Sandy Bridge Raminit

Introduction

This documentation is intended to document the closed source memory controller hardware for Intel 2nd Gen (Sandy Bridge) and 3rd Gen (Ivy Bridge) core-i CPUs.

The memory initialization code has to take care of lots of duties:

  1. Selection of operating frequency
  • Selection of common timings
  • Applying frequency specific compensation values
  • Read training of all populated channels
  • Write training of all populated channels
  • Adjusting delay networks of address and command signals
  • DQS training of all populated channels
  • Programming memory map
  • Report DRAM configuration
  • Error handling

Definitions

Symbol Description Units Valid region
SCK DRAM system clock cycle time s  
tCK DRAM system clock cycle time 1/256th ns  
DCK Data clock cycle time: The time between two SCK clock edges s  
timA IO phase: The phase delay of the IO signals 1/64th DCK [0-512)
SPD Manufacturer set memory timings located on an EEPROM on every DIMM bytes  
REFCK Reference clock, either 100 or 133 Mhz 100, 133
MULT DRAM PLL multiplier   [3-12]
XMP Extreme Memory Profiles    

(Inoffical) register documentation

Read training

SMBIOS type 17

The SMBIOS specification allows to report the memory configuration in use. On GNU/Linux you can run # dmidecode -t 17 to view it. Example output of dmidecode:

Handle 0x0045, DMI type 17, 34 bytes
    Memory Device
	Array Handle: 0x0042
	Error Information Handle: Not Provided
	Total Width: 64 bits
	Data Width: 64 bits
	Size: 8192 MB
	Form Factor: DIMM
	Set: None
	Locator: ChannelB-DIMM0
	Bank Locator: BANK 2
	Type: DDR3
	Type Detail: Synchronous
	Speed: 933 MHz
	Manufacturer: 0420
	Serial Number: 00000000
	Asset Tag: 9876543210
	Part Number: F3-1866C9-8GSR
	Rank: 2
	Configured Clock Speed: 933 MHz

The memory frequency printed by dmidecode is the active memory frequency. It’s not the double datarate and it’s not the one encoded maximum frequency in each DIMM’s SPD.

Note: This feature is available since coreboot 4.4

MRC cache

The name MRC cache might be missleading as in case of Native ram init there’s no MRC, but for historical reasons it’s still named MRC cache. The MRC cache is part of flash memory that is writeable by coreboot. At the end of the boot process coreboot will write the RAM training results to flash for future use, as RAM training is time intensive. Storing the results allows to boot faster on normal boot and allows to support S3 resume, as the RAM training results can’t be stored in RAM (you need to configure the memory controller first to access RAM).

The MRC cache needs to be invalidated in case the memory configuration has been changed. To detect a changed memory configuration the CRC16 of each DIMM is stored to MRC cache.

Note: This feature is available since coreboot 4.4

Error handling

As of writing the only supported error handling is to disable the failing channel and restart the memory training sequence. It’s very likely to succeed, as memory channels operate independent of each other. In case no DIMM could be initilized coreboot will halt. The screen will stay black until you power of your device. On some platforms there’s additional feedback to indicate such an event.

If you find dmidecode -t 17 to report only half of the memory installed, it’s likely that a fatal memory init failure had happened. It is assumed, that a working board with less physical memory, is much better, than a board that doesn’t boot at all.

Note: This feature is available since coreboot 4.5

Try to swap memory modules and or try to use a different vendor. If nothing helps you could have a look at chapter [Debugging] or report a ticket at [ticket.coreboot.org]. Please provide a full RAM init log, that has been captured using EHCI debug.

To enable extensive RAM training logging enable the Kconfig option DEBUG_RAM_SETUP

Lenovo Thinkpads

Lenovo Thinkpads do have an additional feature to indicate that RAM init has failed and coreboot has died (it calls die() on fatal error, thus the name). The Kconfig options H8_BEEP_ON_DEATH H8_FLASH_LEDS_ON_DEATH enable blinking LEDs and enable a beep to indicate death.

Note: This feature is available since coreboot 4.7

Debugging

It’s recommended to use an external debugger, such as serial or EHCI debug dongle. In case of failing memory init the board might not boot at all, preventing you from using CBMEM.