README
======

This README discusses issues unique to NuttX configurations for the
STM32F103C8T6 Minimum System Development Board for ARM Microcontroller.

Contents
========

  - STM32F103C8T6 Minimum System Development Boards:
  - LEDs
  - UARTs
  - Timer Inputs/Outputs
  - Using 128KiB of Flash instead of 64KiB
  - Nintendo Wii Nunchuck
  - Quadrature Encoder
  - SDCard support
  - SPI NOR Flash
  - Nokia 5110 LCD Display support
  - HYT271 sensor
  - DS18B20 sensor
  - USB Console support
  - STM32F103 Minimum - specific Configuration Options
  - Configurations

STM32F103C8T6 Minimum System Development Boards:
================================================

  This STM32F103C8T6 minimum system development board is available from
  several vendors on the net, and may be sold under different names or
  no name at all. It is based on a STM32F103C8T6 and has a DIP-40 form-
  factor.

  There are four versions of very similar boards: Red, Blue, RoboDyn Black and
  Black.
  See: https://wiki.stm32duino.com/index.php?title=Blue_Pill
  https://wiki.stm32duino.com/index.php?title=Red_Pill
  https://wiki.stm32duino.com/index.php?title=RobotDyn_Black_Pill
  https://wiki.stm32duino.com/index.php?title=Black_Pill

  The Red Board:

    Good things about the red board:

    - 1.5k pull up resistor on the PA12 pin (USB D+) which you can
      programmatically drag down for automated USB reset.
    - large power capacitors and LDO power.
    - User LED on PC13

    Problems with the red board:

    - Silk screen is barely readable, the text is chopped off on some of
      the pins
    - USB connector only has two anchor points and it is directly soldered
      on the surface
    - Small reset button with hardly any resistance

  The Blue Board:

    Good things about the blue board:

    - Four soldered anchor point on the USB connector. What you can't tell
      from this picture is that there is a notch in the PCB board and the USB
      connector sits down inside it some. This provides some lateral stability
      that takes some of the stress off the solder points.
    - It has nice clear readable silkscreen printing.
    - It also a larger reset button.
    - User LED on PC13

    Problems with the blue board:

    - Probably won't work as a USB device if it has a 10k pull-up on PA12. You
      have to check the pull up on PA12 (USB D+). If it has a 10k pull-up
      resistor, you will need to replace it with a 1.5k one to use the native
      USB.
    - Puny voltage regulator probably 100mA.

    A schematic for the blue board is available here:
    http://www.stm32duino.com/download/file.php?id=276

  The Black Board:

    - User LED is on PB12.
    - Mounting holes.

  Both Boards:

    Nice features common to both:

    - SWD pins broken out and easily connected (VCC, GND, SWDIO, SWCLK)
    - USB 5V is broken out with easy access.
    - Power LED
    - You can probably use more flash (128k) than officially documented for
      the chip (stm32f103c8t6 64k), I was able to load 115k of flash on mine
      and it seemed to work.

    Problems with both boards:

    - No preloaded bootloader (this isn't really a problem as the
      entire 64k of flash is available for use)
    - No user button

  This is the board pinout based on its form-factor for the Blue board:

        USB
        ___
  -----/ _ \-----
  |B12       GND|
  |B13       GND|
  |B14      3.3V|
  |B15       RST|
  |A8        B11|
  |A9        B10|
  |A10        B1|
  |A11        B0|
  |A12        A7|
  |A15        A6|
  |B3         A5|
  |B4         A4|
  |B5         A3|
  |B6         A2|
  |B7         A1|
  |B8         A0|
  |B9        C15|
  |5V        C14|
  |GND       C13|
  |3.3V       VB|
  |_____________|

LEDs
====

  The STM32F103 Minimum board has only one software controllable LED.
  This LED can be used by the board port when CONFIG_ARCH_LEDS option is
  enabled.

  If enabled the LED is simply turned on when the board boots
  successfully, and is blinking on panic / assertion failed.

UARTs
=====

  UART/USART PINS
  ---------------

  USART1
    RX      PA10
    TX      PA9
  USART2
    CK      PA4
    CTS     PA0
    RTS     PA1
    RX      PA3
    TX      PA2
  USART3
    CK      PB12
    CTS     PB13
    RTS     PB14
    RX      PB11
    TX      PB10

Default USART/UART Configuration
--------------------------------

  USART1 (RX & TX only) is available through pins PA9 (TX) and PA10 (RX).

Timer Inputs/Outputs
====================

  TIM1
    CH1     PA8
    CH2     PA9*
    CH3     PA10*
    CH4     PA11*
  TIM2
    CH1     PA0*, PA15, PA5
    CH2     PA1, PB3
    CH3     PA2, PB10*
    CH4     PA3, PB11
  TIM3
    CH1     PA6, PB4
    CH2     PA7, PB5*
    CH3     PB0
    CH4     PB1*
  TIM4
    CH1     PB6*
    CH2     PB7
    CH3     PB8
    CH4     PB9*

 * Indicates pins that have other on-board functions and should be used only
   with care (See board datasheet).

Using 128KiB of Flash instead of 64KiB
======================================

  Some people figured out that the STM32F103C8T6 has 128KiB of internal memory
  instead of 64KiB as documented in the datasheet and reported by its internal
  register.

  In order to enable 128KiB you need modify the linker script to reflect this
  new size. Open the boards/arm/stm32/stm32f103-minimum/scripts/ld.script and replace:

    flash (rx) : ORIGIN = 0x08000000, LENGTH = 64K

  with

    flash (rx) : ORIGIN = 0x08000000, LENGTH = 128K

  Enable many NuttX features (ie. many filesystems and applications) to get a
  large binary image with more than 64K.

  We will use OpenOCD to write the firmware in the STM32F103C8T6 Flash. Use a
  up to dated OpenOCD version (ie. openocd-0.9).

  You will need to create a copy of original openocd/scripts/target/stm32f1x.cfg
  to openocd/scripts/target/stm32f103c8t6.cfg and edit the later file replacing:

    flash bank $_FLASHNAME stm32f1x 0x08000000 0 0 0 $_TARGETNAME

  with

    flash bank $_FLASHNAME stm32f1x 0x08000000 0x20000 0 0 $_TARGETNAME

  We will use OpenOCD with STLink-V2 programmer, but it will work with other
  programmers (JLink, Versaloon, or some based on FTDI FT232, etc).

  Open a terminal and execute:

    $ sudo openocd -f interface/stlink-v2.cfg -f target/stm32f103c8t6.cfg

  Now in other terminal execute:

    $ telnet localhost 4444

    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    Open On-Chip Debugger

    > reset halt
    stm32f1x.cpu: target state: halted
    target halted due to debug-request, current mode: Thread
    xPSR: 0x01000000 pc: 0x080003ac msp: 0x20000d78

    > flash write_image erase nuttx.bin 0x08000000
    auto erase enabled
    device id = 0x20036410
    ignoring flash probed value, using configured bank size
    flash size = 128kbytes
    stm32f1x.cpu: target state: halted
    target halted due to breakpoint, current mode: Thread
    xPSR: 0x61000000 pc: 0x2000003a msp: 0x20000d78
    wrote 92160 bytes from file nuttx.bin in 4.942194s (18.211 KiB/s)

    > reset run
    > exit

  Now NuttX should start normally.

Nintendo Wii Nunchuck:
======================

  There is a driver on NuttX to support Nintendo Wii Nunchuck Joystick. If you
  want to use it please select these options:

  - Enable the I2C1 at System Type -> STM32 Peripheral Support, it will enable:

    CONFIG_STM32_I2C1=y

  - Enable to Custom board/driver initialization at RTOS Features -> RTOS hooks

    CONFIG_BOARD_LATE_INITIALIZE=y

  - Enable the I2C Driver Support at Device Drivers, it will enable this symbol:

    CONFIG_I2C=y

  - Nintendo Wii Nunchuck Joystick at Device Drivers -> [*] Input Device Support

    CONFIG_INPUT=y
      CONFIG_INPUT_NUNCHUCK=y

  - Enable the Nunchuck joystick example at Application Configuration -> Examples

  CONFIG_EXAMPLES_NUNCHUCK=y
    CONFIG_EXAMPLES_NUNCHUCK_DEVNAME="/dev/nunchuck0"

  You need to connect GND and +3.3V pins from Nunchuck connector to GND and 3.3V
  of stm32f103-minimum respectively (Nunchuck also can work connected to 5V, but
  I don't recommend it). Connect I2C Clock from Nunchuck to SCK (PB6) and the
  I2C Data to SDA (PB7).

Quadrature Encoder:
===================

  The nsh configuration has been used to test the Quadrature Encoder
  (QEncoder, QE) with the following modifications to the configuration
  file:

  - These setting enable support for the common QEncode upper half driver:

   CONFIG_SENSORS=y
     CONFIG_SENSORS_QENCODER=y

  - This is a board setting that selected timer 4 for use with the
    quadrature encode:

    CONFIG_STM32F103MINIMUM_QETIMER=4

  - These settings enable the STM32 Quadrature encoder on timer 4:

    CONFIG_STM32_TIM4_CAP=y
    CONFIG_STM32_TIM4_QE=y
    CONFIG_STM32_TIM4_QECLKOUT=2800000
    CONFIG_STM32_QENCODER_FILTER=y
    CONFIG_STM32_QENCODER_SAMPLE_EVENT_6=y
    CONFIG_STM32_QENCODER_SAMPLE_FDTS_4=y

  - These settings enable the test case at apps/examples/qencoder:

    CONFIG_EXAMPLES_QENCODER=y
    CONFIG_EXAMPLES_QENCODER_DELAY=100
    CONFIG_EXAMPLES_QENCODER_DEVPATH="/dev/qe0"

  In this configuration, the QEncoder inputs will be on the TIM4 inputs of
  PB6 and PB7.

SPI NOR Flash support:
======================

  We can use an extern SPI NOR Flash with STM32F103-Minimum board. In this case
  we tested the Winboard W25Q32FV (32Mbit = 4MiB).

  You can connect the W25Q32FV module in the STM32F103 Minimum board this way:
  connect PA5 (SPI1 CLK) to CLK; PA7 (SPI1 MOSI) to DI; PA6 (SPI MISO) to DO;
  PA4 to /CS; Also connect 3.3V to VCC and GND to GND.

  You can start with default "stm32f103-minimum/nsh" configuration option and
  enable/disable these options using "make menuconfig" :

  System Type  --->
      STM32 Peripheral Support  --->
          [*] SPI1

  Board Selection  --->
      [*] MTD driver for external 4Mbyte W25Q32FV FLASH on SPI1
      (0)   Minor number for the FLASH /dev/smart entry
      [*]   Enable partition support on FLASH
      (1024,1024,1024,1024) Flash partition size list

  RTOS Features  --->
      Stack and heap information  --->
              (512) Idle thread stack size
              (1024) Main thread stack size
              (256) Minimum pthread stack size
              (1024) Default pthread stack size

  Device Drivers  --->
      -*- Memory Technology Device (MTD) Support  --->
              [*]   Support MTD partitions
              -*-   SPI-based W25 FLASH
              (0)     W25 SPI Mode
              (20000000) W25 SPI Frequency

  File Systems  --->
      [ ] Disable pseudo-filesystem operations
      -*- SMART file system
      (0xff) FLASH erased state
      (16)  Maximum file name length

  Memory Management  --->
      [*] Small memory model

  Also change the boards/arm/stm32/stm32f103-minimum/scripts/ld.script file to use 128KB
  of Flash instead 64KB (since this board has a hidden 64KB flash) :

  MEMORY
  {
      flash (rx) : ORIGIN = 0x08000000, LENGTH = 128K
      sram (rwx) : ORIGIN = 0x20000000, LENGTH = 20K
  }

  Then after compiling and flashing the file nuttx.bin you can format and mount
  the flash this way:

  nsh> mksmartfs /dev/smart0p0
  nsh> mksmartfs /dev/smart0p1
  nsh> mksmartfs /dev/smart0p2
  nsh> mksmartfs /dev/smart0p3

  nsh> mount -t smartfs /dev/smart0p0 /mnt
  nsh> ls /mnt
  /mnt:

  nsh> echo "Testing" > /mnt/file.txt

  nsh> ls /mnt
  /mnt:
   file.txt

  nsh> cat /mnt/file.txt
  Testing

  nsh>

SDCard support:
===============

  Only STM32F103xx High-density devices has SDIO controller. STM32F103C8T6 is a
  Medium-density device, but we can use SDCard over SPI.

  You can do that enabling these options:

    CONFIG_FS_FAT=y

    CONFIG_MMCSD=y
    CONFIG_MMCSD_NSLOTS=1
    CONFIG_MMCSD_SPI=y
    CONFIG_MMCSD_SPICLOCK=20000000
    CONFIG_MMCSD_SPIMODE=0

    CONFIG_STM32_SPI=y
    CONFIG_STM32_SPI1=y

    CONFIG_SPI=y
    CONFIG_SPI_CALLBACK=y
    CONFIG_SPI_EXCHANGE=y

  And connect a SDCard/SPI board on SPI1. Connect the CS pin to PA4, SCK to
  PA5, MOSI to PA7 and MISO to PA6. Note: some chinese boards use MOSO instead
  of MISO.

Nokia 5110 LCD Display support:
===============================

  You can connect a low cost Nokia 5110 LCD display in the STM32F103 Minimum
  board this way: connect PA5 (SPI1 CLK) to CLK; PA7 (SPI1 MOSI) to DIN; PA4
  to CE; PA3 to RST; PA2 to DC. Also connect 3.3V to VCC and GND to GND.

  You can start with default "stm32f103-minimum/nsh" configuration option and
  enable these options using "make menuconfig" :

  System Type  --->
      STM32 Peripheral Support  --->
          [*] SPI1

  Device Drivers  --->
      -*- SPI Driver Support  --->
          [*]   SPI exchange
          [*]   SPI CMD/DATA

  Device Drivers  --->
      LCD Driver Support  --->
          [*] Graphic LCD Driver Support  --->
              [*]   Nokia 5110 LCD Display (Phillips PCD8544)
              (1)     Number of PCD8544 Devices
              (84)    PCD8544 X Resolution
              (48)    PCD8544 Y Resolution

  Graphics Support  --->
      [*] NX Graphics
      (1)   Number of Color Planes

      (0x0) Initial background color
          Supported Pixel Depths  --->
              [ ] Disable 1 BPP
      [*]   Packed MS First

      Font Selections  --->
          (7) Bits in Character Set
          [*] Mono 5x8

  Application Configuration  --->
      Examples  --->
          [*] NX graphics "Hello, World!" example
          (1)   Bits-Per-Pixel

  After compiling and flashing the nuttx.bin inside the board, reset it.
  You should see it:

  NuttShell (NSH)
  nsh> ?
  help usage:  help [-v] [<cmd>]

    [           dd          free        mb          source      usleep
    ?           echo        help        mh          sleep       xd
    cat         exec        hexdump     mw          test
    cd          exit        kill        pwd         true
    cp          false       ls          set         unset

  Builtin Apps:
    nxhello

  Now just run nxhello and you should see "Hello World" in the display:

  nsh> nxhello

HYT271 sensor support:
======================

The existing sensor configuration allows connecting several sensors of type
hyt271 on i2c bus number 2. For full feature support, be able to change the
i2c address of the sensor, the following hardware setup is necessary.

  ----------                                            -----------
  |        |------ GND ------------------------ GND ----|         |
  |        |                                            |         |
  |        |                                            |         |
  |        |                                            |         |
  |        |---- POWIN A00 ------.                      |         |
  |        |                     |                      |         |
  |        |                    4.7k                    |         |
  |        |                     |                      |         |
  | STM32  |--- POWOUT A01 ------.------.------ VDD ----| HYT271  |
  |        |                     |      |               |         |
  |        |                    2.2k    |               |         |
  |        |                     |      |               |         |
  |        |----- SDA2 B11 ------.----  | ----- SDA ----|         |
  |        |                            |               |         |
  |        |                           2.2k             |         |
  |        |                            |               |         |
  |        |----- SCL2 B10 -------------.------ SCL ----|         |
  |        |                                            |         |
  ---------                                             -----------

DS18B20 sensor support:
======================

The existing sensor configuration allows connecting several sensors of type
ds18b20 on 1wire bus number 2. The following hardware setup is necessary.

  ---------                                            -----------
  |       |------ GND ----------.------------- GND ----|         |
  |       |                                            |         |
  |       |                                            |         |
  |       |                                            |         |
  |       |------ VDD ----------.------------- VDD ----|         |
  | STM32 |                     |                      | DS18B20 |
  |       |                    4.7k                    |         |
  |       |                     |                      |         |
  |       |----- TX2 A02 -------.------.------- DQ ----|         |
  |       |                                            |         |
  --------                                             -----------

USB Console support:
====================

  The STM32F103C8 has a USB Device controller, then we can use NuttX support
  to USB Device. We can the console over USB enabling these options:

  System Type  --->
    STM32 Peripheral Support  --->
      [*] USB Device

  It will enable:  CONFIG_STM32_USB=y

  Board Selection  --->
    -*- Enable boardctl() interface
    [*]   Enable USB device controls

  It will enable: CONFIG_BOARDCTL_USBDEVCTRL=y

  Device Drivers  --->
    -*- USB Device Driver Support  --->
      [*]   USB Modem (CDC/ACM) support  --->

  It will enable:  CONFIG_CDCACM=y and many default options.

  Device Drivers  --->
    -*- USB Device Driver Support  --->
      [*]   USB Modem (CDC/ACM) support  --->
        [*]   CDC/ACM console device

  It will enable: CONFIG_CDCACM_CONSOLE=y

  Device Drivers  --->
    [*] Serial Driver Support  --->
      Serial console (No serial console)  --->
        (X) No serial console

  It will enable: CONFIG_NO_SERIAL_CONSOLE=y

  After flashing the firmware in the board, unplug and plug it in the computer
  and it will create a /dev/ttyACM0 device in the Linux. Use minicom with this
  device to get access to NuttX NSH console (press Enter three times to start)

MCP2515 External Module
=======================

  You can use an external MCP2515 (tested with NiRen MCP2515_CAN module) to
  get CAN Bus working on STM32F103C8 chip (remember the internal CAN cannot
  work with USB at same time because they share the SRAM buffer).

  You can connect the MCP2515 module in the STM32F103 Minimum board this way:
  connect PA5 (SPI1 CLK) to SCK; PA7 (SPI1 MOSI) to SI; PA6 (SPI MISO) to SO;
  PA4 to CS; B0 to INT. Also connect 5V to VCC and GND to GND.

  Note: Although MCP2515 can work with 2.7V-5.5V it is more stable when using
  it on BluePill board on 5V.

  Testing: you will need at least 2 boards each one with a MCP2515 module
  connected to it. Connect CAN High from the first module to the CAN High of
  the second module, and the CAN Low from the first module to the CAN Low of
  the second module.

  You need to modify the "CAN example" application on menuconfig and create
  two firmware versions: the first firmware will be Read-only and the second
  one Write-only. Flash the first firmware in the first board and the second
  firmware in the second board. Now you can start the both boards, run the
  "can" command in the Write-only board and then run the "can" command in the
  Read-only board. You should see the data coming.

STM32F103 Minimum - specific Configuration Options
==================================================

    CONFIG_ARCH - Identifies the arch/ subdirectory.  This should
       be set to:

       CONFIG_ARCH=arm

    CONFIG_ARCH_family - For use in C code:

       CONFIG_ARCH_ARM=y

    CONFIG_ARCH_architecture - For use in C code:

       CONFIG_ARCH_CORTEXM3=y

    CONFIG_ARCH_CHIP - Identifies the arch/*/chip subdirectory

       CONFIG_ARCH_CHIP=stm32

    CONFIG_ARCH_CHIP_name - For use in C code to identify the exact
       chip:

       CONFIG_ARCH_CHIP_STM32F103C8=y

    CONFIG_ARCH_BOARD_STM32_CUSTOM_CLOCKCONFIG - Enables special STM32 clock
       configuration features.

       CONFIG_ARCH_BOARD_STM32_CUSTOM_CLOCKCONFIG=n

    CONFIG_ARCH_BOARD - Identifies the boards/ subdirectory and
       hence, the board that supports the particular chip or SoC.

       CONFIG_ARCH_BOARD=stm32f103-minimum

    CONFIG_ARCH_BOARD_name - For use in C code

       CONFIG_ARCH_BOARD_STM32_MINIMUM=y

    CONFIG_ARCH_LOOPSPERMSEC - Must be calibrated for correct operation
       of delay loops

    CONFIG_ENDIAN_BIG - define if big endian (default is little
       endian)

    CONFIG_RAM_SIZE - Describes the installed DRAM (SRAM in this case):

       CONFIG_RAM_SIZE=20480 (20Kb)

    CONFIG_RAM_START - The start address of installed DRAM

       CONFIG_RAM_START=0x20000000

    CONFIG_ARCH_LEDS - Use LEDs to show state. Unique to boards that
       have LEDs

    CONFIG_ARCH_INTERRUPTSTACK - This architecture supports an interrupt
       stack. If defined, this symbol is the size of the interrupt
        stack in bytes.  If not defined, the user task stacks will be
      used during interrupt handling.

    CONFIG_ARCH_STACKDUMP - Do stack dumps after assertions

  Individual subsystems can be enabled:

    AHB
    ---
    CONFIG_STM32_CRC
    CONFIG_STM32_BKPSRAM

    APB1
    ----
    CONFIG_STM32_TIM2
    CONFIG_STM32_TIM3
    CONFIG_STM32_TIM4
    CONFIG_STM32_WWDG
    CONFIG_STM32_IWDG
    CONFIG_STM32_SPI2
    CONFIG_STM32_USART2
    CONFIG_STM32_USART3
    CONFIG_STM32_I2C1
    CONFIG_STM32_I2C2
    CONFIG_STM32_CAN1
    CONFIG_STM32_PWR -- Required for RTC

    APB2
    ----
    CONFIG_STM32_TIM1
    CONFIG_STM32_USART1
    CONFIG_STM32_ADC1
    CONFIG_STM32_ADC2
    CONFIG_STM32_SPI1

  Timer devices may be used for different purposes.  One special purpose is
  to generate modulated outputs for such things as motor control.  If CONFIG_STM32_TIMn
  is defined (as above) then the following may also be defined to indicate that
  the timer is intended to be used for pulsed output modulation or ADC conversion.
  Note that ADC require two definitions:  Not only do you have
  to assign the timer (n) for used by the ADC, but then you also have to
  configure which ADC (m) it is assigned to.

    CONFIG_STM32_TIMn_PWM   Reserve timer n for use by PWM, n=1,..,14
    CONFIG_STM32_TIMn_ADC   Reserve timer n for use by ADC, n=1,..,14
    CONFIG_STM32_TIMn_ADCm  Reserve timer n to trigger ADCm, n=1,..,14, m=1,..,3

  For each timer that is enabled for PWM usage, we need the following additional
  configuration settings:

    CONFIG_STM32_TIMx_CHANNEL - Specifies the timer output channel {1,..,4}

  NOTE: The STM32 timers are each capable of generating different signals on
  each of the four channels with different duty cycles.  That capability is
  not supported by this driver:  Only one output channel per timer.

  JTAG Enable settings (by default only SW-DP is enabled):

    CONFIG_STM32_JTAG_FULL_ENABLE - Enables full SWJ (JTAG-DP + SW-DP)
    CONFIG_STM32_JTAG_NOJNTRST_ENABLE - Enables full SWJ (JTAG-DP + SW-DP)
      but without JNTRST.
    CONFIG_STM32_JTAG_SW_ENABLE - Set JTAG-DP disabled and SW-DP enabled

  STM32F103 Minimum specific device driver settings

    CONFIG_U[S]ARTn_SERIAL_CONSOLE - selects the USARTn (n=1,2,3)
       for the console and ttys0 (default is the USART1).
    CONFIG_U[S]ARTn_RXBUFSIZE - Characters are buffered as received.
       This specific the size of the receive buffer
    CONFIG_U[S]ARTn_TXBUFSIZE - Characters are buffered before
       being sent.  This specific the size of the transmit buffer
    CONFIG_U[S]ARTn_BAUD - The configure BAUD of the UART.  Must be
    CONFIG_U[S]ARTn_BITS - The number of bits.  Must be either 7 or 8.
    CONFIG_U[S]ARTn_PARTIY - 0=no parity, 1=odd parity, 2=even parity
    CONFIG_U[S]ARTn_2STOP - Two stop bits

  STM32F103 Minimum CAN Configuration

    CONFIG_CAN - Enables CAN support (one or both of CONFIG_STM32_CAN1 or
      CONFIG_STM32_CAN2 must also be defined)
    CONFIG_CAN_EXTID - Enables support for the 29-bit extended ID.  Default
      Standard 11-bit IDs.
    CONFIG_CAN_FIFOSIZE - The size of the circular buffer of CAN messages.
      Default: 8
    CONFIG_CAN_NPENDINGRTR - The size of the list of pending RTR requests.
      Default: 4
    CONFIG_CAN_LOOPBACK - A CAN driver may or may not support a loopback
      mode for testing. The STM32 CAN driver does support loopback mode.
    CONFIG_STM32_CAN1_BAUD - CAN1 BAUD rate.  Required if CONFIG_STM32_CAN1
      is defined.
    CONFIG_STM32_CAN2_BAUD - CAN1 BAUD rate.  Required if CONFIG_STM32_CAN2
      is defined.
    CONFIG_STM32_CAN_TSEG1 - The number of CAN time quanta in segment 1.
      Default: 6
    CONFIG_STM32_CAN_TSEG2 - the number of CAN time quanta in segment 2.
      Default: 7
    CONFIG_STM32_CAN_REGDEBUG - If CONFIG_DEBUG_FEATURES is set, this will generate an
      dump of all CAN registers.

  STM32F103 Minimum SPI Configuration

    CONFIG_STM32_SPI_INTERRUPTS - Select to enable interrupt driven SPI
      support. Non-interrupt-driven, poll-waiting is recommended if the
      interrupt rate would be to high in the interrupt driven case.
    CONFIG_STM32_SPIx_DMA - Use DMA to improve SPIx transfer performance.
      Cannot be used with CONFIG_STM32_SPI_INTERRUPT.

Configurations
==============

  Instantiating Configurations
  ----------------------------
  Each STM32F103 Minimum configuration is maintained in a sub-directory and
  can be selected as follow:

    tools/configure.sh STM32F103 Minimum:<subdir>

  Where <subdir> is one of the following:

  Configuration Directories
  -------------------------
  nsh:
  ---
    Configures the NuttShell (nsh) located at apps/examples/nsh. This
    configuration enables a console on UART1. Support for
    builtin applications is enabled, but in the base configuration no
    builtin applications are selected.

  jlx12864g:
  ---------
    This is a config example to use the JLX12864G-086 LCD module. To use this
    LCD you need to connect PA5 (SPI1 CLK) to SCK; PA7 (SPI1 MOSI) to SDA; PA4
    to CS; PA3 to RST; PA2 to RS.

  nrf24:
  ---------
    This is a config example to test the nrf24 terminal example. You will need
    two stm32f103-minimum board each one with a nRF24L01 module connected this
    way: connect PB1 to nRF24 CE pin; PA4 to CSN; PA5 (SPI1 CLK) to SCK; PA7
    (SPI1 MOSI) to MOSI; PA6 (SPI1 MISO) to MISO; PA0 to IRQ.

  usbnsh:
  -------

    This is another NSH example.  If differs from other 'nsh' configurations
    in that this configurations uses a USB serial device for console I/O.

    NOTES:

    1. This configuration uses the mconf-based configuration tool.  To
       change this configuration using that tool, you should:

       a. Build and install the kconfig-mconf tool.  See nuttx/README.txt
          see additional README.txt files in the NuttX tools repository.

       b. Execute 'make menuconfig' in nuttx/ in order to start the
          reconfiguration process.

    2. By default, this configuration uses the ARM EABI toolchain
       for Windows and builds under Cygwin (or probably MSYS).  That
       can easily be reconfigured, of course.

       CONFIG_HOST_WINDOWS=y                   : Builds under Windows
       CONFIG_WINDOWS_CYGWIN=y                 : Using Cygwin
       CONFIG_ARM_TOOLCHAIN_GNU_EABI=y      : GNU EABI toolchain for Windows

    3. This configuration does have UART2 output enabled and set up as
       the system logging device:

       CONFIG_SYSLOG_CHAR=y               : Use a character device for system logging
       CONFIG_SYSLOG_DEVPATH="/dev/ttyS0" : UART2 will be /dev/ttyS0

       However, there is nothing to generate SYSLOG output in the default
       configuration so nothing should appear on UART2 unless you enable
       some debug output or enable the USB monitor.

    4. Enabling USB monitor SYSLOG output.  If tracing is enabled, the USB
       device will save encoded trace output in in-memory buffer; if the
       USB monitor is enabled, that trace buffer will be periodically
       emptied and dumped to the system logging device (UART2 in this
       configuration):

       CONFIG_USBDEV_TRACE=y                   : Enable USB trace feature
       CONFIG_USBDEV_TRACE_NRECORDS=128        : Buffer 128 records in memory
       CONFIG_NSH_USBDEV_TRACE=n               : No builtin tracing from NSH
       CONFIG_NSH_ARCHINIT=y                   : Automatically start the USB monitor
       CONFIG_USBMONITOR=y              : Enable the USB monitor daemon
       CONFIG_USBMONITOR_STACKSIZE=2048 : USB monitor daemon stack size
       CONFIG_USBMONITOR_PRIORITY=50    : USB monitor daemon priority
       CONFIG_USBMONITOR_INTERVAL=2     : Dump trace data every 2 seconds

       CONFIG_USBMONITOR_TRACEINIT=y    : Enable TRACE output
       CONFIG_USBMONITOR_TRACECLASS=y
       CONFIG_USBMONITOR_TRACETRANSFERS=y
       CONFIG_USBMONITOR_TRACECONTROLLER=y
       CONFIG_USBMONITOR_TRACEINTERRUPTS=y

    5. By default, this project assumes that you are *NOT* using the DFU
       bootloader.

    Using the Prolifics PL2303 Emulation
    ------------------------------------
    You could also use the non-standard PL2303 serial device instead of
    the standard CDC/ACM serial device by changing:

      CONFIG_CDCACM=y               : Disable the CDC/ACM serial device class
      CONFIG_CDCACM_CONSOLE=y       : The CDC/ACM serial device is NOT the console
      CONFIG_PL2303=y               : The Prolifics PL2303 emulation is enabled
      CONFIG_PL2303_CONSOLE=y       : The PL2303 serial device is the console

  veml6070:
  --------
    This is a config example to use the Vishay VEML6070 UV-A sensor. To use this
    sensor you need to connect PB6 (I2C1 CLK) to SCL; PB7 (I2C1 SDA) to SDA of
    sensor module. I used a GY-VEML6070 module to test this driver.
