jerpelea opened a new pull request, #16687: URL: https://github.com/apache/nuttx/pull/16687
## Summary AVR is a Harvard architecture with separate address spaces for program and data memory. Unless the compiler is instructed otherwise, C pointers are always referring to the data memory. Variables declared with const must therefore be copied to RAM to be accessible - which is undesirable since RAM is a limited resource on these chips. There are other approaches that can be taken but they are either not supported in NuttX or the support is quite limited. (These approaches are described in the document added in patch 0002 and adding full support for them would require fairly disruptive changes so that is unlikely to happen.) Newer chips offer an alternative solution - part of the program memory (a 32kB window) is mapped into data memory address space. Const variables can be placed into this window, making them accessible while using standard (data memory) pointers. This patch series adds support for this into both AVR architecture code and Breadxavr board. Series was tested by verifying string addresses - parameters in printf call in a custom application - in disassembly (and also by running the application and verifying its output.) Documentation was tested by HTML build. Short summary of the patches: 0001 - fixes Ctrl-C error in a comment, unrelated otherwise 0002 - adds a document that describes previously existing options of avoiding copying const variables into RAM 0003 - patch that makes use of the memory-mapped flash 0004 - ops structure in serial driver is marked as const ## Impact This patch series should not affect older AVR chips which do not have the memory-mapping. ## Testing AVR -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: commits-unsubscr...@nuttx.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
