70 lines
2.9 KiB
Text
70 lines
2.9 KiB
Text
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The purpose of this library is to give the programmer the ability to add interrupts
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with the easy of attachInterrupt, which looks like this:
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attachInterrupt(interrupt, &function, MODE)
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...the interrupt is a number which gets translated to the proper pin on the Arduino. For example,
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Board int.0 int.1 int.2 int.3 int.4 int.5
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Uno, Ethernet 2 3
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Mega2560 2 3 21 20 19 18
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Leonardo 3 2 0 1 7
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Due (doesn't use interrupt numbers, it uses the pin numbers directly)
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The MODE is LOW, CHANGE, RISING, or FALLING. On the Due board, you also have HIGH.
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The PinChangeInterrupt library does not work on the Due; it is not necessary. It is somewhat easier
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to use than attachInterrupt() because you don't have to translate from an "Interrupt number" to a
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pin number- you simply give it the pin that you want to Interrupt on:
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PCintPort::attachInterrupt(interrupt, &function, MODE)
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The MODE is LOW, CHANGE, RISING, or FALLING. On the Due board, you also have HIGH.
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To have an Interrupt:
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Global Interrupt flag must be enabled.
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Set the I-bit in SREG.
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In PCICR: bit 2 == PCIE2: set, enable pins PCINT[23:16], enable individual by PCMSK2
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bit 1 == PCIE1: set, enable PCINT[14:8], enable individual by PCMSK1
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bit 0 == PCIE0: set, enable PCINT[7:0], enable individual by PCMSK0
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Pin Change Interrupts and Other Libraries ============================================================
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Serial.print()----------------
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Serial.print() does not work well inside interrupts. This is because it uses interrupts,
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and while you are in an interrupt, interrupts are (by default) turned off.
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Serial is declared in /usr/share/arduino/hardware/arduino/cores/arduino/HardwareSerial.h .
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In the write() method in the .cpp file, for example it says:
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...
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// If the output buffer is full, there's nothing for it other than to
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// wait for the interrupt handler to empty it a bit
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// ???: return 0 here instead?
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while (i == _tx_buffer->tail)
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;
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...
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And the ISR is further down in that file (this for the ATmega328 I believe):
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ISR(USART_RX_vect)
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...
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If a user wants to try to use Serial.print() inside an ISR, I believe it's possible
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(by turning on interrupts inside the interrupt)...
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but it would require them to be aware of any possible contention between the interrupts,
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and the print ISRs.
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Software Serial----------
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The SoftwareSerial library defines ISRs for Pin Change Interrupt ports:
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ISR(PCINT0_vect)
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{
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SoftwareSerial::handle_interrupt();
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}
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...It defines the interrupt on all ports, whether it's using them or not
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(the library cannot know ahead of time if the user will be using a set of pins
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or not).
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To ensure compatibility with the SoftwareSerial library, the user should comment
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out the ports that they are NOT using with the SoftwareSerial library, in
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/usr/share/arduino/libraries/SoftwareSerial/SoftwareSerial.cpp
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and comment out the ports that they ARE using with this library in PinChangeInt.h
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