Sending data over SPI with the STM32 using polling is simple and reliable but your processor is blocked, unable to do anything else until the transfer is complete. Direct Memory Access (DMA) allows you to initiate a transfer of a block of data and then carry on doing something else…
The Nokia LCD displays are among my favourite toys. Generally, I use a monochrome display intended for the Nokia 3410 ‘phone. This a display size of 96 x 48 pixels and can display bitmaps as well as text in 6 rows of 16 characters. It is smaller than the more common 16×2 text-only displays, easier to drive, cheaper, uses fewer connections, much more flexible and is readily available. And now, I have connected one up to my STM32F103 Cortex-M3 processor. As a first go with the SPI peripheral on these processors, it has been quite instructive…
In general the dsPIC is well blessed with peripherals. The dsPIC30F6015 I am using at the moment has two serial ports in addition to a couple of SPI ports and an I2C port. These UARTs seem pretty easy to use as well. Still, like other peripherals on the dsPIC, they still found a way to catch me out. My own fault for not reading the data sheet properly. The trick here is to realise that there are FIFO buffers associated with the ports.
It was all getting too awkward. A bit of short sighted design on my part had the Nokia LCD sharing an SPI port with the motor encoders. This meant that I had to turn off the encoders to write to the LCD. While no motion information would be lost by doing this, it effectively meant that I could not, for example, have the mouse hold position while updating the display. In the end I took it all apart and patched the circuit board so that the LCD is now driven from the SPI1 port and the encoders are on the SPI2 port.
The LS7366 is a 32 bit counter with a direct interface for quadrature signals from incremental encoders. There is also an index channel for marker functions. The interface to the microcontroller is SPI mode 0 making it relatively easy to drive with a variety of common controllers. Decimus has one of these on each motor channel connected to the encoders on the back of the Faulhaber 2224 coreless motors. There is very little information about these chips available except the data sheet. This is how they are used on Decimus. (more…)
I use SPI on my micromouse both to talk to the Nokia graphical LCD and to talk to the LS7366 quadrature encoders. A large number of devices can be connected to the SPI data lines, MOSI and MISO. Each device needs its own select line. This all appear very simple and friendly. There is, however a potential problem due to the flexibility of the SPI configuration.
This is a fairly big jump. With the LEDs and buttons tested, it is time to add the main graphical display, made from a Nokia cellphone display. Also, there is the main system timer event.
The simple user IO is working, and it is time to add a system timer. This will generate an interrupt every millisecond. In the final mouse a lot of work will be done in here – processing buttons, driving the LEDs, reading sensors and calculating drive signals for the motors.While that may seem a lot in a millisecond, the dsPIC used in primus can execute about 16,000 instructions in that tme and we should only need a small proportion of that time. (more…)