docs/system: arm: Add stm32 boards description

This adds the target guide for Netduino 2, Netduino Plus 2 and STM32VLDISCOVERY.

Signed-off-by: Alexandre Iooss <erdnaxe@crans.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210617165647.2575955-4-erdnaxe@crans.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

MAINTAINERS

@@ -898,6 +898,7 @@ M: Alexandre Iooss <erdnaxe@crans.org>
 L: qemu-arm@nongnu.org
 S: Maintained
 F: hw/arm/stm32vldiscovery.c
+F: docs/system/arm/stm32.rst
 
 Versatile Express
 M: Peter Maydell <peter.maydell@linaro.org>

docs/system/arm/stm32.rst

+STMicroelectronics STM32 boards (``netduino2``, ``netduinoplus2``, ``stm32vldiscovery``)
+========================================================================================
+
+The `STM32`_ chips are a family of 32-bit ARM-based microcontroller by
+STMicroelectronics.
+
+.. _STM32: https://www.st.com/en/microcontrollers-microprocessors/stm32-32-bit-arm-cortex-mcus.html
+
+The STM32F1 series is based on ARM Cortex-M3 core. The following machines are
+based on this chip :
+
+- ``stm32vldiscovery``  STM32VLDISCOVERY board with STM32F100RBT6 microcontroller
+
+The STM32F2 series is based on ARM Cortex-M3 core. The following machines are
+based on this chip :
+
+- ``netduino2``         Netduino 2 board with STM32F205RFT6 microcontroller
+
+The STM32F4 series is based on ARM Cortex-M4F core. This series is pin-to-pin
+compatible with STM32F2 series. The following machines are based on this chip :
+
+- ``netduinoplus2``     Netduino Plus 2 board with STM32F405RGT6 microcontroller
+
+There are many other STM32 series that are currently not supported by QEMU.
+
+Supported devices
+-----------------
+
+ * ARM Cortex-M3, Cortex M4F
+ * Analog to Digital Converter (ADC)
+ * EXTI interrupt
+ * Serial ports (USART)
+ * SPI controller
+ * System configuration (SYSCFG)
+ * Timer controller (TIMER)
+
+Missing devices
+---------------
+
+ * Camera interface (DCMI)
+ * Controller Area Network (CAN)
+ * Cycle Redundancy Check (CRC) calculation unit
+ * Digital to Analog Converter (DAC)
+ * DMA controller
+ * Ethernet controller
+ * Flash Interface Unit
+ * GPIO controller
+ * I2C controller
+ * Inter-Integrated Sound (I2S) controller
+ * Power supply configuration (PWR)
+ * Random Number Generator (RNG)
+ * Real-Time Clock (RTC) controller
+ * Reset and Clock Controller (RCC)
+ * Secure Digital Input/Output (SDIO) interface
+ * USB OTG
+ * Watchdog controller (IWDG, WWDG)
+
+Boot options
+------------
+
+The STM32 machines can be started using the ``-kernel`` option to load a
+firmware. Example:
+
+.. code-block:: bash
+
+  $ qemu-system-arm -M stm32vldiscovery -kernel firmware.bin

docs/system/target-arm.rst

@@ -97,6 +97,7 @@ undocumented; you can get a complete list by running
    arm/collie
    arm/sx1
    arm/stellaris
+   arm/stm32
    arm/virt
    arm/xlnx-versal-virt