Skip to main content

jTagging along

Background story:
I wanted to create an appliance that simply allows one to listen to web radio and allows S/PDIF output. My idea was that using my old Dreambox DM500-T would be perfect for this - so I started hacking away.

I began with trying to customize and compile my own kernel using tuxbox as a base and mimicking one step after another until I finally had my own cross-compiler and Linux kernel that I could hack as much as I wanted.

Worth noting is that the built in bootloader in DM500 is accessed by pressing Enter a second after power-on. The bootloader allows transfer of the kernel to RAM from TFTP which means I don't actually needed to modify the flash in order to load a new kernel. As a final note, the bootloader is located in the same flash as everything else (uh-oh). A few hacks later and the built-in bootloader printed an error message and nothing else :-(.

Googling, googling and googling did not really produce anything of value except that when people had even more serious issues (no output at all) they resorted to JTAGing. I never had the pleasure of JTAGing and quite frankly I did not possess any knowledge worth nothing about the inner workings of JTAG either. Status: One bricked device and a opportunity to learn something I wanted to learn for a long time - excellent!


The DM500 board exposes 2x8 pads which needs to be soldered to wires in order to access the JTAG signals. JTAGing DM500 is not uncommon and there are quite a number of programs available to do so, but they are all ad-hoc and requires a DB25 to LPT-port. I did not like that solution very much, I wanted to use a real JTAG in order to learn how to do it "the right way".

Schematics of the the ad-hoc DB25 to JTAG was readily available which offered pin positions on the DM500 board of almost all JTAG signals - only lacking TRST and VCC reference.

I tried connecting the available JTAG signals to my ARM-USB-OSD but without luck, I wasn't really surprised since my adapter needs a Vref in order to know what voltage to output (nice feature, it makes burning things up so much harder).

Today during breakfast I discovered a czech forum post listing what I hope is the correct pinout for the whole 2x8 PAD, which means it should only be a matter of soldering the last two signals. If it works, I will upload complete schematics, BSDL (if needed), scripts and how-tos - that is a promise.

For reference, DM500 consists of an IBM STB02500 SoC with an Intel flash.

Comments

Popular posts from this blog

Buying an IBM Mainframe

I bought an IBM mainframe for personal use. I am doing this for learning and figuring out how it works. If you are curious about what goes into this process, I hope this post will interest you.

I am not the first one by far to do something like this. There are some people on the internet that I know have their own personal mainframes, and I have drawn inspiration from each and every one of them. You should follow them if you are interested in these things:
@connorkrukosky@sebastian_wind@faultywarrior@kevinbowling1 This post is about buying an IBM z114 mainframe (picture 1) but should translate well to any of the IBM mainframes from z9 to z14.

What to expect of the process Buying a mainframe takes time. I never spent so much time on a purchase before. In fact - I purchased my first apartment with probably less planning and research. Compared to buying an apartment you have no guard rails. You are left to your own devices to ensure the state of whatever thing you are buying as it likely…

Powering a mainframe

The last few days have been eventful. I was contacted by the datacenter that the mainframe's cage is now ready for moving in, and the power has been made available. Very exciting! I grabbed my home-made power cables (more on that later) and my best screwdrivers and set off to the datacenter.


The datacenter staff, not needing a forklift in their day-to-day, had managed to solicit the services of a forklift, the associated operator, and some very handy folks to help navigate the mainframe from the storage space to its final location.



After some intense period of fighting the inclination of the road between the storage facility and the cage (and a door that was a bit too small) it was finally in place. Incidentally we were forced to trust the wheels on this pretty rough floor. I did not expect it to roll that well on raw concrete, I was pleasantly surprised. This thing is a tank!

Now, everybody wanted to see if it was working. My machine did not come with a power cable so I had to so…

Open Datacenter Hardware - Leopard Server

Introduction The Leopard is an OpenRack v1 compliant 12V server commissioned by Facebook to offer compute power. It consists of 2x Intel Xeon E5-2678 v3 and is available with either DDR3 or DDR4 memory. The model is manufactured by two vendors primarily: Quanta and Wiwynn.

Leopard features a 24x PCIe slot which can fit either a PCIe card with low profile, or a riser card with 1x 16x and 1x 8x slots. The server also supports a 3.5" SATA drive as well as either an mSATA or an M.2 drive mounted on the motherboard.

Connectivity wise Leopard has a mezzanine card slot allowing for example 10Gb/s or 25Gb/s Ethernet.

Figure 1 and figure 2 shows the server layout. The server is made to fit inside an OpenRack v1 enclosure, at which point it looks something like figure 3. Due to power constraints an OpenRack v1 can fit 30 of these servers before power starts to become an issue. The Leopard servers that the organization Serverfarm Upstate provides are all fitted with 256GiB DDR3 RAM and 2x …