Extension of the SAMD21 port.

[robert-hh]

Now that external flash support is enabled, how should the extra 64k flash space used at SAMD21 devices. Options:

• Use LFS2 instead of LFS1: 6k
  Observation: Using LFS2 in addition to LFS1 increases the flash by 16k. That's strange.
• Framebuffer support: 4k
• Set Python feature level to FULL_FEATURES instead of CORE_FEATURES: 25k
• Support onewire, dht_readinto with scripts: 3.5 k
• Complex math: 3.2 K (not yet enabled for SAMD51)
• UART flow control 300 Bytes
• Viper and Native code: 21k
• More frozen bytecode by default.

The available RAM did not grow. So using a lot of static data is bad,

[rkompass]

6k + 16k + 4k + 25k + 3.5k + 3.2k + 0.3k +21k = 79k < 80k = 64k + 16k ???. I would then suggest to include all of the above options.

[robert-hh]

The LFS options are either 6k OR 16k, not both. And CMATH support may be questionable, since it is not enabled at SAM51.
So with LFS2 only and no CMATH it adds to ~60k. It still should be considered that the SAMD21 is pretty low on RAM, like 20k for the heap.

[rkompass]

Then it probably also makes no sense to include framebuffer support, as it is not a device one would choose to attach an LCD to.

[ricksorensen]

How many SAMD21 boards have the external flash? (the itsybitsy and feather boards do I see).

I would think for those SAMD21 boards without WiFi/BLE/.. the framebuffer should be included for basic display of changing info. I use a small I2C OLED for GPS and simple environmental app using a SAMD21 without external Flash for example. I add framebuf to my build which reduces my onboard flash filesystem to 48K.

And sensor processing options (dht, onewire) ... And code(speed) optimizations (Viper, Native) could be useful for lower power MCUs.

I would bias onboard usage towards the compiled C code since the added external Flash gives room for python code.

My 2 cents, if even that.

[robert-hh]

I made a first package including:

• Set Python feature level to EXTRA_FEATURES instead of CORE_FEATURES.
  EXTRA_FEATURES was needed to enable Viper & Native, but less may be possible. I have to check what exactly is needed.
• Viper and Native code. While on a relatively slow device Viper and Native code is helpful, it might not need all MicroPyton features.
• Support onewire, dht_readinto
• Framebuffer support
• UART flow control