I finally had the time to publish my latest work on my website: it is a
small 32-bit ARM-based CPU card that is supposed to be the first one in a
series. I named the design concept H-Storm, and it will contain CPU modules,
peripherials and system boards. The design is open and free (for
non-commercial uses) so both the schematic and the PCB can be downloaded.
Please take a look and comment!
The web-page is: http://h-storm.tantos.homedns.org .
BTW: I'm thinking of creating a number of these modules for sale, but to
calculate the price it would be nice to now the volume. So if you might be
interested in buying one instead of building your own, let me know.
I was reading through the manual and noticed the following statement:
In every H-Storm system there’s at most (and usually) one CPU card.
Is that a typo - "...at MOST (and usually) one CPU CARD."?
Thanks for the comment. Well, it's not a typo, but my wording might be a bit
unclear: every such system has to have a CPU *somewhere* but nothing
prevents you to build a CPU board and plug peripherial cards into it. In
such a system there is no *CPU card* in the sense that H-Storm identifies
It looks like your System Board can accommodate at most one CPU card and one
Peripheral card. That's marginally not enough even for most hobbyist
projects. If you have any commercial aspirations, you'd better redesign
your "bus" so that it's extensible using stuff from commonly available
sources. If you want a simple example: Although it has nothing [at least
nothing necessarily] in common with a PC, an ISA bus makes a wonderful
system interconnect device that's commonly available in 2-20 slot
configurations called passive backplanes. You could easily add polarizing
keys and slots to prevent inserting a normal PC card. There are other more
general, commercially available backplanes that can be used for system
Thanks for the comments. It might have been unclear from the web-site, but a
system board can accommodate up to three peripherial cards (usually it would
be two since some peripherial functions would be on the system board
itself). The *particular* system board I had time to finish and document has
indeed only one peripherial socket.
There were many reasons for this limit of three peripherials. One is the
number of pins I wanted to use. The second is that many CPU/MCUs out there
are capable of addressing around this number of external peripherials. Yet
another reason was that I wanted to limit the capacitive load on the bus to
simplify system integration.
There are a number of important differences between my 'bus' and the ISA
bus, though I sure have examined it before coming up with my design:
- In H-Storm there's a separate module-select signal for each module. On the
ISA bus each card has to have its own address decoder logic.
- In H-Storm there are dedicated IRQ lines for each module, while on the ISA
bus each card has to have its own IRQ select logic.
- H-Storm doesn't support (at least in the standard version) DMA
operations. - This is due to the fact the most of the CPUs I intended to use
don't support it.
- H-Storm has 3V I/O, while ISA is 5V. - 5V compatibility as a requirement
would have limited the available components considerably.
- H-Storm allows for different bus-timing for each peripherial. ISA does not
have this feature, meaning you have to operate on the least common
- The H-Storm form-factor is significantly smaller than the ISA form factor.
- H-Storm defines a two-wire (I2C) side-band bus that can be used for
configuration and PnP information retrieval. That's no such concept in ISA
(PCI has something similar).
With all that, most ISA bus peripherial ICs that are available in 3V
versions should be fairly simple to interface with the H-Storm bus. One
example would be the CS8900 ethernet controller.
Most of the decisions above stem from the desire to simplify module design
and system integration.
While I agree that the ISA bus is a very usable interconnect for many
embedded applications, there are cases when something, like H-Storm fits the
bill better. What other backplane designs do you have in mind that you think
would make a more direct comparison?
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