Lexra did implement a 32-bit variant of the MIPS architecture. Noteworthy architectural feature was the lack of the MIPS I instructions
lwl, lwr, swl and
swr that optimize the handling of unaligned loads. Later the LX4580 core added hardware multithreading. Products implementing Lexra's architecture include the LX4080, LX4080P, LX4180, LX4280 and LX5280, LX8000. Today Lexra is a defunct company. Several key employees of Lexra founded the digital video core company Ultra Data Corporation, the intellectual property assets of which have since been acquired. Many other key Lexra employees, including co-founder and CEO, Charlie Cheng, now work for ASIC vendor Faraday Technology in Taiwan, Sunnyvale, CA, and Framingham, MA. Lexra co-founder and CTO Pat Hays is now vice president of engineering for MIPS Technologies, Inc. in Mountain View.
Jonah Probell has written a history of Lexra
lwl, lwr, swl and
swr are covered by US patent 4,814,976. Lexra therefore choose to implement these instructions by software emulation. In the 1999 - 2002 lawsuit of MIPS Technologies, Inc. vs. Lexra, Inc. about violation of this and a second patent, Lexra and MIPS reached an agreement and the court never ruled on the matter. Which means it isn't clear if Linux can or cannot legally emulate the instructions.
Instructions emulator sourcecode from Lexra exists as Linux MIPS kernel patches and available under GPL license.
Technically support for Lexra processors without adding emulation of these instructions would be possible but the question is how much sense it would make as some software may rely on it fairly heavily.
Following the lawsuit Lexra became a MIPS32 license. MIPS later acquired Lexra's IP. This resulted in the end of Lexra's former products and so at this time there also seems to be little interest in actually adding Linux support.
The Realtek RTL8181 is a highly integrated System-on-a-Chip with a high-performance 32-bit RISC microcontroller, two Ethernet MACs and a WLAN controller embedded onto a single chip. RTL8181P BGA version has a PCI Bridge which supports one external PCI/MiniPCI device.
The embedded Lexra LX5280 32-bit RISC CPU runs at up to 200MHz and features separate 8KB instruction and data caches.
- RTL8181 description
- RTL8181 DataSheet
- Linux on Realtek RTL8181
- RealAP - Linux mini-distribution for RTL8181 based devices
Devices are based on the RTL8181:
- Known RTL8181-based consumer devices
- Edimax PS-1205UWg print server
- Edimax EW-7206APb
- Edimax EW-7207APb
- Edimax BR-6104WB
- Minitar MNWAPB 902.11b AccessPoint
- Minitar Hacking
- Minitar firmware sourcecode: sdk-1.4, sdk-1.6
Most of the RTL8181-based devices comes with a simply bootloader and Linux as firmware. See a Minitar sourcecode and RTL8181-linux project. Seems, RTL8181 shares some code with ADM5120. Both they use CSYS header format and some applicatinos (i.e. setup), but RTL8181 firmware is Big-Endian.
RTL8181 supports JTAG and MIPS EJTAG 2.0:
- ManufID: 6
- PartNumber: 5280
Don't confuse the RTL8181 with the RTL8180. It's just plain WLAN chip, that also happens to be the one embedded on the RTL8181.
- US Patent 4,814,976
- MIPS Technologies, Inc. press release about the Lexra case
- LX5280 at webarchive
- LX4180 at webarchive