OK, I have done some further research. I reinstalled the DFRobot Library that I had previously modified, back to the original downloaded from github. The DFRobot Library includes BME680.h and BME680.c files from BSEC version * @date 30 Oct 2017 * @version 3.5.3 (They are old and that is why I had replaced them with latest BME680 Library files.). I tried out 2 of the 4 example sketches. There is a basic sketch and a more elaborate sketch that reads IAQ. The basic sketch compiled OK, but the IAQ sketch did not. Same symptoms as noted previously (linker complaining about missing function code). I then look through several readme.md files within the folder structure of the library. Buried in Examnples was a folder 'docs for iaq'. Anyway within that folder a subfolder 'esp8266' and the attached BST pdf file, which is an (old ?) BSEC Imntegration guide dated 2017 for the BME680. I have attached this file. In that PDF, page 14 and 15 refer to the file libgobsec.a and tell the reader how it should be installed to allow the linker to find it. Now the ESP8266 is just one of many Arduino type processors in the market place. At the time the PDF file was written, (I guess) BSEC chose that processor as the one and only it supported, or maybe they just chose it as an example case in point. Whatever... It seems that since that time, BSEC have expanded the range of supported processors (as indicated in the current library documentation and library structure). However the current version of the integration guide dated 2019-06-28 I checked and found the exact same text. The text has not been updated to handle the expanded range of processors, and the latest versions of Arduino CC. The file libgobsec.a is currently not found by the arduino cc compiler/linker within the folder atmega2560 as might be indicated. Maybe the compiler/linker is not working as documented. I'm just guessing. I am not the only one having this trouble, I found other people compaining of the exact same issue over on the Arduino forum. Whatever the case, I would like you please to share with me instructions pertaining to the atmega2560 allowing me to manually modify the default bsec library and arduino CC installation to put the library in the correct location and modify appropriate files in similar manner to the esp8266 instructions given in the integration guide. I suggest you might also like to trigger an internal review within BSEC of the integration guide and have someone bring it up to date.
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