WYSE thin client Reverse Engineering

  The ROMs:      VSA Init ROM:  (Virtual Systems Architecture)  is a piece of software that is hiding the real hardware from the OS and is emulating standard hardware like keyboard controller, IDE controller, CMOS and other legacy hardware.       The Geode, rather than carrying lots of legacy hardware interfaces that are presumed to exist on x86 systems that might be painful to implement on a highly integrated, low power processor, the Geode often emulates such interfaces by use of software that is invoked by special traps that take place when the processor accesses these devices.     This emulation is made at the hardware level by setting some Model Specific Registers (MSRs) that control the GeodeLink Interface Units (GLIUs). This GLIUs can trap CPU access to some defined memory regions and run some ISRs from VSA software instead, or route the access to some other devices. VSA system is a TSR software(Terminate and Stay Reside...

     A few months ago I've bought this WYSE thin client model Sx0 - S50. I wanted to make a retro game machine from it but soon I've realized that I can't make it boot from the DOM with MS-DOS 6.22.      This was interesting because the system was able to boot MS-DOS 6.22 from a USB memory stick. So I've started to investigate the cause for this.      On the first hardware inspection I’ve found a small memory chip on the back of the PCB, an 8 pin SOIC EEPROM “ 93C46A ” that is not bigger than 128 bytes. I’ve dumped the content of this chip using the CH341A (mod-ed to read 93C chips) and all I’ve found was the serial number of the machine: 6IFDGB03427.  You can find the contents of this chip in  here .      Then I’ve start to read more, searched all the internet for documents that might help me understand this machine, and I’ve found some that I’ve put in here .         There you can find docu...