Merge in nrf52 support.

[tannewt]

From pull micropython#3137 if its not pulled upstream.

[ladyada]

• serial repl
• pin name/number in board
• digitalio module
• time module
• i2c support
• local flash storage - 128KB 92KB of internal flash
• random module

[microbuilder]

Local flash storage will have to be reduced to ~92KB assuming the following:

• 12KB Master Boot Record
• 48KB Serial Bootloader
• 140KB SoftDevice S132v5
• 28KB NFFS-based internal config memory (bonding data, etc.)
• 192KB CircuitPython Code

Remaining Space: 512KB - 420KB = 92KB local flash storage

[ladyada]

sounds fine to me - thats enough to get people going. our final design will have external SPI flash :)

[tannewt]

A couple naive questions from me:

• Why is the MBR 12k? Here its only 4k.
• Why is the bootloader 48k? Bossac and UF2 are only ~8k.
• Can we combine the NFFS filesystem with the file system for CircuitPython? Without USB we can use NFFS but we'll want FATFS for the USB version.

[microbuilder]

• For the MBR in that link 0x0..0x3000 = 12KB (???)

• The bootloader also supports OTA updates via BLE, which is why it's so large

• I will probably combine the two file systems internally yes (nRF52832 variants without USB), and simply hide the config files, but I always need to be sure that we have 'n' bytes free for storing the bonding data for up to 5 devices and other BLE config values, which is why for the moment I've kept them separate. This can be reduced to something smaller than 28KB, I just don't have the exact lowest safe number yet.

[microbuilder]

There is conflicting information about the sizes in the documentation. :(

I've listed below what seems to be the right/final settings for:

• S132 v2.0.1 (current feather52 boards)
• S132 v5.0.0 (future work and nRF52840)

S132 v2.0.1 with OTA DFU Bootloader

• CircuitPython Core: 228KB
• User Filesystem: 96KB
• Private Config Data: 28KB (which may get combined for 96+28=124KB total)

/*
    GNU linker script for NRF52 w/ s132 2.0.1 SoftDevice

    MEMORY MAP
    ------------------------------------------------------------------------
    START ADDR  END ADDR   SIZE    DESCRIPTION
    ----------  ---------- ------- -----------------------------------------
    0x00074000..0x00080000 ( 48KB) Serial + OTA Bootloader
    0x0006D000..0x00073FFF ( 28KB) Private Config Data (Bonding, Keys, etc.)
    0x00055000..0x0006CFFF ( 96KB) User Filesystem
    0x0001C000..0x00054FFF (228KB) Application Code
    0x00001000..0x0001BFFF (108KB) SoftDevice
    0x00000000..0x00000FFF   (4KB) Master Boot Record
*/

S132 v5.0.0 with OTA DFU Bootloader

The 5.0.0 SoftDevice adds Bluetooth 5.0 support, and enables long packets (>20 bytes), but requires more flash memory to use.

• CircuitPython Core: 200KB
• User Filesystem: 96KB
• Private Config Data: 28KB (which may get combined for 96+28=124KB total)

/*
    GNU linker script for NRF52 w/ s132 5.0.0 SoftDevice

    MEMORY MAP
    ------------------------------------------------------------------------
    START ADDR  END ADDR   SIZE    DESCRIPTION
    ----------  ---------- ------- -----------------------------------------
    0x00074000..0x00080000 ( 48KB) Serial + OTA Bootloader
    0x0006D000..0x00073FFF ( 28KB) Private Config Data (Bonding, Keys, etc.)
    0x00055000..0x0006CFFF ( 96KB) User Filesystem
    0x00023000..0x00054FFF (200KB) Application Code
    0x00001000..0x00022FFF (136KB) SoftDevice
    0x00000000..0x00000FFF   (4KB) Master Boot Record
*/

[tannewt]

This is done. Its in master and has other issues for its additional polish.