boards/serpente: add serpente board

[benpicco]

Contribution description

The Serpente boards are low-cost development boards designed to be used with Adafruit’s CircuitPython.

Three versions of the board board exist, but they all the same except for the USB connector.
The standard Serpente board contains a female USB Type-C connector, the Serpente Plug C
contains a male USB Type-C connector, and the Serpente Plug uses the board itself as a Type-A USB plug.

The board comes with the UF2 bootloader that works very much like the arduino bootloader from #12304, but uses a different memory address & magic.

Testing procedure

Use BOARD=serpente with the make command.

Example with micropython application:

     make BOARD=serpente -C examples/micropython flash

RIOT will automatically trigger a reset to the bootloader, but this only works if RIOT is still running on the board.
If your application has crashed or got erased, make flash will not be able to trigger a bootloader reset.

To manually enter the bootloader, quickly press the Reset button twice.
You know you've successfully entered the bootloader when the LED begins flashing blue.

Sometimes flashing fails and the board gets stuck in the bootloader.
In this case, just run make flash again when the device is not busy anymore.

Issues/PRs references

requires #13652 for proper USB ID.

[fjmolinas]

@benpicco can you provide some test output?

[benpicco]

@benpicco can you provide some test output?

tests/periph_uart

I connected UART0 TX with UART1 RX and UART0 RX with UART1 TX

2020-04-26 20:26:01,282 # ================================
2020-04-26 20:26:01,284 # This application is intended for testing additional UART
2020-04-26 20:26:01,284 # 
2020-04-26 20:26:01,285 # Available devices:               2
> init 0 115200
2020-04-26 20:26:06,239 #  init 0 115200
2020-04-26 20:26:06,241 # Success: Initialized UART_DEV(0) at BAUD 115200
2020-04-26 20:26:06,491 # UARD_DEV(0): test uart_poweron() and uart_poweroff()  ->  [OK]
> ini1 1152000
2020-04-26 20:26:09,927 #  init 1 115200
2020-04-26 20:26:09,929 # Success: Initialized UART_DEV(1) at BAUD 115200
2020-04-26 20:26:10,179 # UARD_DEV(1): test uart_poweron() and uart_poweroff()  ->  [OK]
> send 0 Hello\ UART1
2020-04-26 20:26:21,703 #  send 0 Hello\ UART1
2020-04-26 20:26:21,704 # UART_DEV(0) TX: Hello UART1
2020-04-26 20:26:21,705 # Success: UART_DEV(1) RX: [Hello UART1]\n
> send 1 Hello\ UART0
2020-04-26 20:26:27,511 #  send 1 Hello\ UART0
2020-04-26 20:26:27,512 # UART_DEV(1) TX: Hello UART0
2020-04-26 20:26:27,514 # Success: UART_DEV(0) RX: [Hello UART0]\n

A patch was needed to fix tests/periph_uart for the non STDIO_UART_DEV case that will be in a separate PR (#13956).

tests/pkg_littlefs2

2020-04-26 20:44:08,474 # START
2020-04-26 20:44:08,476 # main(): This is RIOT! (Version: 2020.04-devel-1859-gd2fef8-serpente-r2)
2020-04-26 20:44:11,342 # ........
2020-04-26 20:44:11,342 # 8 tests)

tests/periph_spi

2020-04-26 20:55:03,154 # Refer to the README.md file for more information.
2020-04-26 20:55:03,155 # There are 2 SPI devices configured for your platform.
> init 1 0 0 0 7
2020-04-26 20:55:24,221 #  init 1 0 0 0 7
2020-04-26 20:55:24,223 # SPI_DEV(1) initialized: mode: 0, clk: 0, cs_port: 0, cs_pin: 7
> send abcd
2020-04-26 20:56:47,182 #  send abcd
2020-04-26 20:56:47,183 # Sent bytes
2020-04-26 20:56:47,183 #    0    1    2    3 
2020-04-26 20:56:47,184 #  0x61 0x62 0x63 0x64
2020-04-26 20:56:47,185 #    a    b    c    d 
2020-04-26 20:56:47,185 # Received bytes
2020-04-26 20:56:47,186 #    0    1    2    3 
2020-04-26 20:56:47,186 #  0x61 0x62 0x63 0x64
2020-04-26 20:56:47,187 #    a    b    c    d

i2c_scan

I connected a GY-85 module to the I2C bus

2020-04-26 21:07:29,081 #  i2c_scan 0
2020-04-26 21:07:29,082 # Scanning I2C device 0...
2020-04-26 21:07:29,084 # addr not ack'ed = "-", addr ack'ed = "X", addr reserved = "R", error = "E"
2020-04-26 21:07:29,085 # 0x00 R R R R R R R R R R R R R R - -
2020-04-26 21:07:29,087 # 0x10 - - - - - - - - - - - - - - - -
2020-04-26 21:07:29,088 # 0x20 - - - - - - - - - - - - - - - -
2020-04-26 21:07:29,089 # 0x30 - - - - - - - - - - - - - - - -
2020-04-26 21:07:29,090 # 0x40 - - - - - - - - - - - - - - - -
2020-04-26 21:07:29,092 # 0x50 - - - X - - - - - - - - - - - -
2020-04-26 21:07:29,094 # 0x60 - - - - - - - - X - - - - - - -
2020-04-26 21:07:29,095 # 0x70 - - - - - - - - R R R R R R R R

[fjmolinas]

Looks, good some nitpicks below.

Also when I generated the docs the image for the board is way to big, not sure how to re-size images in doxygen.

[benpicco]

I rebased because the MTD API now requires additional parmaters

[fjmolinas]

Only the doxygen image issue remains, I tried a couple of things but was not succesfull..

[benpicco]

This should fix it.

[fjmolinas]

Looks good now, please squash!

[benpicco]

squashed.

[fjmolinas]

ACK, code looks good and @benpicco provided some test output!

[benpicco]

Thank you for the review!