Merge pull request #7673 from mikeller/publish_feature_freeze_announcement

Updating README.md and the pull request template for the feature freeze / STM32F3 retirement.

.github/pull_request_template.md

@@ -1,3 +1,14 @@
+## Important: Feature freeze / release candidate phase for Betaflight 4.0
+
+From 01 Mar 2019 until the release of Betaflight 4.0.0 (scheduled for 01 Apr 2019), the project is in a 'feature freeze / release candidate' phase. This means:
+
+1. Pull requests can still be submitted as normal. Comments / discussions will probably be slower than normal due to shifted priorities;
+
+2. If your pull request is a fix for an existing bug, or an update for a single target that has a low risk of side effect for other targets, it will be reviewed, and if accepted merged into `master` for the 4.0 release;
+
+3. All other pull requests will be scheduled for 4.1, and discussed / reviewed / merged into `master` after 4.0.0 has been released. Please keep in mind that this potentially means that you will have to rebase your changes if they are broken by bugfixes made for 4.0.
+
+
 ## Important: Embargo on new targets for Betaflight 4.0
 
 As announced earlier in https://github.com/betaflight/betaflight#betaflight-40, Betaflight 4.0 will introduce a radically new way to define targets. At the moment, we are making the changes necessary for this, and this requires some changes to how targets are defined in the 'legacy' way. Because of this, any pull request opened against `master` that introduces a new target is likely to be outdated by the time it has been reviewed. This means extra work for the target maintainer and the reviewers, for little or no benefit.

README.md

@@ -1,4 +1,9 @@
-![Betaflight](https://raw.githubusercontent.com/wiki/betaflight/betaflight/images/betaflight/bf_logo.png)
+![Important Notice: Betaflight 4.0 will be the last release to include support for STM32F3 based flight controllers. (This includes all boards with 'F3' in the name.)](docs/assets/images/stm32f3_retirement_notice.svg)
+
+(Please see the [note](https://github.com/betaflight/betaflight#end-of-active-development-for-stm32f3-based-flight-controllers) below.)
+
+
+![Betaflight](docs/assets/images/bf_logo.png)
 
 Betaflight is flight controller software (firmware) used to fly multi-rotor craft and fixed wing craft.
 
@@ -6,6 +11,16 @@ This fork differs from Baseflight and Cleanflight in that it focuses on flight p
 
 ## News
 
+### End of active development for STM32F3 based flight controllers
+
+For a while now, development of Betaflight for flight controllers based on the STM32F3 chip has been hampered by a severe limitation that this chip has: Unlike the STM32F4 and STM32F7 models, the STM32F3 versions that are used on flight controllers have only a very limited amount of flash space available to fit the firmware into. This has meant that, starting from around version 3.3, the majority of the new features that were developed for Betaflight could not be added to STM32F3 based boards. Even worse, due to improvement in basic features, other more and more of the less commonly used features had to be removed from these flight controllers, and a number of them are at a point where they only support the bare minimum of functionality required to make them fly.
+
+This means that, even if we kept supporting STM32F3 based boards in future releases, there would only be little advantage in this, as there simply is no space left on STM32F3 to add any of the new features that these releases will contain.
+
+For this reason, and because the effort required to remove features from STM32F3 based flight controllers on a weekly basis is cutting into the time that we have to actually develop new features, we have decided to drop support for STM32F3 based flight controllers after the last release of 4.0.
+This does not mean that it won't be possible to use these flight controllers after this point in time - they will still work fine when used with the last release of 4.0, just as there are thousands of users who are still enjoying their STM32F1 based flight controllers with Betaflight 3.2.5. We will also strive to keep these versions supported in new releases of configurator, so that users still using these flight controllers will be able to configure them with the same configurator that they use to configure their STM32F4 and STM32F7 based boards.
+
+
 ### Embargo on new targets for Betaflight 4.0
 
 As [announced earlier](https://github.com/betaflight/betaflight#betaflight-40), Betaflight 4.0 will introduce a radically new way to define targets. At the moment, we are making the changes necessary for this, and this requires some changes to how targets are defined in the 'legacy' way. Because of this, any pull request opened against `master` that introduces a new target is likely to be outdated by the time it has been reviewed. This means extra work for the target maintainer and the reviewers, for little or no benefit.

docs/assets/images/stm32f3_retirement_notice.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="800px" height="120px" viewBox="0 0  800 120" preserveAspectRatio="xMidYMid meet" ><rect id="svgEditorBackground" x="0" y="0" width="800" height="120" style="fill: none; stroke: none;"/><text style="fill:black;font-family:Arial;font-size:20px;" x="283" y="144" id="e1_texte"></text><rect x="0" y="0" style="fill:#feafa8;stroke:red;stroke-width:5px;" id="e2_rectangle" width="800" height="120"/><text style="fill: black; font-family: Arial; font-size:24px;font-weight:bold;" x="30" y="15" id="e3_texte" dx="0" dy="24"><tspan x="397.8984375" style="text-anchor:middle;">Important Notice: Betaflight 4.0 will be the last release to include</tspan><tspan style="text-anchor:middle;" x="397.8984375" dy="1.25em">support for STM32F3 based flight controllers.</tspan><tspan style="text-anchor:middle;" x="397.8984375" dy="1.25em">(This includes all boards with 'F3' in the name.)</tspan></text></svg>