For <512k targets, ESC passthrough for non-BL Heli ESCs ESCs fails

[Vanja-APD]

Describe the bug

Connection to passthrough ESCs using BF4.3+ fails with non-BL Heli ESCs due to a change in connection string format. The issue appears within RC1 of 4.3, appears to be a compile-time define (USE_SERIAL_4WAY_SK_BOOTLOADER) which affects the connection string format is now guarded by a flash_size check. Imagine below shows the changes.

https://github.com/betaflight/betaflight/commit/82b5e386f39465905c6dbdecbe2e1ee744efe000

Is it possible to reverse this change, or is there a reason for this protocol change?

Thanks!

To Reproduce

Install BF4.3 onto FC, attempt ESC passthrough configurator connection to non BLHeli, non-SK ESC. No issues with prior versions of BF (4.2x).

Expected behavior

USE_SERIAL_4WAY_SK_BOOTLOADER macro remains defined as per previous versions of BF releases.

Flight controller configuration

  # REPLACE THIS LINE BY THE OUTPUT OF YOUR `diff`

  # REPLACE THIS LINE BY THE OUTPUT OF YOUR `resource show all`

Flight controller

FC Invariant (reproduced on multiple)

Other components

No response

How are the different components wired up

No response

Add any other context about the problem that you think might be relevant here

No response

[DusKing1]

Removed due to firmware size

[haslinghuis]

@daleckystepan @SteveCEvans I think this is important for the use case. How much memory did this save? Do we have room to get it back?

[daleckystepan]

Enabling USE_SERIAL_4WAY_SK_BOOTLOADER adds more than 1.5kB FLASH on F722 or F411.

[haslinghuis]

Yeah this really shows the end of 512K targets. Do we have still have some space left to support this method a little longer otherwise we can close it as unsupported target or too old? Is this not needed for AM32 etc?

[daleckystepan]

Current master

Linking STM32F7X2 
Memory region         Used Size  Region Size  %age Used
        ITCM_RAM:       16256 B        16 KB     99.22%
     AXIM_FLASH1:      445563 B       480 KB     90.65%

and

Linking STM32F411 
Memory region         Used Size  Region Size  %age Used
          FLASH1:      488183 B       480 KB     99.32%

It will probably fit but it is very tough - we will not be able to add something more (and maybe more important). On the other hand it's regression. GCC11 will help us slightly.

[haslinghuis]

🤞 it might be important for manufacturers and esc firmware development

[klutvott123]

If we were to include this again, we would only have to remove something else. I'm sure manufacturers and firmware developers can include it and compile on their own

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs within a week.

[github-actions]

Issue closed automatically as inactive.