5 ms·

I'm not a hardware knowledgable guy, but would love to read/hear an intro about what chip design is all about (at a lay person's level I guess). I understand t

I'm not a hardware knowledgable guy, but would love to read/hear an intro about what chip design is all about (at a lay person's level I guess). I understand that ARM sells core designs, and that each company assembles them / designs them in the way suits their performance needs, and then gets them manufactured? But what does that really mean? What is the "user" doing? Are they arranging them like kids' Lego blocks on a die surface? Dragging and dropping blocks of code? Are they tweaking the voltage settings? Are they combining them in ways that do sequential operations special to them? What's the added step here? Like, why doesn't ARM just create the chips that the end OEMs want? Is it like cooking or chemistry? What's the closest analogy? I would love to get a more intuitive feel about what chip design is all about. Thanks!

silman 8y ago
ARM designs processors, but just the processor. I̶t̶ ̶d̶o̶e̶s̶n̶'̶t̶ ̶a̶d̶d̶ ̶p̶e̶r̶i̶p̶h̶e̶r̶a̶l̶s̶ ̶t̶o̶ ̶i̶t̶;̶ (also wrong here, apparently they make plenty of peripherals)., that's the job of the vendor who uses the processor and integrates it with RAM, Flash, protocol hardware (SPI, I2C, Serial, USB, etc), Timers, and all the other goodies that make a microcontroller easier to use because you dont need fifteen other chips to get it doing what you want it to do.Imagine needing to buy a separate chip so you can speak I2C, another to speak SPI, another to have a counter running and interrupt the processor every X seconds, another to store program memory, another to convert analog signal to digital; it would be unwieldly, so these vendors take the processor and attach these peripherals and say "the processor can use this peripheral by writing 0xAB to its register located at 0x12345678. So you can think of ARM as designing the engine, and the vendors as taking the engine design then adding the rest of the cars features (chassis, electronics, navigation, etc) around it, then building and selling it. "Why don't the vendors just design their own processor to go with their own peripherals?" you might ask. Well designing a processor is MUCH harder to do well than any of the individual peripherals. There is a lot more going on with a processor and it's at least an order of magnitude more complex than any of the peripherals that go with it. But that doesn't mean it's not done; Atmel designed the AVR architecture and this is the processor architecture that dominates the Arduino world. Atmel sells microcontrollers with their AVR architecture processor and their own peripheral designs as well. But AVR is mostly 8-bit and they can't compete with the performance of ARMs 32-bit designs; which is why you see ARM is most embedded applications. The design for the processor is made in a program that lets you "lay out" the hardware at the transistor level and specify processes for it (like a lithographic mask) but ARM never carries out these processes, these must be taken care of by a fabrication facility. Oftentimes these vendors don't even have fabs themselves, they just design the rest of the "car" and then have it fab'ed by a third party. ~A̶R̶M̶ ̶d̶o̶e̶s̶n̶'̶t̶ ̶w̶a̶n̶t̶ ̶t̶o̶ ̶d̶e̶s̶i̶g̶n̶ ̶p̶e̶r̶i̶p̶h̶e̶r̶a̶l̶s̶ ̶a̶n̶d̶ ̶f̶a̶b̶r̶i̶c̶a̶t̶e̶ ̶c̶h̶i̶p̶s̶ ̶(̶i̶t̶ ̶d̶o̶e̶s̶n̶'̶t̶ ̶e̶v̶e̶n̶ ̶h̶a̶v̶e̶ ̶a̶ ̶f̶a̶b̶,̶ ̶n̶o̶r̶ ̶d̶o̶e̶s̶ ̶i̶t̶ ̶w̶a̶n̶t̶ ̶t̶o̶ ̶d̶e̶a̶l̶ ̶w̶i̶t̶h̶ ̶3̶r̶d̶ ̶p̶a̶r̶t̶y̶ ̶f̶a̶b̶s̶)̶.̶~ (Looks like i'm totally wrong here, also why doesn't HN have strikethrough comments implemented?). They do what they do - design processors - and they do it really well, so well in fact that vendors are more than willing to pay for a license to use their processors in their own chips so that the vendor doesn't have to deal with the headache of making a really good processor.
- monocasa 8y ago
  ARM designs plenty of peripherals. Nearly all ARM SoCs use a PL011 UART, quite a bit have SMMUs, the Mali GPU is an ARM design, etc. And they work very very closely with fabs; you can't really design highish performance cores like their's without working with the fabs. You'd have all sorts of weird bottlenecks, and wouldn't hit a competitive frequency (think under 100Mhz if you didn't take into account fab design rules). What they don't do is sell predesigned SoCs (outside of dev systems). They give you all of the tools you need to integrate your own SoC so that you can take nearly all of the capital risk.
  - silman 8y ago
    Huh i guess i made a bad assumption. Though i'm not surprised they make peripherals and work with the fabs, i just assumed it stayed away from it as much as it could. edited my comment, thanks for the info!
fpgaminer 8y ago
You've got the right general idea already :) > I understand that ARM sells core designs, and that each company assembles them / designs them in the way suits their performance needs, and then gets them manufactured? Most consumers of ARM cores are simply interested in integrating them into a larger design; usually an SoC. Not so much in tweaking performance, though certainly they'll choose whether to prioritize performance or power in their application. > But what does that really mean? What is the "user" doing? Are they arranging them like kids' Lego blocks on a die surface? Dragging and dropping blocks of code? Pretty much like Lego blocks. Most shops just want an SoC that does X, Y, and Z with Foo requirements. So they grab an ARM core, an HDMI 2.0 RX core, and H.265 core, and glue them together. Depending on what tools they're using this "gluing" is specified in different ways. You can design it somewhat abstract in a block diagram, where you specify all the cores you want, specify what (virtual) pins from each core connect to what others, and maybe tweak a few parameters on some of the cores. It looks kinda like this: https://www.altera.com/content/dam/altera-www/global/en_US/images/support/examples/quartus/images/altpll_fig2.gif https://www.altera.com/content/dam/altera-www/global/en_US/i... Or there are even higher level tools that let you specify and hook these things together in a GUI specifically designed for building designs like this. They look like this: https://i.stack.imgur.com/yud23.png https://i.stack.imgur.com/yud23.png But those and other higher level tools all basically just have a compiler that converts specifications into code (Verilog or VHDL). That is then handed to another compiler which creates a netlist. Think of this like assembly code but for hardware. It specifies the whole design at the level of logical operations. 2-bit AND here, 4-bit Full Adder there, etc. Finally that netlist is thrown through _another_ compiler which does final place and route. Place and route is where the netlist is converted into the transistors and wires for the actual die, and then rendered out into all the layer masks that will be sent to the fab. (I'm glossing over a few details here. E.g. place and route is actually working from a library of transistor designs for each possible logical gate, pre-designed by the silicon fab that your going to send your masks to.). It sounds simple, but until place and route your design is just an abstract spaghetti of logical operations and connections between. Place and route has to solve an NP-Complete optimization to figure out where, on the physical die, all the transistors are going to go, given a set of constraints (transistors need to be close enough to their neighbors to achieve the performance requirements). Anyway, stepping back, the design phase is where you specify various parameters for the cores. These parameters typically change things like enabling/disabling features of the core. For example on an ARM core you might disable the math co-processor to save space/power if you don't need it; make the pipelines smaller, etc. These are configuration options; you aren't editing the ARM core's code. The core itself specifies how its code changes depending on configuration options. The place and router phase is where you have some control over power/performance. You can tell the tools to focus on power if your design needs to be low power. It'll then design the transistors in such a way that it'll use less power but also lose some performance. Or the opposite. Of course how the cores themselves are designed is important to power versus performance, and ARM cores probably have some configuration options that affect their behavior in that regard. And then the silicon you target is of the utmost importance for design trade offs. Targeting 7nm fabs versus something larger will usually mean a more power efficient and performant design, but will have _much_ higher up-front costs (the physical masks you deliver to the fab cost tens of millions of dollars or more). To be clear, this is the level at which _most_ consumers of ARM cores are working at. They're just putting Lego blocks together. The ARM core is just a black box in that regard. ARM delivers the core's "code" to you as a pre-processed netlist. You can't see its real code (you just see a chaotic spaghetti of logical operations). But some companies have more special needs and want to tweak the core in specific ways (e.g. Apple). They'll have special deals with ARM that give them access to the core's source code where they can make custom tweaks. But this is rare. Some companies have their own IP which they might integrate into a design. Their own cores, coded from scratch. These are coded in Verilog or VHDL, for the most part. > Like, why doesn't ARM just create the chips that the end OEMs want? ARM cores get used in TONS of custom silicon. Wifi routers, drones, cell phone chips, cell phone coprocessor chips, etc. So part of it is that ARM just couldn't possibly design and build all these different kinds of chips. It's also that ARM does what ARM does best: design ARM cores. That's a job that takes an entire company all to itself to accomplish. Anything else is just beyond the scope of their company (for now).

silman 8y ago

ARM designs processors, but just the processor. I̶t̶ ̶d̶o̶e̶s̶n̶'̶t̶ ̶a̶d̶d̶ ̶p̶e̶r̶i̶p̶h̶e̶r̶a̶l̶s̶ ̶t̶o̶ ̶i̶t̶;̶ (also wrong here, apparently they make plenty of peripherals)., that's the job of the vendor who uses the processor and integrates it with RAM, Flash, protocol hardware (SPI, I2C, Serial, USB, etc), Timers, and all the other goodies that make a microcontroller easier to use because you dont need fifteen other chips to get it doing what you want it to do.Imagine needing to buy a separate chip so you can speak I2C, another to speak SPI, another to have a counter running and interrupt the processor every X seconds, another to store program memory, another to convert analog signal to digital; it would be unwieldly, so these vendors take the processor and attach these peripherals and say "the processor can use this peripheral by writing 0xAB to its register located at 0x12345678. So you can think of ARM as designing the engine, and the vendors as taking the engine design then adding the rest of the cars features (chassis, electronics, navigation, etc) around it, then building and selling it. "Why don't the vendors just design their own processor to go with their own peripherals?" you might ask. Well designing a processor is MUCH harder to do well than any of the individual peripherals. There is a lot more going on with a processor and it's at least an order of magnitude more complex than any of the peripherals that go with it. But that doesn't mean it's not done; Atmel designed the AVR architecture and this is the processor architecture that dominates the Arduino world. Atmel sells microcontrollers with their AVR architecture processor and their own peripheral designs as well. But AVR is mostly 8-bit and they can't compete with the performance of ARMs 32-bit designs; which is why you see ARM is most embedded applications. The design for the processor is made in a program that lets you "lay out" the hardware at the transistor level and specify processes for it (like a lithographic mask) but ARM never carries out these processes, these must be taken care of by a fabrication facility. Oftentimes these vendors don't even have fabs themselves, they just design the rest of the "car" and then have it fab'ed by a third party. ~A̶R̶M̶ ̶d̶o̶e̶s̶n̶'̶t̶ ̶w̶a̶n̶t̶ ̶t̶o̶ ̶d̶e̶s̶i̶g̶n̶ ̶p̶e̶r̶i̶p̶h̶e̶r̶a̶l̶s̶ ̶a̶n̶d̶ ̶f̶a̶b̶r̶i̶c̶a̶t̶e̶ ̶c̶h̶i̶p̶s̶ ̶(̶i̶t̶ ̶d̶o̶e̶s̶n̶'̶t̶ ̶e̶v̶e̶n̶ ̶h̶a̶v̶e̶ ̶a̶ ̶f̶a̶b̶,̶ ̶n̶o̶r̶ ̶d̶o̶e̶s̶ ̶i̶t̶ ̶w̶a̶n̶t̶ ̶t̶o̶ ̶d̶e̶a̶l̶ ̶w̶i̶t̶h̶ ̶3̶r̶d̶ ̶p̶a̶r̶t̶y̶ ̶f̶a̶b̶s̶)̶.̶~ (Looks like i'm totally wrong here, also why doesn't HN have strikethrough comments implemented?). They do what they do - design processors - and they do it really well, so well in fact that vendors are more than willing to pay for a license to use their processors in their own chips so that the vendor doesn't have to deal with the headache of making a really good processor.

monocasa 8y ago
ARM designs plenty of peripherals. Nearly all ARM SoCs use a PL011 UART, quite a bit have SMMUs, the Mali GPU is an ARM design, etc. And they work very very closely with fabs; you can't really design highish performance cores like their's without working with the fabs. You'd have all sorts of weird bottlenecks, and wouldn't hit a competitive frequency (think under 100Mhz if you didn't take into account fab design rules). What they don't do is sell predesigned SoCs (outside of dev systems). They give you all of the tools you need to integrate your own SoC so that you can take nearly all of the capital risk.
- silman 8y ago
  Huh i guess i made a bad assumption. Though i'm not surprised they make peripherals and work with the fabs, i just assumed it stayed away from it as much as it could. edited my comment, thanks for the info!

fpgaminer 8y ago

You've got the right general idea already :) > I understand that ARM sells core designs, and that each company assembles them / designs them in the way suits their performance needs, and then gets them manufactured? Most consumers of ARM cores are simply interested in integrating them into a larger design; usually an SoC. Not so much in tweaking performance, though certainly they'll choose whether to prioritize performance or power in their application. > But what does that really mean? What is the "user" doing? Are they arranging them like kids' Lego blocks on a die surface? Dragging and dropping blocks of code? Pretty much like Lego blocks. Most shops just want an SoC that does X, Y, and Z with Foo requirements. So they grab an ARM core, an HDMI 2.0 RX core, and H.265 core, and glue them together. Depending on what tools they're using this "gluing" is specified in different ways. You can design it somewhat abstract in a block diagram, where you specify all the cores you want, specify what (virtual) pins from each core connect to what others, and maybe tweak a few parameters on some of the cores. It looks kinda like this: https://www.altera.com/content/dam/altera-www/global/en_US/images/support/examples/quartus/images/altpll_fig2.gif https://www.altera.com/content/dam/altera-www/global/en_US/i... Or there are even higher level tools that let you specify and hook these things together in a GUI specifically designed for building designs like this. They look like this: https://i.stack.imgur.com/yud23.png https://i.stack.imgur.com/yud23.png But those and other higher level tools all basically just have a compiler that converts specifications into code (Verilog or VHDL). That is then handed to another compiler which creates a netlist. Think of this like assembly code but for hardware. It specifies the whole design at the level of logical operations. 2-bit AND here, 4-bit Full Adder there, etc. Finally that netlist is thrown through _another_ compiler which does final place and route. Place and route is where the netlist is converted into the transistors and wires for the actual die, and then rendered out into all the layer masks that will be sent to the fab. (I'm glossing over a few details here. E.g. place and route is actually working from a library of transistor designs for each possible logical gate, pre-designed by the silicon fab that your going to send your masks to.). It sounds simple, but until place and route your design is just an abstract spaghetti of logical operations and connections between. Place and route has to solve an NP-Complete optimization to figure out where, on the physical die, all the transistors are going to go, given a set of constraints (transistors need to be close enough to their neighbors to achieve the performance requirements). Anyway, stepping back, the design phase is where you specify various parameters for the cores. These parameters typically change things like enabling/disabling features of the core. For example on an ARM core you might disable the math co-processor to save space/power if you don't need it; make the pipelines smaller, etc. These are configuration options; you aren't editing the ARM core's code. The core itself specifies how its code changes depending on configuration options. The place and router phase is where you have some control over power/performance. You can tell the tools to focus on power if your design needs to be low power. It'll then design the transistors in such a way that it'll use less power but also lose some performance. Or the opposite. Of course how the cores themselves are designed is important to power versus performance, and ARM cores probably have some configuration options that affect their behavior in that regard. And then the silicon you target is of the utmost importance for design trade offs. Targeting 7nm fabs versus something larger will usually mean a more power efficient and performant design, but will have _much_ higher up-front costs (the physical masks you deliver to the fab cost tens of millions of dollars or more). To be clear, this is the level at which _most_ consumers of ARM cores are working at. They're just putting Lego blocks together. The ARM core is just a black box in that regard. ARM delivers the core's "code" to you as a pre-processed netlist. You can't see its real code (you just see a chaotic spaghetti of logical operations). But some companies have more special needs and want to tweak the core in specific ways (e.g. Apple). They'll have special deals with ARM that give them access to the core's source code where they can make custom tweaks. But this is rare. Some companies have their own IP which they might integrate into a design. Their own cores, coded from scratch. These are coded in Verilog or VHDL, for the most part. > Like, why doesn't ARM just create the chips that the end OEMs want? ARM cores get used in TONS of custom silicon. Wifi routers, drones, cell phone chips, cell phone coprocessor chips, etc. So part of it is that ARM just couldn't possibly design and build all these different kinds of chips. It's also that ARM does what ARM does best: design ARM cores. That's a job that takes an entire company all to itself to accomplish. Anything else is just beyond the scope of their company (for now).