Unxz image file

Embedded Linux Discussions
1

Hi Robert,

You have shown me the xz command to compress .img file to reserve the partitions in my previous topic.

xz -T3 -z -8 filename.img

Are there special options needed to decompress unxz back to .img with partitions? Or please show me the direct command that pipe into dd ?

Best Regards,
David

2 
xzcat filename.img.xz | sudo dd of=/dev/sdb

Regards,

3

Thank you very much!
David

4

Hi Robert,
I found using xzcat decompress pipe to dd is very slow. Probably decompress it before dd is a faster way.

Best Regards,
David

5

I found there are other dd-like tools, such as dcfldd, dc3dd, etc. Would you like to give me some suggestions that which is a better tool, or a faster one? Or some advice that to improve the flashing?

Best Regards,
David

6

Hi @dzhou dd is an exact bit by bit copy… Anything faster will be skipping sections, or optimizing the writing of the drive.

Either use dd (as a low level tool), or balena-etcher as a fancy gui…

Regards,

7

Hi Robert,

Thank you for your input and help.

Best Regards,
David

8

Hi Robert,

I found that dd with 8K buffer can write at 19.7MB/s. Save 50s over 3.8G image. (The one on Octavo Dev board with sanDisk emmc 32G)
I checked Kingston EMMC04G-M627 on BBBw, it is a little slower. But Datasheet indicates it can go 50MB/s writing with 8Bits databus. I guess BBBw is using 4Bits Databus. If so, not sure it can use 8Bits with an update of driver?

Best Regards,
David

9

This is incorrect, and common misconception… It’s running on a 8-bit bus.

Regards,

10

Hi Robert,

Sorry, I slipped my memory a little bit. I checked again that the emmc is 8bits:

pinctrl-0 = <&emmc_pins>;
bus-width = <8>;

The SD card seems 4Bits databust:

Device: OMAP SD/MMC
Manufacturer ID: 3
OEM: 5344
Name: SC32G
Bus Speed: 48000000
Mode : SD High Speed (50MHz)
Rd Block Len: 512
SD version 3.0
High Capacity: Yes
Capacity: 29.7 GiB
Bus Width: 4-bit
Erase Group Size: 512 Bytes

Best Regards,
David