...generally based on 1GHz Allwiner A10 chips, which are built around the ARM Cortex A8. While the chips carry out memory access operation tens of a percent faster than the Pi, Upton says their floating point operation and multimedia performance is far worse.
"If someone came along with something that was based on a good, fast AP [ARM processor] at $50 then I would be very concerned," he said.
"There's a number of people out there who market these boards saying 'Three times the performance of the Raspberry Pi'. I can't find a single benchmark that runs at that.
"I do find it annoying that people, and sometimes the manufacturers, naively claim that they're faster than the Pi when in practice they aren't."
The Foundation prides itself on the Pi being an open platform that offers completely open-source drivers for the ARM-based chip at its core. Being open — allowing anyone to rework software from the drivers up — is key to the Foundation's ethos of encouraging kids to take technology apart to see how it works.
"My view is where we've got to is sufficient to give people the goals of free software, which is for you to have control over what your machine does" — Eben Upton
However the Pi is not viewed as an open system in all quarters. A recent criticism of its open-source credentials was that the firmware for the GPU on the Pi's Broadcom chip is a closed-source blob, and not open to anyone outside of Broadcom to peruse or rewrite it. While the GPU driver might be open source, critics claim it operates at a high level and does very little of the heavy lifting, describing it as "little more than a message passing shim". Some tweaks to extend the Pi's graphical capabilities, for example adding new OpenGL features, cannot be carried out by modders as they would require access to the GPU's closed-source firmware, it was claimed.
The decision to base the Pi on the ARM architecture has also been called into question by those who decry the lack of publicly available documentation for the ARM core and its extensions, and the difficulty they say this causes in tasks like porting open-source VMs. From the point of view of being able to learn about the hardware and hack into it, these critics argue that open chip architectures like the LatticeMico32 would have been a better choice.
Upton says he struggles to understand the level of criticism by some members of the open-source community.
"I was a little bit disappointed that people were unhappy. I thought we'd taken a useful step in the right direction," he said.
"We have got to a point where everything on the ARM is open source and that is a new thing. Ninety-five percent of people gave us credit for doing what we could. People who are porting OSes are finding it useful, it accomplishes many of the goals of wanting to have free software," he said.
Upton believes the platform is as open as it can be, given the need of companies like Broadcom to protect their intellectual property — the designs of the underlying chip architecture — and also questions the pragmatic benefits of making the platform this open.
"It would be lovely if we distributed the source for everything, including the firmware and the documentation for all of the registers. I'm not quite sure I can understand the benefit it would bring to the community," he said.
"We and Broadcom put an enormous amount of effort where we could do that level of open source. I would like to open more stuff up but it's going to be tough. If you can't articulate a tangible commercial benefit to the IP holder, the person who has borrowed money from their IP investor, then you are on a hiding to nothing.
"My view is where we've got to is sufficient to give people the goals of free software, which is for you to have control over what your machine does."
He jokes that he is tempted to test the Pi's critics' commitment to having an open-source GPU.
"I'm tempted to do a Kickstarter and say 'I'm going to produce an open-source GPU'. I want $2m from all the people who've criticised me," he said.
The legacy of the Pi
The popularity of the Pi doesn't come without a cost. Upton and his wife Liz, who handles the PR for the Foundation, have bounced from helping to run the organisation to doing media and building the Pi community since the computer launched in February last year.
"I came out of an MBA programme directly before launching the Pi, so I had no time before and now I have also have no time," jokes Upton, who also works full-time.
"I'm very busy but it's good busy. Of course there have been bad days, like when we found out we had to CE test it and we'd built 2,000 boards and didn't know whether they were going to pass."
Despite the personal cost of being involved with the project, Upton says he believes in the Foundation too much to not stay around for at least another product launch.
"I'd like to take one more trip around the bay with this. We've got a really strong team, there's Pete Lomas who's our hardware guy and a very strong software team, both inside Broadcom and at The Computer Lab in Cambridge," he said.
Just as many of today's software engineers have fond memories of the Acorn BBC Micro and crafting their first BASIC program in the 1980s, Upton hopes the Pi might win a similarly treasured place in the hearts of engineers of the 2030s.
"I would like there to be some engineers who got their start with the Pi, who have a dusty old Pi in the attic that they will get down one day to see if it still works and reminisce about it," Upton said.
"I would like it to be remembered in the same way I remember the BBC Micro."