When the "autoscroll" checkbox is deselected the buffer may continue
to grow up to twice of the maximum size.
This is a compromise to ensure a better user experience and, at the
same time, reduce the chance to lose data and get "holes" in the
serial stream.
See #2491
Before this patch every byte received from Serial
invokes a String allocation, not really efficient.
Moreover a InputStreamReader is chained on the serial
InputStream to correctly convert bytes into UTF-8
characters.
Previously, it could happen that SPI::beginTransaction was
interrupted by an ISR, while it is changing the SPI_AVR_EIMSK
register or interruptSave variable (it seems that there is
a small window after changing SPI_AVR_EIMSK where an interrupt
might still occur). If this happens, interruptSave is overwritten
with an invalid value, permanently disabling the pin interrupts.
To prevent this, disable interrupts globally while changing
these values.
From https://github.com/arduino/Arduino/pull/2376#issuecomment-59671152
Quoting Andrew Kroll:
[..this commit..] introduces a small delay that can prevent the wait
loop form iterating when running at the maximum speed. This gives
you a little more speed, even if it seems counter-intuitive. At
lower speeds, it is unnoticed. Watch the output on an oscilloscope
when running full SPI speed, and you should see closer back-to-back
writes.
Quoting Paul Stoffregen:
I did quite a bit of experimenting with the NOP addition. The one
that's in my copy gives about a 10% speedup on AVR.
It reads the state of a potentiometer (an analog input) and turns on an LED
only if the LED goes above a certain threshold level. It prints the analog value
regardless of the level.
updated to
It reads the state of a potentiometer (an analog input) and turns on an LED
only if the potentiometer goes above a certain threshold level. It prints the analog value
regardless of the level.
