Resizeable Bar Support on the Raspberry Pi
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The article discusses the implementation of Resizeable BAR support on the Raspberry Pi, sparking a discussion on the technical details and implications of this feature, as well as other related topics such as PCIe limitations and USB-C power delivery.
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Generally, hobbies are activities where one sees loss not profit.
There's some truth to what you're saying. Even the smallest apartment I've ever had was big enough to dedicate space to some serious hobbies, and it was (at that time) very inexpensive to rent compared a much smaller place in a more-dense area.
My lifestyle isn't very compact because it has never needed to be compact. Compactness isn't a common expectation 'round these parts. I have space to keep collections of stuff that I find interesting, and to make use of it.
There's tradeoffs to this lifestyle, though. The corner store is only a short walk away, but it mostly just sells beer, soda, and smokes. There's no walking to get something like groceries, or a new shirt (or a used shirt, for that matter). There isn't much for local entertainment. It's 15 miles to the next-largest city, and there's zero public transportation aside from the buses that get kids to/from school.
(It's hard to imagine that there aren't areas of the UK that are of similar form, though, with roomy housing, space for things, and with very limited services and/or options for commerce nearby.)
In fact, I am walking to the grocery store as I dictate this to my phone
In terms of choice: No, not really. The housing market is very tight these days. So for now, at least: While I must live somewhere, I don't necessarily get to live where I want. I must instead make do with living where I can (and I suppose optionally also maintain hope for a better day tomorrow).
The UK settlement pattern is quite weird. About 1/6 of the population lives within the South-East, which is roughly the area commutable to London by train. Then another 1/6 of the population lives in London. So land is very expensive there. The rest of the UK is on average a lot poorer. So the UK in general is not conducive to large housing. You can certainly find old farm houses out in the sticks, and small villages that are mostly expensive large houses. These are a tiny fraction of the housing, though. I believe UK houses are on average the smallest in Europe. (I think the UK would benefit a lot from some decentralisation, but that's a different topic. Side eye in cancelled HS2 lines.)
[1]: https://assets.publishing.service.gov.uk/government/uploads/...
[2]: https://fred.stlouisfed.org/series/MEDSQUFEEMO
But to defend Jeff, the pictures in the article show like a 4x4 corner of a room, even if we extrapolate to say, 8x8x8, that amount of space can usually be found in even a 1-bedroom apartment. I have seen many pictures of amazingly complete electronics/hacking workbenches from around the world that easily fit into much smaller spaces.
Of course, the US has also done a lot more than many places to preserve natural wilderness with national and ngo parks/reserves.
My house in Phoenix, AZ, USA is relatively typical 3br/3ba and just over 2K sqft (around 192 M^2), and I know a lot of people with larger homes than this.
We operate one of the largest print farms in the nation, and I can count the number of human-scale or larger sculptures we've put out in the past decade on one hand.
"Perfboards", perhaps?
Why'd the capitalisation of BAR get lost between the article and here? It's a little triggering.
Other than that, nice to see, a lot of ARM SoCs & SBCs have asininely small PCIe memory map sizes. Looking at you, RK3399, what was it, 64MB? Not even enough for some NICs.
It is even entirely within spec for a PD power supply to offer a 5V5A PDO, as long as it is only doing so with a 5A capable cable (i.e. 100W or 240W). 5V5A is no more a fire hazard than 20V5A.
The spec violation isn't that it negotiates 5V5A when available, but that it isn't willing to buck from 9V or 15V to get those 25W which means that power supply compatibility is incredibly limited.
My pocket PD can request 5v5a from quite a few chargers in PPS mode.
With that said, DisplayPort Alternate Mode would be considerably more straightforward.
There is real cost savings here -- the RPi5 avoided the need for a buck circuit, and for that matter probably a dedicated PD controller chip.
In contrast, in the context of a "cheap vape pen" you have a battery which means you need to be able to convert to (and from!) battery voltage, so you need that conversion circuitry anyway.
Even the voltage is not matching spec (Pi power supply has 5.1 volts, not 5.0 volts!). That is because historically Pi had shitty cables, with high resistance and voltage drops. 5V5A is not even in spec, limit for 5 volts is 3 amps!
> fire hazard than 20V5A
That would be 100 watts! Many people just grab any usbc cable, and solder it directly to GPIO power pins. But good luck with that!
Initial batches of Pi4 did not even had a resistor, to request 3.0 amps!
The point is that power dissipation in a cable is a function of the current going through it. The cable will get exactly as hot carrying 5 amps with a voltage of 5 volts as it will carrying 20 or 48.
(now, that is more *wasteful* -- you lose the same amount of power to heat carrying 25W at 5V5A as you do at 100W 20V5A, but that's 4x the relative waste in power)
> Many people just grab any usbc cable, and solder it directly to GPIO power pins.
You're not going to get *any* 5 amp mode out of a standard PD power supply unless the cable indicates it is 5 amp capable, which isn't going to happen unless that "any usbc cable" has the right emarker on it.
> limit for 5 volts is 3 amps.
There is no such limit.
What there is is two things: 1. There are a standard set of PDOs a standard "X watt" PD power supply is supposed to provide. 5V3A 9V3A 15V3A 20V5A, (then 28, 36, and 48 volts for EPR) with the highest one limited to the power limit of the supply. These only go up to 3 amps until you get to 20 volts. 2. Devices are supposed to support those standard PDOs.
Anything other than those standard PDOs is optional (at least before 3.2 which starts introducing AVS as a requirement at 27W+). 12V support is common, as for that matter is PPS support. 5A support below 20V in fixed PDOs is 100% allowed but is super rare.
(5A lower voltage PPS is a different story, but unfortunately the RPi5 doesn't know how to negotiate 5V PPS. That is a shame because it would 100x its power supply compatibility because most chargers targeting higher end Samsung phones support it.)
A power supply is 100% allowed to support 5V5A. It just isn't required to. It would have been 100% legitimate for the RPi5 to have a buck circuit to handle a standard 27W 9V3A power supply and then turn that buck off if the power supply and cable support 5V5A.
> Initial batches of Pi4 did not even had a resistor, to request 3.0 amps!
To be precise, it had *a* resistor (connected to the shorted together CC pins) when it was supposed to have one separate resistor for each pin, and that broke cables with emarkers.
sigh
It’s ok for small things but even once you get into the command buffer range it’s slow slow slow without dma.
Lengths of BARs have to be powers of two.