The SFF-SIG's philosophy is that new CPUs with PCI Express and USB expansion should be allowed to have ISA expansion as well.
After all, the embedded market is not forced to follow in the footsteps of desktop motherboards. This is great news
to the 70+% of the stackables market who still use one or more ISA I/O cards in their stack. The installed base of PC/104 ISA card users understand the tight coupling of application software to these I/O cards.
Against popular notions that the ISA bus is 'dead' due to the desktop PC market, the PC/104 I/O market is alive and well.
Rather than attempting to force the vast I/O ecosystem over to PCI, PCI Express or USB interfaces,
the SFF-SIG is offering an alternative: Replacing the parallel PCI bus with SUMIT™ while retaining the ISA bus (see the illustration to the right).
The ISA bus is easy to generate from the chipset's PCI or LPC buses. Furthermore, PCI Express is software-compatible with PCI, and PCI endpoint I/O controller chips are rapidly vanishing from the market. While SBCs and many PCI-based I/O cards are
reaching EOL (end of life) at an alarming rate, PC/104 ISA-based I/O cards are not, due to the use of CPLDs for the bus interface, and these CPLDs
are not caught up in the churn of the desktop PC primary market. Migration to new high-speed interfaces is now possible without re-engineering your ISA-based I/O cards and redeveloping and requalifying your software, thanks to SUMIT.
The majority of stackable CPU / SBC manufacturers located in the US already have one or more SUMIT-expandable platforms, most of which also include
the PC/104 ISA Bus. These include
ADLINK (Ampro), and others.
But board manufacturers without a significant presence in the US are still slow to realize that US System OEMs continue to seek CPUs that plug into their
I/O cards. In fact, System OEM designs are already finished which account for thousands of SUMIT-expandable CPUs to be shipped in 2012, just due to allowing existing proven ISA cards to plug in directly. Other board vendors need to invest now or miss the rapid growth.
To find SUMIT-based products, refer to the bottom of the SFF-SIG's
for a searchable database of current CPU / SBC and I/O products.
PC/104 I/O cards like the one shown to the right can plug directly into the CPU / SBC above
without the need for a PCI-ISA bridge card since ISA is supported directly on the CPU. Any PC/104-Plus (PCI) I/O cards such as Ethernet can be replaced by a SUMIT-ISM™ Ethernet card (NIC) which
passes the PC/104 Bus up the stack. Note the side benefit of extending overall system lifecycle since the PCI endpoint devices are mostly EOL already.
After all of the SUMIT™ cards are stacked, then ISA I/O cards are added on top. Although very few legacy stackable applications need the speed of PCI Express, rapid
obsolescence of PCI endpoint devices (ICs) combined with the disappearance of parallel PCI from the new 2011 chipsets are forcing this transition. Luckily, this change is transparent to application software.
Now that System OEMs have stockpiled 386SX, 486DX, Elan, and 5x86 CPUs / SBCs, it is time to consider the next migration step
which is as seamless as possible to the software, qualification, field trial and certification/regulatory processes.
As shown to the right, a typical Atom Z-series PC/104 CPU comes with an ISA connector to accomplish those goals, and even better, a SUMIT-A connector
is added to 'future-proof' the system, with a PCIe x1 lane, up to 4 USB 2.0 channels, LPC bus, I2C and SPI through the tiny connector.
At a slightly higher performance class, Geode GX processors join the ranks of Pentium MMX/II/III and Celeron processors as EOL. with
Geode LX processors still have several years left before EOL, but now is a good time to start planning the transition and evaluating
SUMIT-based SBCs. As shown, the PCI-104 (PC/104+ = PC/104-Plus) connector is replaced by a single 52-pin SUMIT-A connector. Since
graphics controllers are integrated into the chipsets now, and LAN ports are available on Atom Z-series and N-series PC/104 CPUs,
there are very few needs for high-speed peripherals at this middle performance class.
Atom N-series processors are the ideal replacements for the popular but EOL 855 chipset platform (with Pentium M / Celeron M processors).
In many cases, the EOL stacks used up to 3 or 4 bus master PCI devices, and a single PCIe x1 lane is not enough to cover all of the
high-speed I/O. Fortunately, the SUMIT architecture scales up nicely with a second connector, SUMIT-B, with 5 more PCIe x1 lanes. Together,
SUMIT-AB contains 6 PCIe x1 lanes with more clocks than computer-on-module (COM) architectures and certainly more than covering the
4 PCI bus masters A-D. In addition to PCIe lanes, SUMIT features easy-to-connect interfaces including 4x USB, LPC, I2C and SPI. Additional chipset I/Os
are not necessary to bring up the stack, since SUMIT is not a COM type, and due to SUMIT's minimal use of board space, there is ample
board space on the host to bring out its storage interfaces and serial ports rather than incur extra connector cost many times over.
Although very few stackable applications demand multi-core CPUs due to excessive heat and cost constraints, there have been a few
PC/104-size CPUs introduced which will become EOL in the next 3-5 years. Rather than tying up cash with last-time buy inventory, earn the
respect of your purchasing department by transitioning to the latest CPUs before the dreaded EOL notice arrives, reducing the EOL purchase to zero.
As shown to the right, this migration is as easy as the two above due to the inherent software compatibility of PCI and PCIe.
The PC/104 bus is secure through 2020 and beyond. The key reason is that components on these real-world I/O cards are not EOL.
Additionally, new CPUs with PC/104 ISA expansion are being introduced at the rate of 10-15/year based upon the latest Atom- and Core-series processors; each
CPU having a lifecycle commitment of 7+ years. PCI Express cannot replace ISA within the same cost and power envelopes, and LPC, USB,
I2C and SPI cover that low- to middle-data-rate space quite well. Real-world I/O chips such as A/D converters have native SPI interfaces,
for example. Shown to the right is the ideal flexible new CPU, with 3 additional mounting holes to support Pico-I/O modules as well as
SUMIT-ISM and PC/104 modules. The processor and chipset can be on the bottom surface with a heatspreader, and the I/O stack and pin
headers are conveniently accessible on the opposite site. It's no longer necessary to have a CPU in the middle of the stack, especially
having the higher thermal design power (TDP) processors in an MTBF-reducing restricted-air-flow environment.