STM32F4xx series micros are far more advanced than anything else similar in the market. Apart from being fast 32-bit MCUs, STM32F4s have rich hardware peripheral support with DSP engine bonus. In terms of capabilities versus price tag, STM32F4s are all-square-winners. In recent times there’s a surge in the STM32 user community. STM32 Discovery boards are proliferating like never before. In several occasions recently, I received tangible amounts of queries from readers regarding integration of STM32F4xx Standard Peripheral Library (SPL) with MikroC Pro for ARM and so even though it is not one of my mainstream posts on STM32 ARMs, I felt that I should address this topic. Previously I showed how to port STM32F1xx SPL for STM32F1xx series devices with MikroC. This post will not be different from the former one – only minute changes. I suggest readers to read the earlier post first before reading this one.
Tag Archives: STMicroelectronics
Everything related to digital electronics is related to time. Timer, counter, frequency, pulse width, clock and time are the most common words one may find in this arena. Microcontrollers just like humans need heart-beats and these come from clock sources. Apart from system clock, timers are clock sources that can be used as heart-beats for various applications. All modern micros are embedded with timer-counter modules and generally they are used for generating time bases, counting pulses, measuring time periods of waveforms, generating pulse width modulation (PWM) signals, triggering external devices and timing special events. STM32 micros have several timers designed for such applications. However unlike most 8-bit micros which possess two/three timers with limited functionalities, the timers of STM32s are very elaborate and complex. This explains why documentations related to timer modules take about 25% of any STM32 reference manual.
Before we begin exploring STM32 timers, I must point out that I won’t be able to cover every aspect of all timer modules as they are vast and need lot of explanations, something which is beyond the scope of a single post. This is why in this issue we shall explore the very basics of timer modules enough to get STM32 timers to work.
I remember that once in the beginning I said that I don’t want to buy a programmer/debugger hardware for learning a new MCU like the STM32 and also STM32s already come with built-in bootloader to facilitate programming via USART just like Arduino. Still the second is true. Well what about the first? To my own surprise I actually acquired a number of STM32-related stuffs since the time I started playing and exploring them. I actually bought both ST-Link 1 and 2 programmer-debuggers and several STM32 boards from Waveshare Electronics (http://www.wvshare.com). I believe learning new stuffs is more valuable than anything else.
ST-Link 1 (AKA ST-Link) and ST-Link v2 are both basically the same programmer/debugger hardware with some minor exceptions. ST-Link 2 has 5V tolerance for JTAG interface, it has a bicolour status LED and it also has a separate programming interface for STM8 micros unlike ST-Link 1. There is also an ISOL version of ST-Link2 that galvanically isolates it from its target using optoelectronics.
STM32 micros as we know are high-end micros and this high-end tag is not only due to its memory, speed and hardware richness. An advanced micro like this also needs advanced internal supporting hardware. Most of us know about watchdog timers from previous experiences with common 8 bit MCUs like AVR and PIC. However when it comes to STM32 the idea of watchdog circuitry is elaborated. The options available for clock are also enhanced in the STM32 micros. In this post, we will see some of these supporting internal hardware. We will examine the use and operation of two different watchdog timers – Independent Watchdog (IWDG) and Window Watchdog (WWDG), and the clock options usually found in common STM32 micros.
In a robust microcontroller like the STM32 there are several options for clock. At first the whole stuff may look a bit complex. Indeed it is complicated but not too difficult to understand. The simplified block diagram below shows the common clock arrangement inside a STM32F103 series MCU.
In my earlier post on STM32 GPIOs I showed how to flash a LED with variable delay times. That example was based on polling method where the code continuously monitored the logic state of a GPIO input pin attached to a push button to determine the delay amount. Obviously that won’t be an efficient technique when a program will be of a considerable size and complexity. This is simply so because the CPU will have to check the GPIO’s logic state every time the super-loop (while (1) loop in the main function) repeats and the push button will also not be responsive during the software delay function calls. Thus the overall performance is poor and not real-time. To get rid of these issues, we’ll need to use external interrupts – a vital feature in every common microcontroller.
STM32F1xx series are ARM Cortex M3 based MCUs. The Cortex M3 based MCUs have a sophisticated and yet easy to use interrupt system called the Nested Vectored Interrupt Controller (NVIC). It ensures low latency and high performance. There are several features of the NVIC and these are handled by the compiler. Our job is simply to enjoy the lightning fast interrupt responses owing to the NVIC. In many MCUs’ interrupt system, interrupt priority can be set and Reset has the highest interrupt priority over anything else. The same things go for STM32s too. However at present I’m not going to go that deep as that’s not needed for now. In some upcoming post may be I’ll discuss the NVIC in details. As per STM32’s reference manuals for more information on exceptions and NVIC programming read Chapter 5 Exceptions and Chapter 8 Nested Vectored Interrupt Controller of the ARM Cortex-M3 Technical Reference Manual. There are other interrupts that are related to RTC, timer, etc. We won’t also look into them in this post. We will learn about them when we learn about the related hardware with them.