILE NOT FOUND "m:\Build\Vlv2TbltDevicePkg\DEBUG_VS2008x86\IA32\Vlv2DeviceRefCodePkg\ValleyView2Soc\SouthCluster\SmmControl\Pei\SmmControl\DEBUG\PeiSmmControl.pdb"

S3Resume2Pei                   Entry: FFF38280L Base: FFF38020L  "c:\myworkspace\Build\Vlv2TbltDevicePkg\DEBUG_VS2012x86\IA32\UefiCpuPkg\Universal\Acpi\S3Resume2Pei\S3Resume2Pei\DEBUG\S3Resume2Pei.efi"

A number of the modules cannot be found. But for those that are, there are handy pointers to the source build tree and where the .MAP files are. More on this later.

As I prepare to delve even further into the source code involved in the early boot process, the other indispensable aid is to take advantage of the debug printf statements that come out of the serial port of the Minnowboard. I obtained an inexpensive serial-to-USB cable on Amazon, and hooked it up to my Mac using the CoolTerm application. That is when things got really exciting: as I booted up the system, I saw some very interesting information come out to the terminal. An excerpt of the first couple of screens are:


Mono Status Code PEIM Loaded

Install PPI: 1F4C6F90-B06B-48D8-A201-BAE5F1CD7D56

Install PPI: AB294A92-EAF5-4CF3-AB2B-2D4BED4DB63D

Register PPI Notify: F894643D-C449-42D1-8EA8-85BDD8C65BDE

DetermineTurbotBoard() Entry

MmioConf0[0xFED0E200], MmioPadval[0xFED0E208]

Gpio_S5_4 value is 0x3

Gpio_S5_17 value is 0x3

GGC: 0x00000210 GMSsize:0x00000002

CheckCfioPnpSettings: CFIO Pnp Settings Disabled

DetermineTurbotBoard() Entry

MmioConf0[0xFED0E200], MmioPadval[0xFED0E208]

Gpio_S5_4 value is 0x3

Gpio_S5_17 value is 0x3


Setup MMIO size …

Install PPI: E767BF7F-4DB6-5B34-1011-4FBE4CA7AFD2


    PDB = m:\Build\Vlv2TbltDevicePkg\DEBUG_VS2008x86\IA32\Vlv2DeviceRefCodePkg\Txe\SeCUma\SeCUmaPeim\DEBUG\SeCUma.pdb

Loading PEIM at 0x000FFFA2E20 EntryPoint=0x000FFFA3080 SeCUma.efi


Install PPI: CBD86677-362F-4C04-9459-A741326E05CF

Info: SeC PPI load sucessfully


    PDB = c:\myworkspace\Build\Vlv2TbltDevicePkg\DEBUG_VS2012x86\IA32\SourceLevelDebugPkg\DebugAgentPei\DebugAgentPei\DEBUG\DebugAgentPei.pdb

Loading PEIM at 0x000FFFA49A0 EntryPoint=0x000FFFA4C00 DebugAgentPei.efi


Install PPI: 3CD652B4-6D33-4DCE-89DB-83DF9766FCCA

Debug Timer: FSB Clock    = 200000000

Debug Timer: Divisor      = 2

Debug Timer: Frequency    = 100000000

Debug Timer: InitialCount = 10000000

Register PPI Notify: F894643D-C449-42D1-8EA8-85BDD8C65BDE

Set MRC paramaters for MinnowBoard Max.

MmioConf0[0xFED0E220], MmioPadval[0xFED0E228]

Gpio_S5_5 value is 0x3

Determine the memory size is [2GB]

DRAM_Speed is 1066MHz!

DRAM_Speed is type 1, EccEnabled = 0

tCL = 7

tRP_tRCD = 7

tWR = 8

tWTR = 5

tRRD = 6

tRTP = 4

tFAW = 28




MRC getting memory size from SeC …

SeC Device ID: F18

SeC UMA Size Requested: 16384 KB

MRC SeCUmaSize memory size from SeC … 10

MRC getting fTPM memory size from SeC …

MRC SeCfTPMUmaSize memory size from SeC … 0





Configuring Memory…

CheckMicrocodeRevision  = 00000906, CpuId = 00030679

####: ConfigureMemory() Entry

Current function  is MMRC_Init

 Current function  is McEnableHPET

 Current function  is ClearSelfRefresh

 Current function  is OemTrackInitComplete

 Current function  is ProgSFRVolSel

 Current function  is ProgDdrTimingControl

 Current function  is ProgBunit

 Current function  is ProgMpllSetup

 Current function  is ProgStaticDdrSetup

 Current function  is ProgStaticInitPerf

 Current function  is ProgStaticPwrClkGating

 Current function  is DUnitBlMode

 Current function  is ControlDDR3Reset

 Current function  is EnableVreg

 Current function  is ProgHmc

 Current function  is ProgReadWriteFifoPtr

 Current function  is ProgComp

 Current function  is SetIOBUFACT

 Current function  is ProgDdecodeBeforeJedec

 Current function  is PerformDDR3Reset

 Current function  is PreJedecInit

 Current function  is PerformJedecInit

 Current function  is SetDDRInitializationComplete

 Current function  is DisableRank2RankSwitching

 Current function  is MMRC_RcvnRestore

 Current function  is MMRC_WrLvlRestore

 Current function  is MMRC_RdTrainRestore

 Current function  is MMRC_PerformanceSetting

 Current function  is MMRC_PowerGatingSetting

 Current function  is MMRC_SearchRmt


                   . RxDqLeft RxDqRight RxVLow RxVHigh TxDqLeft TxDqRight CmdLeft CmdRight


Channel 0 Rank 0 . -20       18       -23     17     -26       23          0       0


CMD module is per channel only and without Rank differentiation

Current function  is ProgDraDrb

 Current function  is ProgMemoryMappingRegisters

 Current function  is ProgDdrControl

 Current function  is SetScrambler

 Current function  is ChangeSelfRefreshSetting

 Current function  is SetInitDone

 Current function  is McDisableHPET

 Current function  is FillOutputStructure


There is a treasure trove of information here, relating the stages of the boot process, the PEIMs being loaded, and the functions being performed. I’m at the point now where I can start relating all of this activity back to the original source code within the debug build I created with Visual Studio. Then use the SourcePoint debugger to single-step through the code and see its flow. It’s going to get even more exciting from here on in.

Check out Episode 7 and Episode 9 of The Minnowboard Chronicles!