We were using an AVR based Arduino to use this device, but since
the port is not merged, the microbit is the easiest board to use
with Zephyr.
Note the microbit doesn't have a such LED, this is simply a proof
of concept.

How to test:

- Apply this patch on zephyr-v2.3.0

  diff --git a/boards/arm/qemu_cortex_m0/qemu_cortex_m0.dts b/boards/arm/qemu_cortex_m0/qemu_cortex_m0.dts
  index a1b3044275..61b39506b1 100644
  --- a/boards/arm/qemu_cortex_m0/qemu_cortex_m0.dts
  +++ b/boards/arm/qemu_cortex_m0/qemu_cortex_m0.dts
  @@ -21,6 +21,18 @@
                  zephyr,flash = &flash0;
                  zephyr,code-partition = &slot0_partition;
          };
  +
  +       leds {
  +               compatible = "gpio-leds";
  +               led0: led_0 {
  +                       gpios = <&gpio0 21 GPIO_ACTIVE_LOW>;
  +                       label = "Green LED 0";
  +               };
  +       };
  +
  +       aliases {
  +               led0 = &led0;
  +       };
   };

   &gpiote {

- Build Zephyr blinky:

  $ west build -b qemu_cortex_m0 samples/basic/blinky

- Run QEMU

  $ qemu-system-arm -M microbit -trace led\* \
      -kernel ~/zephyrproject/zephyr/build/zephyr/zephyr.elf -trace led\*
  2953@1591704866.319665:led_set led name:'Green LED #0' state 0 -> 0
  2953@1591704867.329143:led_set led name:'Green LED #0' state 0 -> 1
  2953@1591704868.332590:led_set led name:'Green LED #0' state 1 -> 0

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/arm/microbit.c | 3 +++
 hw/arm/Kconfig    | 1 +
 2 files changed, 4 insertions(+)

diff --git a/hw/arm/microbit.c b/hw/arm/microbit.c
index ef213695bd..102661b66a 100644
--- a/hw/arm/microbit.c
+++ b/hw/arm/microbit.c
@@ -18,6 +18,7 @@
 #include "hw/arm/nrf51_soc.h"
 #include "hw/i2c/microbit_i2c.h"
 #include "hw/qdev-properties.h"
+#include "hw/misc/led.h"
 
 typedef struct {
     MachineState parent;
@@ -58,6 +59,8 @@ static void microbit_init(MachineState *machine)
     memory_region_add_subregion_overlap(&s->nrf51.container, NRF51_TWI_BASE,
                                         mr, -1);
 
+    create_led_by_gpio_id(OBJECT(machine), DEVICE(soc), 21, "Green LED #0");
+
     armv7m_load_kernel(ARM_CPU(first_cpu), machine->kernel_filename,
                        NRF51_SOC(soc)->flash_size);
 }
diff --git a/hw/arm/Kconfig b/hw/arm/Kconfig
index 9afa6eee79..2afaa7c8e9 100644
--- a/hw/arm/Kconfig
+++ b/hw/arm/Kconfig
@@ -436,6 +436,7 @@ config FSL_IMX6UL
 config MICROBIT
     bool
     select NRF51_SOC
+    select LED
 
 config NRF51_SOC
     bool
-- 
2.21.3

On Fri, 12 Jun 2020 at 18:54, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> We were using an AVR based Arduino to use this device, but since
> the port is not merged, the microbit is the easiest board to use
> with Zephyr.
> Note the microbit doesn't have a such LED, this is simply a proof
> of concept.

I know this is an RFC patchset, but just for the record, I
don't think we should add things to the board that the
real hardware doesn't have. (The microbit does have a 5x5
LED "display" but I dunno if this would be the best way
to implement that...)

thanks
-- PMM

On 6/15/20 6:02 PM, Peter Maydell wrote:
> On Fri, 12 Jun 2020 at 18:54, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>>
>> We were using an AVR based Arduino to use this device, but since
>> the port is not merged, the microbit is the easiest board to use
>> with Zephyr.
>> Note the microbit doesn't have a such LED, this is simply a proof
>> of concept.
> 
> I know this is an RFC patchset, but just for the record, I
> don't think we should add things to the board that the
> real hardware doesn't have. (The microbit does have a 5x5
> LED "display" but I dunno if this would be the best way
> to implement that...)

Yes, I plan to implement a generic LED array matrix and
use it in the microbit (and few other boards).

Without the AVR port merged, the microbit is the quickest
way for me to test with Zephyr.

> 
> thanks
> -- PMM
>