Author Topic: 8-bit uC - is there even a point?  (Read 27458 times)

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Offline coppice

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Re: 8-bit uC - is there even a point?
« Reply #225 on: October 02, 2018, 01:31:41 pm »
Quote
PS. Also why TSSOP? They are harder to hand solder than DFN/QFN. The gull wing sucks and stores solder, so bridging happens all the time with short pad extension. With QFN, I can do 0.2mm extension per side and they still don't bridge.
At least one practical reason is that QFN are more culpable to cracked solder joints due to board flex and/or thermal expansion/cycling. The difference has been tested. And regarding deep thermal cycling, apparently gull wing chips can be more than an order of magnitude better in some of these tests.
The reliability of QFN mounting is quite variable. If people take the thermal stress issues seriously during soldering, as people normally do with BGA packages, results can be very good. if you fail to get things evenly heated during the soldering process you can get very poor results. So, don't expect most hand soldered QFNs to achieve wonderful reliability. The thermal expansion of the QFN package material has been chosen to be close to that of FR4. If you tried to use any other PCB material you might find reliability problems with QFNs.
 

Online Nauris

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Re: 8-bit uC - is there even a point?
« Reply #226 on: October 02, 2018, 06:32:07 pm »
I visited a TV manufacturing plant from Nokia in Germany in the early 90's and even back then they placed all through-hole components automatically. The machines would even detect a failure, pull the part back out (bin it) and re-insert a new one. I'd say those through hole placement machines where more impressive than those newfangled SMT p&p machines  8)
The SMT parts where glued to the solder side and the whole PCB would then go through the wave soldering machine.

Yes, they are truly impressive, like the Panasonic AV132 puts components in like good old chip-shooter places chips at 30000 per hour or thereabout. They just appear on the board faster than eye can see!


These days there is also very much interest and growing market in the odd-form flexible thru-hole placement machines capable of placing anything from axial resistor on tape&reel to loose connectors or big transformers.
Like the new one from Fuji:
http://smt.fuji.co.jp/e/datas/movie/smartfab/Insertion(2).mp4
Or the Cencorp (Chinese-owned company by the way):
 

Online wraper

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Re: 8-bit uC - is there even a point?
« Reply #227 on: October 02, 2018, 06:44:49 pm »
I visited a TV manufacturing plant from Nokia in Germany in the early 90's and even back then they placed all through-hole components automatically. The machines would even detect a failure, pull the part back out (bin it) and re-insert a new one. I'd say those through hole placement machines where more impressive than those newfangled SMT p&p machines  8)
The SMT parts where glued to the solder side and the whole PCB would then go through the wave soldering machine.

Yes, they are truly impressive, like the Panasonic AV132 puts components in like good old chip-shooter places chips at 30000 per hour or thereabout. They just appear on the board faster than eye can see!
It's nowhere near to fully automated TH component placement. All it places are axial parts with 2 leads like resistors.
 

Offline Bassman59

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Re: 8-bit uC - is there even a point?
« Reply #228 on: October 02, 2018, 07:02:28 pm »
Though I still see the center pad of QFN's a right pain to get right every time, you have to generally get weird with your paste masks to get better than 99.9% yields, which generally leads me to fitting a dot when its needed, vs a full pad,

The data sheets for QFN-with-pad parts recommend a pattern of small square holes in the paste mask for the pad instead of filling the whole pad. For example, Silicon Labs' Si5344 data sheet says to use a 3x3 array of 1.25 mm square cut-outs on 1.8 mm pitch. The pad itself is 5.2 mm square.
 

Online Nauris

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Re: 8-bit uC - is there even a point?
« Reply #229 on: October 02, 2018, 08:06:45 pm »

Yes, they are truly impressive, like the Panasonic AV132 puts components in like good old chip-shooter places chips at 30000 per hour or thereabout. They just appear on the board faster than eye can see!
It's nowhere near to fully automated TH component placement. All it places are axial parts with 2 leads like resistors.
It needs bit more explanation, it seems. Automated thru-hole line consist of three kinds of machines. Typically there is first the axial component inserting machine (ex. AV132), after that comes the radial inserting machine placing radial components, like small electrolytics, film caps and such. Then at last there is one or usually more odd-form machines placing rest of components, like connectors, transformers, big electrolytics and such. That kind of line you would be using, if you were making thru-hole only boards.

Of course that is rarely case today, you usually have also smd machines inline and often no axial or radial inserter, but only a few odd-form machines handling the thru-hole component placement.
« Last Edit: October 02, 2018, 08:09:35 pm by Nauris »
 

Offline westfw

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Re: 8-bit uC - is there even a point?
« Reply #230 on: October 02, 2018, 10:09:41 pm »
Quote
Clearly, it's ST's addition, and not the "ARM's option". The name is "CCM" for core-coupled memory instead of "TCM".
Thanks for the clarification and example part.
I guess my point was that claiming 32bit CPUs are "easier to use" than 8-bit chips is a bit ... misleading, if you're going to end up using a relatively complex-to-use vendor-specific feature to get the job done.  On the other hand, writing timing-critical "needs every cycle" code for an 8bit chip isn't an easy task, either.  Just ... different.
 

Offline PCB.Wiz

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Re: 8-bit uC - is there even a point?
« Reply #231 on: October 03, 2018, 04:23:02 am »
Really, entire world? Then why new parts still appear no the market?

Quote
Semiconductor MCU revenue market forecast –millions of dollars

Nice stats, which show that the 4 & 16 bitters are the ones that stagnate, but the 8b & 32b are growing at actually very similar CAGR
 

Offline PCB.Wiz

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Re: 8-bit uC - is there even a point?
« Reply #232 on: October 03, 2018, 04:33:48 am »
IIRC, according to Hackaday, that's not the case anymore.

https://hackaday.com/2018/04/15/rip-dip-arm/

Interesting, and no real surprise.
That was a marketing departments idea of 'attention getting' and not a practical solution for almost anything.
Even in the engine room of the 8b MCU world, 8 pin controllers are fading, with a new QFN20 being often smaller and cheaper than last year's So8...
 

Online nctnico

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Re: 8-bit uC - is there even a point?
« Reply #233 on: October 03, 2018, 06:02:02 am »
Really, entire world? Then why new parts still appear no the market?

Quote
Semiconductor MCU revenue market forecast –millions of dollars

Nice stats, which show that the 4 & 16 bitters are the ones that stagnate, but the 8b & 32b are growing at actually very similar CAGR
These kind of stats say nothing about the number of designs which is a way more interesting number. 8 bit makes sense in very high volume if cost is an issue so just looking at dollar figures gives a very incomplete picture. You can't really see where the market is going from it.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline GeorgeOfTheJungle

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Re: 8-bit uC - is there even a point?
« Reply #234 on: October 03, 2018, 07:25:01 am »
4.5x times the clock speed == 9.4x times faster:

« Last Edit: October 03, 2018, 10:08:42 am by GeorgeOfTheJungle »
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Offline Siwastaja

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Re: 8-bit uC - is there even a point?
« Reply #235 on: October 03, 2018, 07:55:14 am »
I guess my point was that claiming 32bit CPUs are "easier to use" than 8-bit chips is a bit ... misleading

Thanks! I think no one disagrees here; I haven't seen anyone claiming this, so it makes little sense to go against such a strawman any longer.

Of course the super simple 8-bitter is going to be easier to use and understand. It's so much smaller and less complex that it has to be easier.

But by how much? And what's the end result?

If you compare a $3 AVR to a $3 STM32, you'll see the latter has about:
10x larger number of peripherals, each of which has...
about 10x more features, hence complexity; and
then, the core/bus system/memory system as a whole performs about 20-100x faster for computational tasks.

You can use it to do a completely different league of things.

It's inevitable this is going to be hundreds of times more complex, internally. If the pricing was linear wrt some kind of "capability" index, the cost for the $3 STM32 would be $300. Or the cost for the $3 AVR should be $0.03.

So, people are likely to expect this $3 STM32 to be hundreds of times more difficult to use.

Now, coupled to the fact that people see cryptic code examples where blinking an LED and reading the ADC takes 500 lines of code (autogenerated or copypasted), while the same on AVR takes 15 lines, this reinforces the assumption. The problem is, it really takes about the same 15 lines of code to do the same on the said STM32, if done sanely! Actually, everything is surprisingly similar, there just are more features, which can be mostly ignored when not needed, but they give you a slight bit of extra mental overhead anyway.

Now, my point is, a modern typical ARM MCU hides the extra complexity fairly well, behind a sane structure. Some very vendor-specific and odd requirements from the 8-bit world simply disappear, and work out straight out of the box. Having everything clearly memory mapped without strange address space limitations and workaround is a prime example. This sane architecture offsets for the extra complexity elsewhere. The end result is surprisingly easy to grasp.

Of course, if you have done a lot of work on 8-bitters, you may be expecting the same "rules" of complexity are true on a 32-bit ARM, as well. For example, you seem to be expecting that the Core-coupled memory of STM32F334 is...

Quote
you're going to end up using a relatively complex-to-use vendor-specific feature to get the job done.

I can see where you are coming from with this assumption; if there was such an extra memory section on a PIC, it would (very likely) be relatively complex-to-use and at least very vendor-specific. But you are wrong. Said CCM is utterly trivial. Actually, it just works out of the box. It doesn't even need a single enable bit. No configuration. No custom tools, no knowledge of anything vendor specific. The memory address range is given in the manual and it just works there. Put your code to this address range, and it runs fast. Took literally less than 5 minutes for me to do this first time ever, worked on the first compilation. Completely agnostic to the workflow, libraries or compiler.

Of course, if you have never looked at how to use C and/or linker to define in which memory section your code and/or variables go to (or similar in the graphical settings of your IDE of choice), you need to learn that, but it just couldn't be easier, and definitely no vendor-specific anything. I use a custom linker script and my own startup code since it seems most flexible to me and I surely know what I get, but I guess there are easier point/click ways.

On AVR, for example, you can only run instructions from flash, and reading (const) data out of the flash requires specific instructions, and AFAIK no compiler can generate this code automatically; you use specific functions/macros to read access flash:
https://www.nongnu.org/avr-libc/user-manual/group__avr__pgmspace.html
Concepts like this just don't exist on ARM. Complex things are of course difficult, but simple things tend to be simple, which isn't always the case on the 8-bit world!
« Last Edit: October 03, 2018, 07:58:46 am by Siwastaja »
 
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Online wraper

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Re: 8-bit uC - is there even a point?
« Reply #236 on: October 03, 2018, 08:30:23 am »
These kind of stats say nothing about the number of designs which is a way more interesting number. 8 bit makes sense in very high volume if cost is an issue so just looking at dollar figures gives a very incomplete picture. You can't really see where the market is going from it.
You can at least assume that 8 bitters are sold/used in significantly higher numbers. Because amount shown is in money and 8 bitters are cheaper, especially super cheap end which go into mass produced devices.
« Last Edit: October 03, 2018, 09:38:02 am by wraper »
 

Online nctnico

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Re: 8-bit uC - is there even a point?
« Reply #237 on: October 03, 2018, 09:06:40 am »
Quote
Clearly, it's ST's addition, and not the "ARM's option". The name is "CCM" for core-coupled memory instead of "TCM".
Thanks for the clarification and example part.
I guess my point was that claiming 32bit CPUs are "easier to use" than 8-bit chips is a bit ... misleading,
The other way around: claiming that 8bit CPUs are easier to use is equally misleading. The peripherals in a microcontroller are a different story and you can find examples of complicated peripherals regardless the number of bits in the CPU.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline MT

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Re: 8-bit uC - is there even a point?
« Reply #238 on: October 03, 2018, 11:25:07 am »
What is the thing with DIP?
Mount DIP on one side and SMT between the legs on the other side! Chop the legs of a DIP to turn it into a SMT. Aviation and Space?
 

Offline mikeselectricstuff

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Re: 8-bit uC - is there even a point?
« Reply #239 on: October 03, 2018, 12:22:59 pm »
The other way around: claiming that 8bit CPUs are easier to use is equally misleading. The peripherals in a microcontroller are a different story and you can find examples of complicated peripherals regardless the number of bits in the CPU.
For a simple job, most 8-bits are easier than most larger MCUs, however once you get stuck into real work, the additional processing power, ROM/RAM space and peripheral functionality can make some jobs much easier on bigger parts, as there's less need to optimise/work around the limitations of 8-bit devices
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Offline snarkysparky

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Re: 8-bit uC - is there even a point?
« Reply #240 on: October 03, 2018, 07:24:18 pm »
PIC24 series is every bit as easy to use as 8 bit but you get vastly better chip.

I don't understand the lack of love for that series.
 

Offline rx8pilot

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Re: 8-bit uC - is there even a point?
« Reply #241 on: October 03, 2018, 07:46:44 pm »
PIC24 series is every bit as easy to use as 8 bit but you get vastly better chip.

I don't understand the lack of love for that series.

I somewhat arbitrarily chose Atmel a number of years ago. It was partly based on the size and depth of information available on the internet at the time. After getting setup and dialed in for most of the basic functions I needed - I had no real interest in learning another product family - even if it was 'better'

Now, I am at a place where I am ready for more power, better peripherals, better everything. I have emotionally prepared myself for a learning curve to get that.
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Offline mikeselectricstuff

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Re: 8-bit uC - is there even a point?
« Reply #242 on: October 03, 2018, 08:14:58 pm »
PIC24 series is every bit as easy to use as 8 bit but you get vastly better chip.

I don't understand the lack of love for that series.
It has some nice features, especially the very flexible peripheral pin mapping, good at low power, but 3.3v only ( apart from one or two), and can be more expensive than some of the PIC32 range.
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Online NorthGuy

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Re: 8-bit uC - is there even a point?
« Reply #243 on: October 03, 2018, 08:20:27 pm »
For a simple job, most 8-bits are easier than most larger MCUs, however once you get stuck into real work, the additional processing power, ROM/RAM space and peripheral functionality can make some jobs much easier on bigger parts, as there's less need to optimise/work around the limitations of 8-bit devices

I think for simple job, they're all the same. Of course, there are some peculiarities, but, in general, the process is the same. You write a code in C. There's some basic initialization done by CRT, and then you start from there. You can debug, possibly simulate. Since the job is simple, you don't really worry about the resources - you get the biggest chip in your particular series (meaning everything is the same but lots of memory etc.) and use it for prototyping. Then you watch the resources and scale your chip down for the final board. Since it's the same process, you get similar development time.  Nothing is dramatically different no matter what chip you chose, unless you select something really stupid and unsuitable.

If you have demands for something particular, things change. Say, you want to simultaneously sample 8 ADC channels. So, you get a chip with ADC module which can cycle through your channels fast enough. Or, you need to communicate with something at 50 MHz SPI, so you select a chip which can do 50 MHz SPI. Or, you need 50 MTap/s FIR, so you select a DSP chip which can do this. Or, you need to do lots of fast floating point calculations (such as inverting matrices etc.), so you select an ARM chip with hardware floating point support. There's no other way. If you select an unsuitable chip it won't work, or will make your job much more complex that it needs to be.

However, if you don't have any particular needs, but select a big chip so that you could bloat more, or if you select an ARM chip because of the marketing buzz on the Internet, there's no merit in such decisions. Unfortunately, much too often that's how the decisions are made.

 

Online NorthGuy

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Re: 8-bit uC - is there even a point?
« Reply #244 on: October 03, 2018, 08:25:46 pm »
PIC24 series is every bit as easy to use as 8 bit but you get vastly better chip.

I don't understand the lack of love for that series.

I like them too. I don't understand the low popularity.

Although Microchip screwed up with PIC24 memory big time, so if you want above 32K of RAM, things get very messy. Which certainly limits the growth. Microchip are good at screwing up with memory. They managed to fragment even PIC32MZ.
 

Online langwadt

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Re: 8-bit uC - is there even a point?
« Reply #245 on: October 03, 2018, 08:40:21 pm »
PIC24 series is every bit as easy to use as 8 bit but you get vastly better chip.

I don't understand the lack of love for that series.

I somewhat arbitrarily chose Atmel a number of years ago. It was partly based on the size and depth of information available on the internet at the time. After getting setup and dialed in for most of the basic functions I needed - I had no real interest in learning another product family - even if it was 'better'

Now, I am at a place where I am ready for more power, better peripherals, better everything. I have emotionally prepared myself for a learning curve to get that.

and if you are going to upgrade and have a learning curve why go half way and pick 16bit from a single source when
you can go all the way to 32 bit and have numerous similar choices from many sources

 

Offline coppice

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Re: 8-bit uC - is there even a point?
« Reply #246 on: October 03, 2018, 08:44:17 pm »
PIC24 series is every bit as easy to use as 8 bit but you get vastly better chip.

I don't understand the lack of love for that series.

I somewhat arbitrarily chose Atmel a number of years ago. It was partly based on the size and depth of information available on the internet at the time. After getting setup and dialed in for most of the basic functions I needed - I had no real interest in learning another product family - even if it was 'better'

Now, I am at a place where I am ready for more power, better peripherals, better everything. I have emotionally prepared myself for a learning curve to get that.

and if you are going to upgrade and have a learning curve why go half way and pick 16bit from a single source when
you can go all the way to 32 bit and have numerous similar choices from many sources
This currently a strong view amongst engineering managers, and it makes no sense. Nobody has to learn much about a new core, whether its 16 or 32 bits. They program in C, and only need to know a few simple things about the actual core. Its the peripherals that provide all the power, and take all the effort to learn. There is almost no commonality of peripherals from one silicon vendor to the next.
 
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Online nctnico

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Re: 8-bit uC - is there even a point?
« Reply #247 on: October 03, 2018, 08:54:25 pm »
I agree. You need to know very little about the CPU core itself. Just that it is 32 bit so you can use 32 bit numbers without a performance penalty. The biggest variation are the peripherals and these can make or break the efficiency of working with a particular microcontroller. My advice would be to really dig into datasheets, user manuals and errata sheets of at least half a dozen microcontroller from various vendors before making a final choice. It is what I did when I moved to ARM microcontrollers. Heck I even made some projects to see which one worked well in a real world situation (bringing the board up, debugging, programming tools, stability, etc). Choosing something which seems popular isn't a good idea because many people look at part cost only and not at engineering time.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline mikeselectricstuff

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Re: 8-bit uC - is there even a point?
« Reply #248 on: October 03, 2018, 08:55:29 pm »
There is almost no commonality of peripherals from one silicon vendor to the next.
CMSIS?
I'll get my coat.... :-DD :-DD
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Offline coppice

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Re: 8-bit uC - is there even a point?
« Reply #249 on: October 03, 2018, 10:58:55 pm »
There is almost no commonality of peripherals from one silicon vendor to the next.
CMSIS?
I'll get my coat.... :-DD :-DD
Its a good joke, but it doesn't seem like people fall for it very often. Once you get past the "we use standard ARM cores" step, and the engineering manager is happy to listen to you extol the virtues of all the unique stuff in your peripherals they know the score. They know this will require their engineers take some serious time to be fully conversant with your peripheral set. They know CMSIS will only cut it for very basic uses, loosing access to all the clever stuff in your peripherals. They know whatever clever stuff they implement with your MCU will be completely non-portable. They still insist on that ARM core, though.
 


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