Improve available heap

[devyte]

Hardware

Hardware: all Core Version: git / 2.4-rc2

Problem Description

Summary

This issue is meant to track a RAM optimization effort. The goal is to increase available RAM as much as possible.

Details

The following are initial ideas to investigate.

• Move all const char strings to flash, and use the the access macros to access them. Implement alternate methods/functions with the correct argument signatures where applicable. This covers both the core as well as the Arduino lib code.
• Move const declarations to flash. Example: CHARS_PER_LINE in libb64/cencode.c.
• Revise all singleton object declarations. Make sure that all are wrapped by #defines that allow compile-time configuration to not use the global singletons. Example: Use of the Serial, but not Serial1, frees up 256+ bytes of heap.
• Revise all uses of constant size char [] arrays. Arrays like that should not be declared on the stack, but rather created dynamically, and only on demand. Example: 2K buffer in ESP8266Webserver. -Revise all uses of String. When concatenating, the internal managed array will grow, sometimes far beyond what is needed. It is sometimes better to reserve, if there is an estimate of how much space will be needed.
• Revise object implementations. Make sure objects are passed by reference or pointer, and never by copy.

[devyte]

@steminabox about floating point support, you misunderstood me: it was not put into IRAM, it was just added to the code base. I meant it as an example as to why the core is always increasing in size: features are being added. If you search the code for ICACHE_RAM_ATTR, you'll find all the functions in the core that are specified to be in IRAM, and if you think about each case you'll understand why they have to be there. Those are not all, though, there are parts of the SDK that have to be in IRAM as well, among others. But we're getting off topic. This thread is meant to cover increasing free heap, which is the single biggest obstacle right now for secure sockets. The IRAM issue is a different one, and there is a discussion already ongoing elsewhere. So if you have an idea about improving free heap, bring it up here.

[steminabox]

yep, I'll continue about IRAm in the other thread, though having infinite heap and no ability to load your program isn't that useful :-)

So my last comment, actually on topic :-) - with the heap the best way to keep spare space is to never use memory unless you have to, defer it until the last moment, and keep for as short as time as possible.. There is normally a trade off with doing this and cpu time (and mem fragmentation)- but the 8266 seems to have lots of cpu for the amount of memory it has.. I don't know if fragmentaion would be a problem, then again, most 8266s could reboot every now and again..

[devyte]

A lot has been done for this, but there is still more to do...