Update attachInterrupt.adoc #842
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Race hazards should be mentioned on this page. Nick Gammon's notes are misleading regarding single byte variables and I can't find any way to contact him easily.
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per1234
requested changes
May 7, 2022
| @@ -55,6 +55,40 @@ Generally, an ISR should be as short and fast as possible. If your sketch uses m | |||
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| Typically global variables are used to pass data between an ISR and the main program. To make sure variables shared between an ISR and the main program are updated correctly, declare them as `volatile`. | |||
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| Races, code which changes behaviour depending upon timing, can be a problem if both normal code and interrupt code tries to access variables at the same time. This leads to highly intermittent and hard to find bugs. The simplest solution is to disable interrupts when accessing shared variables from non-interrupt code. Interrupts are disabled by default in interrupt functions so unless interrupts are turned on there is no problem there. See `noInterrupts()` and `interrupts()`. | |||
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| Races, code which changes behaviour depending upon timing, can be a problem if both normal code and interrupt code tries to access variables at the same time. This leads to highly intermittent and hard to find bugs. The simplest solution is to disable interrupts when accessing shared variables from non-interrupt code. Interrupts are disabled by default in interrupt functions so unless interrupts are turned on there is no problem there. See `noInterrupts()` and `interrupts()`. | |
| Races, code which changes behaviour depending upon timing, can be a problem if both normal code and interrupt code tries to access variables at the same time. This leads to highly intermittent and hard to find bugs. The simplest solution is to disable interrupts when accessing shared variables from non-interrupt code. Interrupts are disabled by default in interrupt functions so unless interrupts are turned on there is no problem there. See `link:../../interrupts/nointerrupts[noInterrupts()]` and `link:../../interrupts/interrupts[interrupts()]`. |
Provide links to the reference pages the reader is being instructed to see.
| @@ -55,6 +55,40 @@ Generally, an ISR should be as short and fast as possible. If your sketch uses m | |||
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| Typically global variables are used to pass data between an ISR and the main program. To make sure variables shared between an ISR and the main program are updated correctly, declare them as `volatile`. | |||
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| Races, code which changes behaviour depending upon timing, can be a problem if both normal code and interrupt code tries to access variables at the same time. This leads to highly intermittent and hard to find bugs. The simplest solution is to disable interrupts when accessing shared variables from non-interrupt code. Interrupts are disabled by default in interrupt functions so unless interrupts are turned on there is no problem there. See `noInterrupts()` and `interrupts()`. | |||
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| Consider a common technique for interupts. The interrupt routine sets a flag which is acted on by code in the main loop. | |||
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Suggested change
| Consider a common technique for interupts. The interrupt routine sets a flag which is acted on by code in the main loop. | |
| Consider a common technique for interrupts. The interrupt routine sets a flag which is acted on by code in the main loop. |
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| If the interrupt occurs between testing the flag in line A and the clearing of the flag in line B then the flag will set by the interrupt and immediately cleared by the non-interrupt code resulting in the interrupt being ignored. The solution is to prevent the interrupt from interrupting at that critical point. |
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Suggested change
| If the interrupt occurs between testing the flag in line A and the clearing of the flag in line B then the flag will set by the interrupt and immediately cleared by the non-interrupt code resulting in the interrupt being ignored. The solution is to prevent the interrupt from interrupting at that critical point. | |
| If the interrupt occurs between testing the flag in line A and the clearing of the flag in line B then the flag will set by the interrupt and be immediately cleared by the non-interrupt code resulting in the interrupt being ignored. The solution is to prevent the interrupt from interrupting at that critical point. |
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Race hazards should be mentioned on this page. Nick Gammon's notes are misleading regarding single byte variables and I can't find any way to contact him easily.