Regression of max sketch size for nano33ble with 0.54.1

[lyusupov]

Build of any sketch for nano33ble target fails with 0.54.1 when the sketch binary size exceeds 98304 bytes.
Build is fine when 0.53.1 is in use.

To reproduce

$ arduino-cli core install arduino:zephyr_main@0.53.1
$ cd ~/.arduino15/packages/arduino/hardware/zephyr_main/0.53.1/
$ grep nano33ble.upload.maximum_ boards.txt
nano33ble.upload.maximum_size=1966080
nano33ble.upload.maximum_data_size=523624
nano33ble.upload.maximum_size=786432
nano33ble.upload.maximum_data_size=523624

$ arduino-cli core install arduino:zephyr_main@0.54.1
$ cd ~/.arduino15/packages/arduino/hardware/zephyr_main/0.54.1/
$ grep nano33ble.upload.maximum_ boards.txt
nano33ble.upload.maximum_size=98304
nano33ble.upload.maximum_data_size=131072
nano33ble.upload.maximum_size=98304
nano33ble.upload.maximum_data_size=131072

Curiously, the maximum_size value is fine in the repo boards.txt file: https://github.com/arduino/ArduinoCore-zephyr/blob/main/boards.txt#L123

Highly likely that the wrong value gets applied by the 0.54.1 packaging script.

[pillo79]

Thanks for looking into this! Those limits have indeed changed from 0.53, but unfortunately this is the correct behavior. The compiled sketch must fit into the user_sketch partition, which for the Nano 33 BLE is defined as:

ArduinoCore-zephyr/variants/arduino_nano_33_ble_nrf52840_sense/arduino_nano_33_ble_nrf52840_sense.overlay

Lines 32 to 35 in 7dbd415

	user_sketch: partition@e0000 {
	label = "user";
	reg = <0x0e0000 0x18000>;
	};

... and 0x18000 is exactly the number the packaged file is reporting.

The numbers in the Git version of boards.txt are not meaningful - they were just set to some big value to avoid this test kicking in. They are going away shortly - #381 we will introduce even more precise limits to get the maximum out of your boards.

[lyusupov]

@pillo79

Please, explain why only 98304 bytes out of 1 Mbyte flash memory space available in Nordic nRF52840 ( nano33ble ) are permitted to be assigned for a user sketch since 0.54.1 ?

This is an example of a memory map in use by Arduino Core for nRF52 Series developed by Adafruit Team:
https://github.com/adafruit/Adafruit_nRF52_Arduino

[facchinm]

@lyusupov the choice is a tradeoff to leave more space for the loader (zephyr operating system). The sketches will not be as big as with other cores since all the drivers and heavy libraries will live in the loader space.
However, right now the loader is greatly oversized (last code build)

Memory region         Used Size      Region Size    %age Used
FLASH:                270408 B       832 KB         31.74%

I think we could split the flash 50% / 50 % without much trouble.
@pillo79 @maidnl @dani-clo do you agree?