We’re happy to announce the availability of the 2020.06 release! The release includes the Crazyflie firmware, the Crazyflie NRF firmware and the python library (0.1.11). You can find the full package in the Crazyflie Release repository, to be used for flashing through the python client.
More RAM
The major event of this release is the use of the Core Coupled Memory in the Crazyflie. The CCM is a 64k RAM memory bank and by moving memory blocks from the standar RAM to the CCM, we have freed up 64k of RAM! The 128k of RAM was almost full so an extra 50% is good news.
One might ask why this has not been done earlier and the answer is that the CCM has some special properties that has to be taken into account. It is RAM, just like the “normal” RAM, but it is connected to a different internal bus in the STM MCU. The most notable difference is that it can not be used in DMA operations that are commonly used when accessing sensors, and if a pointer to CCM memory is passed to a sensor driver things will go bad. To make it clear where the memory is located, we have introduced a macro to be used when explicitly moving a memory area to the CCM, otherwise it will end up in normal RAM.
Hopefully the chosen design will have very little impact on the “normal” firmware programmer. We have moved a bunch of memory blocks to the CCM that are “safe”, and most programmers can happily forget about the CCM and just enjoy the new 64k of available RAM!
Battery temperature
In release 2020.02 we introduces a battery temperature check do not charge the battery if it is too warm. Lithium batteries likes to be charged within 0-45 deg Celsius. To do this we used the temp sensor within the nRF51822 which is mounted just under the battery. It hover turned out that the temp measurement is way to biased and as a result stops charging to early. So in this release we did more measurements and increased the allowed charging range.