Author Topic: 8-bit uC - is there even a point?  (Read 24419 times)

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Offline technix

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Re: 8-bit uC - is there even a point?
« Reply #400 on: October 11, 2018, 05:32:12 pm »
Sure. An actually small 32 bit ARM such as the Cortex M0 or a simple 32 bit RISC-V would be appropriate to compare to the likes of Z80.

It's hard to know much about ARMs but in fully open RISC-V land you have for example https://github.com/SpinalHDL/VexRiscv which can be configured as RV32I at 346 MHz and 0.52 Dhrystone MIPS/MHz on an Artix 7 using 481 LUTs and 539 FFs.

LUTs don't convert conveniently to equivalent gates, but somewhere between 6 and 24 is about right, and probably 12 is a good average. So that's somewhere between 3000 and 12000 gates for the LUTs with 6000 probably being a good guess. D flip-flops are worth 4 gates each I guess, so that's 2000. Total maybe 8000.

Physically a LUT consists of 64 config bits which are selected by 6 address lines. Thus it's 63 muxes, which is lot more than 12 gates. You may be able to get the same effect with discrete gates, or you may be not. It's like data compression - some data compresses well, some data doesn't compress at all. You only can tell, if all 6 inputs are used, you need at least 6 gates. Therefore comparing LUTs to gates is not a good idea.

If you compare to FPGA based cores, such as Picoblaze, your basic RV32I is equivalent of 5 Picoblazes (however I don't think Picoblaze can run at 350 MHz).

However, this is a very basic, very feeble processor. If you start adding features (look at the table you posted: https://github.com/SpinalHDL/VexRiscv ), by the time you add enough features to make it into a typical 32-bit processor, you get to 2000 LUTs and the speed deceases to 183 MHz - now it's equivalent to 20 Picoblazes and your RISC is now running slower than Picoblaze.

This is a very interesting table, by the way - adding features consumes lots of logic, but performance growth is not great - your fastest RISC is not even 50% faster than the feeble 346 MHz model.

And that's RISC - the best 32-bit CPU the humanity could come up with. If you look at others (such as ARM or Microblaze), the pattern will be the same, but the performance will be even lower.
There is a certain thing 8-bit processors suffer: memory space. Certain programs eat RAM like candy (Google Chrome with more than a handful of tabs open) and 8-bit cores will quickly start to suffer even if it has 64-bit memory pointers.

Note that the 32 bit ARM1 is listed on the Wikipedia page you referenced as having 25000 transistors, about 3x the z80.

If we use the smallest 32-bit processor (ARM1), shouldn't we pick the smallest 8-bit processor for comparison? The table shows 3500 transistors for 6502. Your ARM1 is roughly 7 times bigger.
Do keep in mind that one NMOS transistor can map to multiple CMOS transistors. The 25000 CMOS transistors in ARM1 and the 3500 NMOS transistors in 6502 maps to ARM1 having about three times the gate count.
 

Offline Fungus

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Re: 8-bit uC - is there even a point?
« Reply #401 on: October 12, 2018, 07:23:52 am »
Are there any 3 cent 32 bit microcontrollers?   >:D

There won't be any ARM chips, the ARM royalties will be more than 3 cents.
 

Offline mikeselectricstuff

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Re: 8-bit uC - is there even a point?
« Reply #402 on: October 12, 2018, 08:10:44 am »
Are there any 3 cent 32 bit microcontrollers?   >:D

There won't be any ARM chips, the ARM royalties will be more than 3 cents.
RISCV?
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Offline rjp

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Re: 8-bit uC - is there even a point?
« Reply #403 on: October 12, 2018, 08:24:53 am »
Are there any 3 cent 32 bit microcontrollers?   >:D

There won't be any ARM chips, the ARM royalties will be more than 3 cents.
RISCV?

Not until someone is producing them in the numbers that get economies of scale.

Id expect one of the Chinese mobs to be on to that sooner rather than later but its not today.
 

Online GeorgeOfTheJungle

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Re: 8-bit uC - is there even a point?
« Reply #404 on: October 12, 2018, 10:07:29 am »
Are there any 3 cent 32 bit microcontrollers?   >:D

How about 1 cent, and flexible?

$0.01 Flexible Plastic ARM Processor by PragmatIC
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Online wraper

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Re: 8-bit uC - is there even a point?
« Reply #405 on: October 12, 2018, 10:44:11 am »
Are there any 3 cent 32 bit microcontrollers?   >:D

How about 1 cent, and flexible?

$0.01 Flexible Plastic ARM Processor by PragmatIC
Except it's not 1 cent, not a real product, only prototype and even ARM licence is more expensive than 1 cent. A few cents sometime in the future, maybe, just as a guy on the right said.
 

Online coppice

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Re: 8-bit uC - is there even a point?
« Reply #406 on: October 12, 2018, 10:47:41 am »
Are there any 3 cent 32 bit microcontrollers?   >:D

How about 1 cent, and flexible?

$0.01 Flexible Plastic ARM Processor by PragmatIC
Except it's not 1 cent, not a real product, only prototype and even ARM licence is more expensive than 1 cent. Sometime in the future, maybe, just a a guy on the right said.
They made an ARM1. That is licence free. To make a commercial product they have licence free options. like the RISC/V. People usually can't escape all royalties, because they will have to used some silicon IP, like a flash block. Since these people are not using any silicon technology, they will be creating 100% of their process related IP.
 

Online wraper

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Re: 8-bit uC - is there even a point?
« Reply #407 on: October 12, 2018, 11:03:07 am »
They made an ARM1. That is licence free. To make a commercial product they have licence free options. like the RISC/V. People usually can't escape all royalties, because they will have to used some silicon IP, like a flash block. Since these people are not using any silicon technology, they will be creating 100% of their process related IP.
It is cortex M0, not ARM1. In video was even said that it will become commercially viable when they will make a single chip few mm in size. Which means it's not commercially viable currently. And who would make a real product based on ARM1 to begin with?
EDIT: And anyway, it's not something you would use in a low and likely medium quantity product. It's a niche thing, flexible electronics. You won't solder this thing on the PCB.
« Last Edit: October 12, 2018, 11:18:22 am by wraper »
 

Offline technix

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Re: 8-bit uC - is there even a point?
« Reply #408 on: October 12, 2018, 01:10:39 pm »
They made an ARM1. That is licence free. To make a commercial product they have licence free options. like the RISC/V. People usually can't escape all royalties, because they will have to used some silicon IP, like a flash block. Since these people are not using any silicon technology, they will be creating 100% of their process related IP.
It is cortex M0, not ARM1. In video was even said that it will become commercially viable when they will make a single chip few mm in size. Which means it's not commercially viable currently. And who would make a real product based on ARM1 to begin with?
EDIT: And anyway, it's not something you would use in a low and likely medium quantity product. It's a niche thing, flexible electronics. You won't solder this thing on the PCB.
If it were ARM1 or ARM2 it could have been 1 cent: those cores have long past their patent expiry dates, and if you recreate the cores using a free implementation (e.g. the open source Amber core, which implements ARM2) there is nothing you need to pay other than fab. If you can squeeze the economy of scale up you get that price point.

Although if ou use RV32IMC it would have the same benefit.
 

Online wraper

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Re: 8-bit uC - is there even a point?
« Reply #409 on: October 12, 2018, 01:28:50 pm »
If it were ARM1 or ARM2 it could have been 1 cent: those cores have long past their patent expiry dates, and if you recreate the cores using a free implementation (e.g. the open source Amber core, which implements ARM2) there is nothing you need to pay other than fab. If you can squeeze the economy of scale up you get that price point.
And no one would buy them because they would suck, therefore not possible to make such amounts to achieve low cost.
 

Offline brucehoult

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Re: 8-bit uC - is there even a point?
« Reply #410 on: October 13, 2018, 08:55:42 am »
If it were ARM1 or ARM2 it could have been 1 cent: those cores have long past their patent expiry dates, and if you recreate the cores using a free implementation (e.g. the open source Amber core, which implements ARM2) there is nothing you need to pay other than fab. If you can squeeze the economy of scale up you get that price point.

ARM7TDMI was 1994. That should be out of protection now.

Quote
Although if ou use RV32IMC it would have the same benefit.

Just RV32IM for ARM2 equivalence. C gets you to competitive with Thumb2 on code size, and better and much cleaner than the mix of ARM32 and Thumb1 you need on ARM7TDMI.

Cortex M0(+) is of course almost exactly Thumb1 without any ARM mode and just a couple of extra instructions to handle system tasks.

I expect ARM2 code is a bit more compact than RV32IM -- they do get some benefit from predication, the free shifter on the 2nd argument, all those addressing modes, and LDM/STM. But RISC-V gets a decent size and speed benefit from the single-instruction "compare two registers and branch" instruction. And ARM needs to spill variables to RAM a lot more (and only passes 4 arguments in registers). I don't know if anyone has made a close comparison as ARM32 is basically obsolete and Thumb2 is what everyone uses. On RISC-V if you have more than maybe 1 KB of program code then it's a net benefit to implement the 16 bit instructions, so basically everyone does RV32IMC if not RV32IMAC (the Atomic instructions are trivial to implement if you only have one processor)
 

Offline technix

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Re: 8-bit uC - is there even a point?
« Reply #411 on: October 13, 2018, 09:25:14 am »
If it were ARM1 or ARM2 it could have been 1 cent: those cores have long past their patent expiry dates, and if you recreate the cores using a free implementation (e.g. the open source Amber core, which implements ARM2) there is nothing you need to pay other than fab. If you can squeeze the economy of scale up you get that price point.

ARM7TDMI was 1994. That should be out of protection now.
Then why is LPC2103 and AT91SAM7S128 still that damn expensive?

Speaking of, since Cortex-A72 can still run ARM7TDMI code almost as-is, how much of ARM7TDMI isn’t covered in newer patents?
 

Online GeorgeOfTheJungle

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Re: 8-bit uC - is there even a point?
« Reply #412 on: October 13, 2018, 09:45:10 am »
And no one would buy them because they would suck [...]

But never as much as that chinese 3 cents µC  >:D
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Offline brucehoult

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Re: 8-bit uC - is there even a point?
« Reply #413 on: October 13, 2018, 09:56:31 am »
ARM7TDMI was 1994. That should be out of protection now.
Then why is LPC2103 and AT91SAM7S128 still that damn expensive?

Interesting. $8 - $10.

Is there any good reason to use one of those rather than a Cortex M, other than "we already have a product and don't want to redesign it"?
 

Online GeorgeOfTheJungle

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Re: 8-bit uC - is there even a point?
« Reply #414 on: October 13, 2018, 01:16:41 pm »
I don't think I've ever seen as much loathing of a computer design as you get when you push a paged solution, or as much relief as you get when you tell people you're going to stretch the address registers to solve their memory constraints.

Yes, exactly, the Apple IIe's AUX mem was perhaps the best example of how not to do it. Even worse, you can never be completely sure what state it's in after a reset!
« Last Edit: October 13, 2018, 01:19:58 pm by GeorgeOfTheJungle »
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Offline mikeselectricstuff

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Re: 8-bit uC - is there even a point?
« Reply #415 on: October 13, 2018, 09:13:07 pm »
ARM7TDMI was 1994. That should be out of protection now.
Then why is LPC2103 and AT91SAM7S128 still that damn expensive?

Interesting. $8 - $10.

Is there any good reason to use one of those rather than a Cortex M, other than "we already have a product and don't want to redesign it"?
Exactly this. Also lower volumes.
Would you rather a part you use in production went obsolete an unobtainable  overnight, or just increased in price ?
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Online nctnico

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Re: 8-bit uC - is there even a point?
« Reply #416 on: October 14, 2018, 08:49:13 pm »
If it were ARM1 or ARM2 it could have been 1 cent: those cores have long past their patent expiry dates, and if you recreate the cores using a free implementation (e.g. the open source Amber core, which implements ARM2) there is nothing you need to pay other than fab. If you can squeeze the economy of scale up you get that price point.
ARM7TDMI was 1994. That should be out of protection now.
Then why is LPC2103 and AT91SAM7S128 still that damn expensive?
Probably because these are old MCUs and are now being milked to support legacy designs. They used to be a whole lot cheaper a decade ago.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online coppice

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Re: 8-bit uC - is there even a point?
« Reply #417 on: October 14, 2018, 08:57:13 pm »
If it were ARM1 or ARM2 it could have been 1 cent: those cores have long past their patent expiry dates, and if you recreate the cores using a free implementation (e.g. the open source Amber core, which implements ARM2) there is nothing you need to pay other than fab. If you can squeeze the economy of scale up you get that price point.
ARM7TDMI was 1994. That should be out of protection now.
Then why is LPC2103 and AT91SAM7S128 still that damn expensive?
Probably because these are old MCUs and are now being milked to support legacy designs. They used to be a whole lot cheaper a decade ago.
They are probably cheap now, if you are a serious user still running a production line.
 

Offline brucehoult

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Re: 8-bit uC - is there even a point?
« Reply #418 on: October 15, 2018, 12:02:48 am »
If it were ARM1 or ARM2 it could have been 1 cent: those cores have long past their patent expiry dates, and if you recreate the cores using a free implementation (e.g. the open source Amber core, which implements ARM2) there is nothing you need to pay other than fab. If you can squeeze the economy of scale up you get that price point.
ARM7TDMI was 1994. That should be out of protection now.
Then why is LPC2103 and AT91SAM7S128 still that damn expensive?
Probably because these are old MCUs and are now being milked to support legacy designs. They used to be a whole lot cheaper a decade ago.
They are probably cheap now, if you are a serious user still running a production line.

Serious users running production lines who only need ARM7TDMI performance (or even M3/M4) should probably be thinking about making their own SoC with as much as possible of the other chips they're using now integrated onto it.

I think you can now get a mask set for 180nm for $30k or so and even less for 350nm and then go into making a wafer worth of your custom SoC whenever you need for ... I'm not sure ... maybe $1 each.
 


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