Status Update on LS1028A Open Hardware CPU Module

The LS1028A CPU Module is an Open Hardware SOM (System-on-Module) developed as a joint venture between RBZ Embedded Logics, Madrid and MNT Research, Berlin. RBZ designed the electronics of the module. The project receives funding by the NLnet Foundation. Today we are demonstrating a functional prototype of the module integrated into the MNT Reform Open Hardware Laptop.

Why is the LS1028A Module interesting for Open Source?

• The module proves that MNT Reform's CPU and RAM are in fact upgradeable.
• While the MNT Reform laptop is Open Hardware conforming to the OSHWA definition, the default i.MX8M SOM (CPU/GPU/RAM module plugged into the motherboard) itself is not—(it has PDF schematics, but no design source files). This means that even if it is a standard part, there is only one supplier and third parties cannot independently reproduce the SOM. This changes with the LS1028A module: the design files are open source.
• The NXP LS1028A processor on the module can support 8GB or even 16GB of LPDDR4 memory instead of the 4GB of the default module.
• The DDR4 memory controller in the LS1028A does not need binary firmware to initialize, unlike the one in i.MX8M. The eDP (embedded DisplayPort) controller still needs binary firmware, but it is possible to construct a blob-free computer with respectable performance from the module using a simple 2D graphics chip or FPGA for the display output instead. This can be attractive for people seeking a computer that passes FSF RYF certification. Note that we used the integrated eDP controller in our MNT Reform tests.
• The LS1028A processor has 2 out-of-order Cortex-A72 cores instead of 4 in-order Cortex-A53 cores in the i.MX8M. While both chips run at 1.5GHz, quick benchmarks show that the single core speed of LS1028A is 1.5x-2.0x that of i.MX8M. (sysbench single thread speed: 1474.79 vs 738.25, stress-ng matrixprod test, 10s: 410 bogo ops vs 270).
• The LS1028A has a large address space for PCIe and can drive external GPUs.

Functional Prototype

RBZ built 6 SOMs in total and hand-fixed two of them for bringup purposes and then made a second revision of the design with bugfixes integrated. As of July 25th, 2022, we have a working MNT Reform laptop prototype utilizing the LS1028A module with 8GB LPDDR4. We have validated and brought up a sufficient number of features to have a useful system:

• 2x Cortex-A72 at 1.5GHz
• 8 GB LPDDR4
• UART, I2C
• SD card with u-boot and Linux kernel
• eMMC storage with Debian OS (MNT Reform System) on the SOM
• GPU with etnaviv open source drivers
• eDP display
• USB3.0 and USB2.0 integrated with motherboard hub, keyboard, trackball
• SAI Audio (to WM8960 codec on motherboard)
• Ethernet or WiFi via USB dongle
• Battery power via motherboard
• Hand-modified passive heatsink

Here are some shots and videos of popular applications running on the prototype:

TODO

• Update 2022-08-31: PCIe and SATA are up and running now. SERDES: LS1028A—like its Layerscape/QoriQ siblings—implements several high speed serial functions in a flexible SERDES engine with up to 4 lanes. In our case, we use the lanes for 2x PCIe Gen3, 1x SATA and SGMII Ethernet.
• Power/Heat: Expectedly, the LS1028A module consumes around 30% more power than the default i.MX8MQ module and also generates more heat when the CPUs are under load. While we hand modified the existing heatsink for adequate cooling in tests, we will design a larger custom heatsink for the final product.

Source Code / Design Files

• Hardware Design Files of LS1028A SOM and eDP adapter
• MNT Reform System Image Branch with RCW, ATF, Linux Patches

Interested?

We are looking for distributors and system integrators who would like to ship Open Hardware devices featuring the LS1028A SOM. Get in touch.