More than 70% of silicon is ARM-based for it's customized sets energy efficient designs. These are categorized as ARM Cortex A, R and M.
These are high speed processors commonly found in smart phones and single-board computers. Some common examples are:
- Samsung Galaxy Note 10: ARM Cortex A76 & ARM Cortex A55
- Raspberry Pi: ARM Cortex A72
- Beaglebone Black: ARM Cortex A8
- Zynq Ultrascale+: ARM Cortex A53
These are rugged series used in safety-critical applications particularly industrial automation and automotive industry. Some common examples are:
- TI Hercules RM48: ARM Cortex R4F
- Zynq Ultrascale+: ARM Cortex R5
These are energy efficient microcontrollers used in general-purpose embedded systems as sensor nodes, ad-hoc communication and gateways etc. Some examples of these microcontrollers are:
- STM32F429ZI: Arm Cortex M4F
- TI Tiva TM4C12: ARM Cortex M4F
- EMF32 Gecko: ARM Cortex M3
- nRF52840: ARM Cortex M4
Development for embedded system engineers has never been about coming up with pieces but an end-to-end solution. For this purpose, all the parties at stake need to be considered and referred to throughout the development phase. One mode of communication with entities at each layer is documentation which is already well-versed for famous microcontrollers. In case of an embedded system design with STM32F4 microcontroller, following documentations need to be frequently referred to:
- STM32F429ZI Discovery Kit User Manual (UM1670).
- STM32F4xxxx Application Developer Reference Manual (RM0090).
- ARMv7-M Architecture Reference Manual. Moreover, well-versed coders consider referring to documentation around IDE as well:
- IAR C/C++ Devlopment Guide for ARM Microprocessor Family
The available peripherals on kit and their mappings on board are observed from STM32F429ZI Discovery Kit User Manual. Then the relevant peripheral is implemented through STM32F4xxxx Application Developer Reference Manual, while sometimes referring to ARMv7-M Architecture Reference Manual for core-specific features (as Nested Vector Interrupt Controller.)
Support for STM32F4 series microcontrollers is available in IDEs as following:
- GCC
- Keil MDK
- IAR Embedded We choose IAR Embedded Workbench for development in these labs.
Follow the IAR Embedded Workbench tutorial guide with this lab and program blink.c in microcontroller. Familiarize yourself with the debugging environment and try to understand the code as well.
Refer to blink.c for code.
- Line 18: Enable clock for GPIO port G in AHB1 Enable Register\footnote{Refer to section \texttt{6.3.12} of RM0090 reference manual for RCC AHB1 peripheral clock enable (RCC_AHB1ENR) register mappings.}. Clock is not provided to all peripherals by default for enabling energy efficiency. Hence clock needs to be enabled for each module in use.
- Line 21 ,22: Configure pins 13 & 14 as general purpose output pins in GPIO Mode Enable Register.
- Line 25, 26: Set pins 13 & 14 in Pull-up configuration through Push Pull Data Register. Other configurations can be Pull Down or Open Drain.
- Line 29: Set pin 13 high in Output Data Register.
- Line 33: Delay routine is defined in \texttt{line 39} which loops over the argument doing nothing ass \emph{NOP} assembly primitive.
- Line 34: Toggle LEDs using XOR operation.
Program button.c in microcontroller. Familiarize yourself with the debugging environment and try to understand the code as well.
Refer to file button.c for code.
- Line 18: Enable clock for GPIO port G and GPIO port A in AHB1 Enable Register.
- Line 46: Check port A from Input Data Register if input is high at pin 0. Then toggle the LED; otherwise do not.
Program exti.c in microcontroller. Familiarize yourself with the debugging environment and try to understand the code as well.
Refer to exti.c for code.
- Line 43: Enable system configuration clock in RCC APB2 peripheral clock enable register\footnote{Refer to section \texttt{6.3.18} of RM0090 reference manual for RCC APB2 peripheral clock enable (RCC_APB2ENR) register mappings.}.
- Line 46: Select source input for external interrupt as pin 0 of GPIO port A in system configuration controller external interrupt configuration register\footnote{Refer to section \texttt{8.2.4} of RM0090 reference manual.}.
- Line 47: Enable trigger type in Rising Trigger Selection Register\footnote{Refer to section \texttt{10.3.3} of RM0090 reference manual.}.
- Line 48: Set interrupt mask register\footnote{Refer to section \texttt{10.3.1} of RM0090 reference manual.} for EXTI0.
- Line 51: Set priority of interrupt request in Interrupt Priority Register\footnote{Refer to section \texttt{B3.4.9} of ARMv7-M Architecture Reference Manual}. \item \texttt{Line 54}: Using interrupt set enable register\footnote{Refer to section \texttt{B3.4.4} of ARMv7-M Architecture Reference Manual} to enable EXI interrupt requests. _ Line 18: Check if interrupt is from pin A0 from interrupt pending register\footnote{Refer to section \texttt{10.3.6} of RM0090 reference manual.}.
- Line 19: Clear interrupt in interrupt pending register.
Program tim2.c in microcontroller. Familiarize yourself with the debugging environment and try to understand the code as well.
Refer to tim2.c for code.
- Line 62: Enable clock for timer 2 in RCC APB1 peripheral clock enable register\footnote{Refer to section \texttt{6.3.24} in RM0090 for RCC_APB1ENR register mappings.}.
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Line 65 & 66: Calibrate timer 2 event update frequency using clock prescalar and autorelaod values. A generic formula in this regard being:
$$TIMx_EVT_f = \frac{CLK_{INT}}{(PSC+1)\times(ARR+1)}$$ * PLL clock \footnote{Refer to section \texttt{6.2} of RM0090 reference manual for a detailed discussion around clocks.} input frequency is configured in RCC PLL configuration register \footnote{Refer to section \texttt{6.3.2} of RM0090 reference manual RCC_PLLCFGR register mappings.}. Which for default values of register formulates to$84 Mhz$ . * Since PLL generated clock is used as system clock, the default internal clock is$84 MHz$ . \item Timer 2 prescalar value\footnote{Refer to section \texttt{15.4.11} in RM0090 for TIMx_PSC register mappings.} is 8399 hence the timer clock becomesTIM2_CLK_f = CLK_INT / (PSC+1) = 84 M / (8399+1) = 10 kHz* Event is generated after overflow of reaching the value of Auto-Reload Register\footnote{Refer to section \texttt{15.4.12} in RM0090 for TIMx_ARR register mappings.}. Setting it's value to 10,000, the frequency of event becomes:
TIM2_EVT_f = TIM2_f / (ARR+1) = 10000 / (10000+1) = 1 Hz
- Line 69: Updates interrupt enable after every iteration of interrupt generation in timer DMA/interrupt update enable register\footnote{Refer to section \texttt{15.4.4} in RM0090 for TIMx_DIER register mappings.} (TIMx_DIER).
- Line 72: Enable timer 2 module in timer 2 control register 1\footnote{Refer to section \texttt{15.4.1} in RM0090 for TIMx_CR1 register mappings.} (TIMx_CR1);
- Line 19: Clear timer 2 update interrupt flag (UIF) that interrupt should not trigger twice, exibiting false positives. The UIF bit is cleared in timer status register\footnote{Refer to section \texttt{15.4.5} in RM0090 for TIMx_SR register mappings.} (TIMx_SR).
Design a stopwatch representing time passed on seven segment display. The clock should initiate as button is pressed and return to 0 after 59 seconds. As button is pressed next time, the watch should stop. Subsequent button press will represent minutes passed. Next button press will result in reset of stopwatch and the one after it initiates it again.
Some use cases are elaborated as follows:
- (button pressed) 0, 1, 2, 3, 4, (button pressed) 4, (button pressed) 0, (button pressed) 0, (button pressed) 0, 1, 2, 3 ...
- (button pressed) 0, 1, 2, 3, 4, 5, 6, 7, 8, ... 59, 0, 1, 2, 3, 4, 5, 6, 9, ... 59, 0, 1, 2, 3, 4, (button pressed) 4, (button pressed) 2 (button pressed) 0, (button pressed) 1, 2, 3 ...
- ... (8 minutes passed) 0, 1, (button pressed) 1, (button pressed) 8 ...
- ... (87 minutes passed) 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, (button pressed) 16, (button pressed) 87, (button pressed) 0 ...