Post by thread:[PIC] software flow

Are there any good books or resources that you would recommend about designing software on the PIC? I don't mean "this is how you make an LED blink" or "this is how you drive a stepper motor" but more like a system-level design where you might have a timer-interrupt drive a state machine that would accomplish 10 different tasks that you have to do? (just an example, I don't know if that's how you'd actually do it) Also I've had a quick look at the likes of FreeRTOS - but I'm using assembly. I feel like the only benefit of using C would be that my code is more organized and perhaps quicker to develop (but then there'd be low level bugs I can't see easily) Does anyone use an RTOS with assembly in their PIC 18F project? Would it be very difficult to write some time-sharing code for a PIC? - Martin

On Tue, 22 Apr 2008, Martin wrote: {Quote hidden}> Are there any good books or resources that you would recommend about > designing software on the PIC? I don't mean "this is how you make an LED > blink" or "this is how you drive a stepper motor" but more like a > system-level design where you might have a timer-interrupt drive a state > machine that would accomplish 10 different tasks that you have to do? > (just an example, I don't know if that's how you'd actually do it) > > Also I've had a quick look at the likes of FreeRTOS - but I'm using > assembly. I feel like the only benefit of using C would be that my code > is more organized and perhaps quicker to develop (but then there'd be > low level bugs I can't see easily) > > Does anyone use an RTOS with assembly in their PIC 18F project? Would it > be very difficult to write some time-sharing code for a PIC? If you build your system as a pure state machine (lots or states and events and NO hanging around in a state waiting for something to happen) then multitasking can become VERY simplified. You could even run multiple state machines on the same CPU and have each one looking after a different task (they could send each other events or communicate in other simple ways). C is not very good for multi-tasking because C does not know about multi-tasking, instead you need to use a library which introduces overheads and the seperate tasks can interfere with each other and there is no way for the compiler to know or generate task safe code. Converting a straight forward C or ASM program into a state machine can easily become tedious and error prone since the better you break down the program into a state machine the more states and events you produce. The more states and events you have the harder it is to keep track of everything (maintain and debug it). So what you need a tool that is to state machines as a C compiler is to machine code. You need a tool that takes a high level description of a state machine (which is easy to maintain and debug) and from it generates executable machine code. From choise you would use a tool that uses state diagrams to describe the state machine and allows you to debug your code using the same state diagrams - kind of like source level debugging in C or BASIC but on the diagram. I have a tool like this and it is called ZMech. There are other tools around. Some require that you specify the state machine in a high level text based language. Others that allow you to use diagrams. Some will only generate complex C++. Others that will generate C. But I haven't come across any (other than ZMech) that will allow you to produce machine executable code and interactively debug it directly against the state diagrams. Going back to the alternate multi-tasking approach, there is the XCSB compiler which produces highly efficient machine code executables. The language has multi-tasking built into it and the compiler generates task safe function calls without resorting to the runtime overhead of a dynamic stack and multi-tasking library. The LITE edition of XCSB if free for hobbyist / student use (non-commercial) and you can get it from: http://www.xcprod.com/titan/XCSB The following might give you some ideas that you can either implement yourself (maybe with paper and pencil) or things to look out for in an automated dev tool: http://www.xcprod.com/titan/ZMECH-DOC/generate/state-machine/block-indx.html Regards Sergio Masci

I use a formal flowcharting tool, like Visio, but there are inexpensive ones that I like better. Flowcharting allows several people to work on a large project separately. --Bob Axtell sergio masci wrote: {Quote hidden}> On Tue, 22 Apr 2008, Martin wrote: > > >> Are there any good books or resources that you would recommend about >> designing software on the PIC? I don't mean "this is how you make an LED >> blink" or "this is how you drive a stepper motor" but more like a >> system-level design where you might have a timer-interrupt drive a state >> machine that would accomplish 10 different tasks that you have to do? >> (just an example, I don't know if that's how you'd actually do it) >> >> Also I've had a quick look at the likes of FreeRTOS - but I'm using >> assembly. I feel like the only benefit of using C would be that my code >> is more organized and perhaps quicker to develop (but then there'd be >> low level bugs I can't see easily) >> >> Does anyone use an RTOS with assembly in their PIC 18F project? Would it >> be very difficult to write some time-sharing code for a PIC? >> > > If you build your system as a pure state machine (lots or states and > events and NO hanging around in a state waiting for something to happen) > then multitasking can become VERY simplified. You could even run multiple > state machines on the same CPU and have each one looking after a different > task (they could send each other events or communicate in other simple > ways). > > C is not very good for multi-tasking because C does not know about > multi-tasking, instead you need to use a library which introduces > overheads and the seperate tasks can interfere with each other and there > is no way for the compiler to know or generate task safe code. > > Converting a straight forward C or ASM program into a state machine can > easily become tedious and error prone since the better you break down the > program into a state machine the more states and events you produce. The > more states and events you have the harder it is to keep track of > everything (maintain and debug it). > > So what you need a tool that is to state machines as a C compiler is to > machine code. You need a tool that takes a high level description of a > state machine (which is easy to maintain and debug) and from it generates > executable machine code. From choise you would use a tool that uses state > diagrams to describe the state machine and allows you to debug your code > using the same state diagrams - kind of like source level debugging in C > or BASIC but on the diagram. I have a tool like this and it is called > ZMech. There are other tools around. Some require that you specify the > state machine in a high level text based language. Others that allow you > to use diagrams. Some will only generate complex C++. Others that will > generate C. But I haven't come across any (other than ZMech) that will > allow you to produce machine executable code and interactively debug it > directly against the state diagrams. > > Going back to the alternate multi-tasking approach, there is the XCSB > compiler which produces highly efficient machine code executables. The > language has multi-tasking built into it and the compiler generates task > safe function calls without resorting to the runtime overhead of a dynamic > stack and multi-tasking library. > > The LITE edition of XCSB if free for hobbyist / student use > (non-commercial) and you can get it from: > > http://www.xcprod.com/titan/XCSB > > The following might give you some ideas that you can either implement > yourself (maybe with paper and pencil) or things to look out for in an > automated dev tool: > > http://www.xcprod.com/titan/ZMECH-DOC/generate/state-machine/block-indx.html > > Regards > Sergio Masci >

On Apr 22, 2008, at 10:17 AM, Martin wrote: > more like a system-level design where you might have a timer- > interrupt drive a state machine that would accomplish 10 different > tasks that you have to do? John Peatman's "Embedded Design with the PIC18452 Microcontroller" is rather like that. He starts by introducing a timer tick that "goes off" every 10ms, and adds different peripheral support functions as you go through the book. (The tick starts out NOT being interrupt driven...) The book is pretty expensive, and I didn't like it very much (I considered it to spend too little time on understanding the instruction set), but I think I'm willing to concede that it's a valid perspective on systems level usage. There are a couple of chapters online at http://www.picbook.com BillW

Hi Martin, The following is a work in progress but may be of help: http://www.xcprod.com/titan/state_machine.pdf Regards Sergio On Tue, 22 Apr 2008, Martin wrote: {Quote hidden}> Are there any good books or resources that you would recommend about > designing software on the PIC? I don't mean "this is how you make an LED > blink" or "this is how you drive a stepper motor" but more like a > system-level design where you might have a timer-interrupt drive a state > machine that would accomplish 10 different tasks that you have to do? > (just an example, I don't know if that's how you'd actually do it) > > Also I've had a quick look at the likes of FreeRTOS - but I'm using > assembly. I feel like the only benefit of using C would be that my code > is more organized and perhaps quicker to develop (but then there'd be > low level bugs I can't see easily) > > Does anyone use an RTOS with assembly in their PIC 18F project? Would it > be very difficult to write some time-sharing code for a PIC? > > - > Martin

On Fri, 25 Apr 2008, Dario Greggio wrote: > sergio masci wrote: > > > The following is a work in progress but may be of help: > > > > nice and clear, thank you Sergio. I've updated the document and given it a web page of its own so that you can now check for updates without having to download the entire document every time. I've added info to help the inexperienced understand how to draw a state diagram avoiding critical event order and how to debug a state diagram and add missing states. It is still a work in progress and there is still much to cover. You can download the latest version of this ebook from: http://www.xcprod.com/titan/state_machine_ebook.html If you find this ebook useful then please place a link to its web page on your web site. Thanks. Regards Sergio

On Mon, 28 Apr 2008, Rikard Bosnjakovic wrote: {Quote hidden}> On 28/04/2008, sergio masci <.....smplxKILLspam@spam@allotrope.net> wrote: > > > You can download the latest version of this ebook from: > > > > www.xcprod.com/titan/state_machine_ebook.html > > Sergio, > > This work of yours is a remarkable piece of document. Knowing nothing > about state machines, I read it page by page and can't wait for the > next version to see who the murderer is. > > Or seriously, while I'm not having the need for a state machine at > this time the document introduced me a few interesting ways of > debugging, something which I welcome a lot. For the skilled, the > document is probably on a too low level but for a "zero knower" it's > perfectly levelled without being too basic. > > Keep up the good work! Thank you.