[ANN] New free CPU module design

I was reading through the manual and noticed the following statement: System components CPU cards 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."?

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 interconnection.

Norm

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.

Regrads, Andras Tantos

Hi!

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 dominator.

- 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?

Regards, Andras Tantos