Following on from my other question, Help optimising this C (AVR) code? :), I just realised that I don't really know the mechanics of how to implement an ISR in assembly within my C program. I googled, but I didn't find anything too useful.
Basically I want to set up everything else in my C project (including the registers to get the interrupt to fire), but I want the interrupt to execute some assembly code that I've written.
I'm using AVR studio 6 on Windows if that helps. I've been told I need to use .s files but apart from that I'm not really sure what to do. Is the basic structure just the following?
#include <avr\io.h>
TIMER1_COMPA_vect:
; assembly instructions here
If I want the assembly to run when the TIMER1_COMPA_vect interrupt is fired (this is the name of the ISR in C). Or am I totally off track? What is a basic template of what I need to do? Or if it's a dumb question, is there a link where I can find more information?
The Art of Assembly Language (by Randall Hyde) has two chapters about ISRs (17th and 18th, specifically sections 18.5 and 18.6 might help you). Shortly:
Go to the IVT (interrupt vector table) and modify it with your ISR segment and offset, saving the old values
You should do a TSR (terminate and stay resident) program, so that your ISR stays resident into memory even when the user closes the window
Remember to call the old ISR after you're done with the work (this is called interrupt chaining)
your ISR should be re-entrant (so that if the interrupt is fired again when your ISR is still running the pc won't explode ;) )
By the way, you can obtain a pdf copy of that great book here
Related
I'm currently trying to implement interrupts on the STM32L152. I'm not using the standard peripheral libraries because I find them very confusing and difficult to get my head around. I'm not too competent with C for micro controllers yet.
I currently do everything through registers. Is there a way to implement interrupts in C through registers? There doesn't seem to be any information that actually makes sense out there. I did find learning C to be very inaccessible in the first place tbh.
Thanks
Of course you can implement interrupts by setting registers.
The registers-values tell the STM how to deal with interrupts, which interrupt is enabled, how the interrupt-controller has to work.
You'll need an Interrupt-vector-table. When an interrupt occurs a the program-counter will be set to an specific address of program-memory. There you should place a jump-command (assembler jmp) to your interrupt-service-routine.
You should read chapter 10 in this reference manual.
Hope this helps.
I'm going through how FIQ works on ARM and came across the statement that FIQ should always be written in assembly not in C but couldn't understand why?
I have gone through the following link
http://comments.gmane.org/gmane.linux.ports.arm.kernel/14004
But still couldn't make out why is it required?
Can any one please point me out the need of writing FIQ in assembly through some example?
My guess is based on this:
Also, it's a little difficult to write the FIQ code in C, since you lack a stack :)
If there's no stack, that would mean that the compiler is restricted to only using registers for all variables, which I'm not sure how you'd even express.
You can put register on all the local variables, but that doesn't mean that the compiler has to comply.
Writing the code in assembly of course goes around this restriction, and makes it possible to combine registers and global state to do things.
See also this question's answers for more about the difference between an ordinary interrupt and a fast one.
Because what is the point, you are using an extra bank of registers to save a handful of clock cycles in saving the state, then to use C and completely blow that tiny cost savings? If you are not interested in optimizing to that level then dont bother with fiq just use irq.
Basically , I want to know What an ARM Simulator is ? IS it something like an Assembly language simulator ? If so what are the differences in comparison with Verilog Simulators?
Your question is quite broad/vague. but here goes.
An arm simulator, from the context of what you are asking, is likely an instruction set simulator. Software that just like a processor decodes the instructions, keeps track of the registers, and simulates the execution (if an instruction says add 1 to r1 then you have a variable in software that represents r1 and you add one to it).
A verilog simulator, is not really any different just a different language. verilog is a hardware design language, before you can simulate it you need to compile it. Just like any other high level language it needs to be compiled down to something related to the target. simulators will have their own target logic blocks. The verilog is compiled down to these blocks then that logic is simulated, not unlike the arm simulator. For each clock cycle you update the inputs to each logic element based on the output of the connected block from the prior cycle, then evaluate each logic element and determine the outputs. repeat forever. for each verilog simulator you have a different target at its core, partly why you (can) get different results from each simulator for the same code. Likewise when you compile for the actual target, fpga, asic, etc, it is compiled differently than the simulator (or can be, depends on the environment, simulator, etc).
There is no magic at all to any of these simulators, an instruction set simulator is generally easy to write, a worthwhile task for anyone wanting to get a good strong knowledge of an instruction set or how computers work (start with something small like lc-3, should take less than half an hour). A FAST simulator, that is another story, but a FUNCTIONAL simulator is fairly easy to write. Once compiled to a netlist of simple logic components a verilog simulator is probaby easy as well the biggest task though is the volume of signals and items to evaluate and parsing the code to get at the list of signals and logic functions and who is tied to what. Not as easy as an instruction set simulator, but quite understandable how it works and what the task would be...Verilator is pretty cool as it turns it into lines of C++ code, MANY lines, and a good sized project can take many hours to days to compile even on a screaming machine. (hint turn off waveforms to cut the compile time way down). But the task is understandable when you look at what is going on.
For the life of me I can't make a timer for PIC18 or precisely PIC18f87j11. All I want to do is to have a counter that increments every 1 second. I just want to monitor how long PIC18 been running in terms of seconds.
Most of the tutorials out there are for PIC16 and are in assembly. I am trying to do this using C programming. For someone who is beginner I understand better if I see examples, so without examples I can't progress.
please someone show me an example, thank you!
To begin understanding timers you will need to have a look at their documentation. I suggest searching the manufacturers website. There are 5 timer available. If you use Timer0 which is either a 8 bit or 16bit timer. You will need to set the correct configuration for T0CON. Also you will need to have correct interrupt settings (INTCONbits), so a an event can be generated by interrupt service routine once timer expired.
You will most likely need to calculate the prescale value you require for correct timing, in your case 1 second. It does depend on FOsc: Here is a tutorial
Here an example of C code using MPLab and another one based on MPLab and hi-tech compiler. It is not for same chip, however it is based on PIC18F family.
It's been a awhile since I have visited PIC18F, so if any correction required, please do so.
If you use HIGH-TECH compiler, you can simply use its special function for close, open, read and write timers modules in below directory:
...\HI-TECH Software\PICC-18\9.80\sources\plib\Timers
According to your microcontroller name, you can figure out which version of these function is written for your microcontroller. So for first step, open pconfig.h file and search your microcontroller name to see for every module which version is fit to your microcontroller registers.
Good Luck
I have AT91Bootloader for AT91sam9 ARM controller. I need add some extra hardware initialization, but I have only compiled .bin file.
I loaded bin file to memory and tried to call it:
((void (*)())0x00005000)();
But, haven't any results. Please use assembler as less as possible. I was introduced to assembler before, but cannot understand ARM assembler due to it's complicity. How can I make call from middle of bootloader, execute bin file (it will be in some memory sector, 0x00005000 for example) and then return to bootloader and continue executing it's own code?
If ARM asm is "too complex", you will find it very difficult to debug any problems you're having. Basic* ARM assembly is one of the least complex assembly languages I've come across.
Your code ought to work (though I would not use a hard-coded address there) provided the ".bin" is of the correct format. Common issues:
The entry point should be ARM code; some compilers default to Thumb. It's possible (if a little tricky) to make Thumb code work.
The entry point needs to be at the start of the file. Without disassembling, it's hard to tell if you've done this correctly.
The linker will insert "thunks" (a.k.a. "stubs") where necessary. A quirk in some linkers means that the thunk can be placed before the entry point. You can work around this by using --stub-group-size=-1 (docs here).
* Ignoring things like Thumb/VFP/NEON which you don't need to get started.
ARM assembly is one of the simpler ones, very straight forward. If you want to continue to do bare metal you are going to need to learn at least some assembly. For example understanding Alexey's comment.
The instruction you are looking for is BX, it branches to an address, the assembly you need to branch to the code your bootloader downloaded is:
.globl tramp
tramp:
bx r0
The C prototype is
void tramp ( unsigned int address );
As mentioned in the comments the program needs to be compiled for the address you are running it from and/or it needs to be position independent, otherwise it wont work. Also you need to build the application with the proper entry point, if it is raw binary and you branch to the address where the binary was loaded the binary needs to be able to be started that way by having the first word in the binary be the entry point for execution.
Also understand that an elf format file contains the data you want to load, but as a whole is not the data you want to load. It is a "binary file" yes but to run the program contained in it you need to parse and extract the loadable portions and load them in the right places.
If you dont know what those terms mean, use google, and/or search SO, the answers are there.