RASPBERRYPI: Add support for RP2040 MCU

[facchinm]

Summary of changes

This PR introduces a new target, RaspberryPi's RP2040 microcontroller.
The technical specifications are:

• Dual core cortex-m0+ @ 120 Mhz
• 264KB RAM
• External flash with XIP

Impact of changes

Supported features:

ANALOGIN
FLASH
I2C
I2CSLAVE
INTERRUPTIN
PWMOUT"
SERIAL
SERIAL_FC
SPI
USTICKER
WATCHDOG
USBDEVICE
RESET_REASON

Not yet supported:

RTC
LPTICKER
PIO (an IP specific for the chip, which require some extra tooling to be properly supported)

Migration actions required

Documentation

This porting is based on https://github.com/raspberrypi/pico-sdk with minimal patches applied (should make it easier to update to new releases)
https://datasheets.raspberrypi.org/rp2040/rp2040-datasheet.pdf

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Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

Will be provided soon

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

@pennam @0xc0170

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[ciarmcom]

@facchinm, thank you for your changes.
@0xc0170 @ARMmbed/mbed-os-maintainers please review.

[WestfW]

Should the link step be using "--specs=nano.specs" as well as "--specs=nosys.specs" ? My reading indicates that they do work together, and an experiment with just that change appears to work, and cuts ~20k off the binary size.

[0xc0170]

Should the link step be using "--specs=nano.specs" as well as "--specs=nosys.specs" ? My reading indicates that they do work together, and an experiment with just that change appears to work, and cuts ~20k off the binary size.

nano lib is selected if C standard lib is set to small. nosys.specs are default linker option. This board can support small standard lib.

[noonfom]

Are you going to add FEATURE_BLE to the NANO_RP2040_CONNECT's JSON description?

[WestfW]

None of the various APIs (PWM, Serial, I2C, SPI) return the pins to GPIO mode when they are turned off. (actually, I don't see ANY code to turn off I2C or SPI.)
See https://forum.arduino.cc/t/digitalwrite-does-not-work-after-analogwrite-on-rp2040-boards/
I guess theoretically, this should be done in digitalWrite() and digitalRead() for compatibility with older boards (where that would automatically turn off PWM, for example), but that might cause problems for MBED.
It should at least be done in pinMode() and the _free() functions that exist.

[mergify]

This PR cannot be merged due to conflicts. Please rebase to resolve them.

[0xc0170]

Should this pull request still be opened?

[Arvind-Srinivasan]

So is there a plan to merge this PR in? What is left to get this target added in?

[0xc0170]

@facchinm I am closing this pull request, the best would be to open a new one with up to date information.

[willianpaixao]

@facchinm what's left to implement? If it's just a git conflict case I can fix them.

[facchinm]

@willianpaixao There should be nothing left to implement but tests are not passing due to some cmake incompatibilities with the way we use to ignore some sdk folders.

[willianpaixao]

@facchinm could you write more about those problems? I could try to tackle them, but need some context.

[facchinm]

@pennam do you still have some logs of the compliance test failures?

[pennam]

After applying this patch i recovered from my working directory:

diff --git a/targets/targets.json b/targets/targets.json
index 6985f4346f..879558d676 100644
--- a/targets/targets.json
+++ b/targets/targets.json
@@ -8363,7 +8363,12 @@
     },
     "RP2040": {
         "inherits": ["Target"],
+        "mbed_rom_start": "0x10000000",
+        "mbed_rom_size": "0x1000000",
+        "mbed_ram_start": "0x20000000",
+        "mbed_ram_size": "0x42000",
         "components_add": ["FLASHIAP"],
+        "device_name": "RP2040",
         "core": "Cortex-M0+",
         "supported_toolchains": ["GCC_ARM"],
         "extra_labels": [
@@ -8396,6 +8401,7 @@
     },
     "NANO_RP2040_CONNECT": {
         "inherits": ["RP2040"],
+        "bootloader_supported": true,
         "macros_add": [
             "PICO_RP2040_USB_DEVICE_ENUMERATION_FIX=1",
             "PICO_NO_BINARY_INFO=1",

Running mbed test gives this output:
test.log

[multiplemonomials]

Just wanted to provide an update, @JohnK1987 and I are now working on an updated version of this PR for the Mbed Community Edition project (linked above). Currently it is able to build and work for basic projects, though some Mbed tests are still not passing.