|A minimum build PianoForte - under test with a STM32F103CB|
In the last few days I have built up a couple of PianoForte boards in order to experiment with the hardware, write some code and generally rationalise the design.
The first board was fitted with a STM32F373 - which is an ARM Cortex M4 microcontroller with floating point unit, and the triple 16-bit ADCs. However, in order to write code for this, I had to fire up the CooCox COIDE - which is fairly hardcore programming, without the help of the familiar Arduino language, programming environment and libraries.
So in order to progress, the next pcb was fitted with a STM32F103CB. This is a Cortex M3 mcu with 256K of Flash and 48K of RAM. It also has the added anvantage in that it can be programmed using the Arduino_STM32, which is an extended version of the Arduino IDE. It's ADCs are only 12 bit - but that's still 4 times the resolution of the Arduino.
Details of Arduino_STM32 and links to Roger Clark's Github repository can be found here
When Arduino.cc introduced the Due, they had to extend the IDE to include the GCC compiler tools for ARM (as the Due uses an Atmel M3 ARM). They created a programming framework that would allow the incorporation of other ARM based boards into the Arduino ecosystem.
So now the range of STM32F103 microcontrollers, can be programme using the Arduino IDE - which opens these ARM processors up to a whole new generation of programmers.
There are several options available to us to get code into the STM32 chip on PianoForte. In this post I will deal initially with the most basic.
ARM microcontrollers come from the chip manufacturer with a preloaded bootloader. This can be programmed via a serial UART connection, using either proprietary or open source loader tools. The open source tool used by Arduino_STM32 is called STM32flash.
To use it, you first have to put the ARM into serial bootloader mode. This is done using a dedicated line on the processor called "Boot0". In the photograph above, the left hand side push switch is connected so that it pulls Boot0 high when pressed. Provided that Boot0 is high when the processor is released from reset (releasing the right hand switch), it will enter serial bootloader mode. It then communicates with the STM32flash program, and the code is loaded in a few seconds.
To use the serial bootoader, you need to have access to the USART1 Tx and Rx pins - and more specifically access them through ports PA9 and PA10. On PianoForte, PA9 and PA10 have been brought out to a FTDI programming header, which is the connector at the bottom left with the FTDI cable plugged in.
This is the simplest means of programming ARM devices, but you will need a USB to Serial programming cable or adaptor pcb - but these are now available very cheaply, and are very handy for debugging other projects.
The ARM mcu may also be programmed over USB - using a program/technique called Device Firmware Upgrade or Dfu. This will be covered in a later post.
Additionally you can load a program to the ARM using the STlink - which is proprietary programming/debug connection, which uses a couple of pins on the processor for clocked serial data transfer. For this you will need a ST Link programmer - but these are supplied on every STM Nucleo board - an mbed compatible dev board for about £10. I have included a dedicated ST Link header on PianoForte for this purpose. It's the located at the top left of the pcb.
Powering the PianoForte
PianoForte has a fairly flexible powering scheme based on the following options.
1. Plug it into the GPIO header of a Raspberry Pi - where it will pick up +5V and 0V from the Pi.
2. Plug a powered USB cable into the miniB USB connector. The PianoForte will run off the USB 5V supply. This can be from a PC or just a USB power supply.- plugged into the FTDI header.
3. From a FTDI cable or similar USB to serial adaptor
4. A 3.7V Lithium polymer cell - such as the 18650CA
5. Via a dc source (0.6V to 5V max) on the Vin pin of the power header
6. From two alkaline AAA cells plugged into a Keystone battery holder underneath the pcb.
The next post will cover the board features and running some test sketches on PianoForte, loaded from the Arduino_STM32 programming IDE.