Loongson 3B1500 (LS3C-2WAY-SERVER) Motherboard

Loongson 3B1500 Dual Development board (龙芯3B1500双路开发板 [archive.org]) uses two Loongson 3B1500 processors and AMD RS780E+SB710 chipset. The board is also referred to as 龙芯3B05+RS780E双路开发板 or 3B1500780E双路评估板 in newer documents. Loongson is a series of system that are designed in China. GODSON is the academic name for the Loongson processors. This family of processor implements MIPS instruction set [1].

The motherboard has standard Extended ATX (E-ATX) mounting holes and can be installed in commodity PC chassis. I like how they keep unnecessary costs down this way. I went one step further and installed it in an ATX chassis (Corsair Carbide 400Q) with smaller number of mounting screws. So far it's working, but I cannot recommend anyone else to do the same.

The sticker on DIMM says HXMSH8GP13A1F1V-13H 8GB, 2RX8, PC3-10600P-999. These memory modules appear to be standard DDR3-1333 1.35V/1.5V Registered ECC DIMMs.

Firmware

The firmware is called PMON2000. It has both CLI and BIOS Setup-like menu. The Loongson BIOS Setup says that the processor is GODSON3 @ 1000 MHz. While the BIOS Setup only recognizes 16 GBytes of memory on the first node, the Linux kernel recognizes the full 32 GBytes of memory.

The firmware refused to load any kernel saying attempt to load into mappable region until we updated the PMON to latest build of 3.3. Latest firmware for this board is found on 3B780E1500双路开发板 [archive.org]. PMON update procedure is found on PMON编译方法 [csdn.net].

Operating System

The Loongson Linux is found on Loongnix系统 [loongnix.org]. The Fedora21-MATE 20150815-Release works fine on this board.

• /proc/cpuinfo
• dmesg
• /proc/interrupts
• /proc/iomem
• /proc/ioports
• lspci -vnnt

As seen on the diagnostics messages above, only 15 processor cores are available to the user. The motherboard is a two-socket system, so it is odd to have an odd CPU count (naturally).

Installation Notes

There were following issues when installing Fedora-MATE-Live-5.iso image on 2017-Jan-07.

• Firmware doesn't accept path like (cd0,0)/boot/vmlinuz
  • Cannot boot from installation media (boot.cfg doesn't work)
  • The system can be manually bootstrapped with following three steps in the PMON> prompt:
    1. load /dev/fs/iso9660@cd0/boot/vmlinuz
    2. initrd /dev/fs/iso9660@cd0/boot/initrd.img
    3. g root=live:LABEL=Fedora-MATE rootfstype=auto ro rd.live.image
  • The same issue applies to the installed system. I needed to modify the boot.cfg. The filesystem path for the first SATA direct-attached storage device was /dev/fs/ext2@wd0/, even though it was an ext3 filesystem.
• Firmware doesn't accept symbolic links in the boot partition
  • The firmware looks for /boot/boot.cfg on the first partition of the boot disk
  • The /boot directory needs to be a real directory; if it is a symbolic link, the firmware fails to find the boot.cfg
  • This happens to be the case when the Fedora image is installed in the default setting.
• The coin battery (CR2032) must have sufficient voltage.
  • The Linux kernel itself appears to work alright, but after going multi-user, the system hangs up occasionally when the battery is dry.
• One of the Ethernet ports must be connected for Power-on Self Test (POST).
  • Maybe it's just me or the specific PMON version that I'm using, but it appears that one of the Ethernet ports must be linked-up for the POST to pass. Without the Ethernet cable, the video output from the VGA port does not come up. FYI: In Fedora, the port that is closer to the board is the primary one, and the other port that is farther from the printed circuit board is the secondary one.
• The firmware recognizes USB keyboard or USB direct-attached storage device.
  • But it appears that only one device is recognized at most. You cannot use USB keyboard and USB direct-attached storage device simultaneously.
  • Use commands like load /dev/fs/fat@usb0/vmlinuz to load image from the USB direct-attached storage device.
• Debian bullseye and bookworm debian-installer kernels does not boot on this motherboard.

References

1. W. Hu, L. Yang, B. Fan, H. Wang and Y. Chen, An 8-Core MIPS-Compatible Processor in 32/28 nm Bulk CMOS, in IEEE Journal of Solid-State Circuits, vol. 49, no. 1, pp. 41–49, Jan. 2014.