PSA: Current RPI3B+ Firmware reduces CPU throttling temp to address stability problems

[dankcushions]

see https://forum.kodi.tv/showthread.php?tid=298461&pid=2739911

We've tweaked avs and sdram settings to hopefully fix issues with some of the borderline RPi3+ boards.

One change is we no longer add "sdram_schmoo=0x02000020" and "over_voltage_sdram_p=2" on a Pi3+ when sdram_freq > 450 (we do for older Pi's). If anyone with sdram overclock who doesn't explicitly set those reports a problem, then suggest adding them (one at a time).

Another change is when overclocking sdram, we should really be increase the RL/WR values (read latency/write latency) which we will now do. It has a small effect on performance, but shouldn't affect a busy system much (other accesses can get in during the gaps).

One other change with new firmware is the temperature threshold when we switch from 1.4GHz to 1.2GHz has been reduced from 70'C to 60'C. This may produce some reduction in performance when chip is hot, but it makes some of the borderline boards reliable. It can be overridden with temp_soft_limit=70 to get back to previous behaviour.

i believe the current version of retropie precedes this version, so unless you've updated via sudo apt-get dist-upgrade, etc, you will not have this firmware. however, later versions will surely have it. it also seems these changes are specific to the 3B+, so regular 3Bs are operating as normal.

personally, since i don't use my RPI3B+ to do Kodi or any other CPU intensive, multicore tasks (emulation is typically single core), i am going to revert back to previous throttling behaviour to my /boot/config.txt and see if i get any issues. i had none before!

temp_soft_limit=70