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
- Quadrature Encoder
- SDCard support
- SPI NOR Flash
- Nokia 5110 LCD Display support
- 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 two versions of very similar boards: One is red and one is
blue. See http://www.stm32duino.com/viewtopic.php?f=28&t=117

The Red Board:

Good things about the red board:

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

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.

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

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.
- User LED on PC13
- 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 * to me 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
succesfully, 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 configs/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.

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

The nsh configuration has been used to test the Quadrture 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_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 configs/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_FS_WRITABLE=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 (Philips 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] []

[ dd free mb sh 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

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)

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 configs subdirectory and
hence, the board that supports the particular chip or SoC.

CONFIG_ARCH_BOARD=stm32f103-minium

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

CONFIG_ARCH_CALIBRATION - Enables some build in instrumentation that
cause a 100 second delay during boot-up. This 100 second delay
serves no purpose other than it allows you to calibratre
CONFIG_ARCH_LOOPSPERMSEC. You simply use a stop watch to measure
the 100 second delay then adjust CONFIG_ARCH_LOOPSPERMSEC until
the delay actually is 100 seconds.

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_CAN1_BAUD - CAN1 BAUD rate. Required if CONFIG_STM32_CAN1 is defined.
CONFIG_CAN2_BAUD - CAN1 BAUD rate. Required if CONFIG_STM32_CAN2 is defined.
CONFIG_CAN_TSEG1 - The number of CAN time quanta in segment 1. Default: 6
CONFIG_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_SPI_DMA - Use DMA to improve SPI 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:

cd tools
./configure.sh STM32F103 Minimum/
cd -

Where 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 CodeSourcery 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_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery 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 SYLOG 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 loggin device (UART2 in this
configuraion):

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.