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回复: [edk2-discuss] Does warm reset clear DRAM?

gaoliming
 

Chipset may support the special reset with power on memory. This reset can keep power of DRAM, then DRAM content can be kept.

On capsule update, chipset will trig this reset. After reset, next boot is capsule update boot mode. It can get the updated capsule image from memory,
then do capsule.

Thanks
Liming

-----邮件原件-----
发件人: discuss@edk2.groups.io <discuss@edk2.groups.io> 代表
Konstantin Aladyshev
发送时间: 2022年9月4日 19:25
收件人: discuss <discuss@edk2.groups.io>
主题: [edk2-discuss] Does warm reset clear DRAM?

Hello!

I was reading about UEFI capsule update, and as I understood it
correctly OS saves new BIOS image into DRAM and passes a pointer to
the new image via NVRAM variable. Then the OS causes system reset.
BIOS in PEI stage sees the NVRAM variable and gets data from DRAM for
update.
I'm confused with this mechanic. Doesn't the system reset clear DRAM
content?
Even if it doesn't, doesn't the BIOS perform memory training at its
start? I thought that the memory training reads/writes patterns that
would mess DRAM content.

Best regards,
Konstantin Aladyshev
flb1972@...
 

This Capsule update actually issue a S3 reset.
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