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Severe problem with printf and interrupt

 
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Zer0flag
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Severe problem with printf and interrupt
PostPosted: Wed Apr 16, 2008 4:17 am     Reply with quote
Hi all!

In my program I have implemented a temperature PI Controller routine in a timer interrupt in order to achieve equidistant calls. So there are a couple of calculations (including 32 bit divisions and multiplications) as well as reads and writes to the SPI bus in this interrupt. I know one should not put so much stuff in the interrupt but I didn't find a possibility to implement equidistant calls in the main loop and there are no other critical interrupts so I did it that way.

Now I notice a severe problem with printf trying to output a 32 bit integer in the main program as long as the PI Controller interrupt is enabled.

The following code:
Code:

printf("%Lu", (int32) 0);


outputs most of the time 0 but from time to time it outputs something else. I also tested the whole thing with a 32 bit variable (instead of the hardcoded 0) and with numbers other than zero and the problem persists. Strangely with int16 I don't see the problem.

If I disable the PI Controller interrupt around printf everything works ok.

Printf is not called in my interrupt but I think there might be some functions used by printf that are also used in my interrupt (e.g. some calculation functions) that are not reentrant or something and they get messed up when the interrupt occurs at a specific point in time during the printf.

Any help is welcome!

Best regards,
Zer0flag
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Wed Apr 16, 2008 11:21 am     Reply with quote
Are you using the hardware UART or a software emulated UART? Prove this by posting the chip number and the #use rs232 line.

In case you are using the hardware UART, than notice that on most chips this is double buffered. This could be a partial explanation of why a 2-byte int16 always succeeds and a larger message sometimes fails.
Zer0flag
Guest
PostPosted: Wed Apr 16, 2008 2:34 pm     Reply with quote
ckielstra wrote:
Are you using the hardware UART or a software emulated UART? Prove this by posting the chip number and the #use rs232 line.

In case you are using the hardware UART, than notice that on most chips this is double buffered. This could be a partial explanation of why a 2-byte int16 always succeeds and a larger message sometimes fails.


Hi!

This is the PIC and UART stuff:

Code:

#include <18F4620.H>
#use rs232(baud=19200, parity=N, bits=8, stop=1, xmit=PIN_C6, rcv=PIN_C7, ERRORS)


The problem is that calling printf with another function like:

Code:

printf(bputc,"%Lu", (int32) 0);


or

Code:

printf(lcd_putc,"%Lu", (int32) 0);


results in the same error.

sprintf() also gives the error described in my first post.
itoa() in contrast does not give an error.

Regards,
Zer0flag
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