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Everything worked fine, except for the fact that the number in the register did not update until I put the entire chip to sleep, woke it up, and then started the counter again, after which it would update the register with the -previously- measured value from before when the chip was put to sleep.
You have to slaughter a chicken and sing a chant to get the data synchronized between the peripherials and the CPU, so that your processor actually gets the value you want to read off of your counter or your pin.įor example, I was trying to use a counter to count the number of pulses coming in through a pin. It exists, but it’s… complicated…Īll the features of the chip, such as hardware timer/counters and pin IO, are “peripherials” that sit on a shared “external” bus to the actual CPU, except some hardware which is also accessible through a dedicated bus, so low level access to the stuff gets weird really quickly.
#Guitar hero 3 wii unlockables how to#
It was very difficult to find any information about how to access the hardware directly like with the smaller AVR chips. When I was trying to get around the thing, all the other available examples were with ASF, which is a monstrosity. The problem is that the SAMD21 is somewhat complicated to program if you’re not using the Arduino libraries, so most people save themselves the pain and deal with the devil they know. Posted in Arduino Hacks, News Tagged adc, analogRead(), arduino, SAMD21 Post navigation If you don’t have an Arduino board with a SAMD21 uC, you can find out more about them here. We didn’t have a SAMD21-based Arduino available for testing before press time, but if you’ve got one handy and can replicate these experiments to verify the results, definitely let us know in the comments section below. There are instructions on the blog page on how to quickly test this bug. It seems odd to us that such a bug would go unnoticed for so long, but we’ve all seen stranger things happen.
That is enough to cause the observed offset issue.
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It turns out that the Arduino code doesn’t wait for the first, garbage, result to finish before starting the next one. That code disables the ADC between measurements, and when it is re-enabled for each measurement, the first result needs to be discarded. Still, having to correct for this level of error on a microcontroller ADC in 2019 - or even 2015 when the code was written - seems really wrong.Īfter writing their own ADC read routine that produced errors of only between 1 mV and 5 mV (1 to 6 LSB), the team turned their attention to the Arduino code.
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It seems like this offset was a known issue Arduino actually provides code to calibrate the ADC on SAMD boards, which will “fix” the problem with software gain and offset factors, although this can reduce the range of the ADC slightly. While developing a shield that interfaces to 24 V systems, the development team noticed that the ADC readings on a SAMD21-based board were off by a consistent 35 mV expanding their tests to a number of different analog pins and SAMD21 boards, they saw offsets between 25 mV and 57 mV. For a 12-bit ADC operating with a reference of 3.3 V, this represents a whopping error of up to 70 least-significant-bits! Excerpt from the SAMD wiring_analog.c file in the Arduino Core repo. In a recent blog post on, explains how they found a bug in the Arduino SAMD21 analogRead() code which causes the output to be offset by between 25 mV and 57 mV. The problem is, of course, that someone has to decode often cryptic datasheets to write that interface layer in the first place. Importantly, this isn’t just about language, but also about abstracting away the gory details of the underlying silicon. One of the great things about the Arduino environment is that it covers a wide variety of hardware with a common interface.
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