Show HN: I built an open-source Linux-capable single-board computer with DDR3

Re:Show HN: I built an open-source Linux-capable single-boar... by peter_d_sherman on Thursday December 25, 2025 @12:18AM (#46382269)

Very cool!

A few questions:

How was the 696 MHz DDR3 RAM speed determined?

Also, how is the system initialized at startup? Is there boot/startup code, does that exist in a flash chip (or some other ROM or EEPROM or flash type chip) on the system, and can the boot code be inspected/customized/overwritten by the end-user? How does the system boot?

Anyway, looks very cool!

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Re:Show HN: I built an open-source Linux-capable single-boar... by Cyao on Thursday December 25, 2025 @02:41AM (#46382868)

Thanks! I used the orange pi pc fel tester [1] and gradually lowered the clock speed until it became stable. When I got to 696 MHz the test ran for more than 3 hours without problems.

The H3 CPU has a small bootloader inside, that enumerated the SD card and eMMC to look for a user-made bootloader. IIRC it looks for some file inside of the file system, and loads it to 0x70000. Thus you can customize it if you have enough time :)

[1] https://github.com/ssvb/lima-memtester/releases/tag/20151207...

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Re:Show HN: I built an open-source Linux-capable single-boar... by peter_d_sherman on Saturday December 27, 2025 @12:08PM (#46403222)

Interesting, and very cool!

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