Embedded Programming with ARM Cortex-M3 Basic Experiments 1 Alan Xiao, Ph.D Handheld Scientific, Inc. qiwei@handheldsci.com
Today s Topics Basics (with the Discovery board): 1. General Input/Output (GPIO) 2. USART (serial) 3. SysTick 4. Unique ID 5. EXTI - External Interrupt 6. Real-time Clock/Calendar 7. Timer/PWM 8. Watchdogs (independent/window) 9. CRC (Cyclic Redundancy Check) 10. PVD (Programmable Voltage Detector) 11. Sleep/Stop/Standby Modes Advanced (with the STM3210C or similar board): 1. I2C/EEPROM 2. ADC 3. RS-485 4. LCD display/touch Screen 5. SPI and Sensors 6. I2S Audio 7. Wireless (with external 315M and 2.4G modules) 8. USB Mouse and Keyboard 9. USB DFU (device firmware upgrade) 10. USB HID 11. USB Virtual COM Port 12. USB PCM Audio 13. Ethernet Telnet 14. Ethernet HTTP (i.e., control hardware via a web browser!) 15. Ethernet TFTP 16. USB Host 17. Running an OS on Cortex-M3 Copyright 2011 (c), Alan Xiao 2
Getting USART/Serial Port to work It is essential to get the USART to work. This is the conduit to the outside world. Most code examples will use the USART to display the results/messages. See code example on the intro session on how to get USART to work. Copyright 2011 (c), Alan Xiao 3
TTL/RS232 Level Consideration The USART IO in Discovery board is TTL level. To communicate with a PC: If you would like to use the RS-232 serial port (9 or 25pin D connector) on your PC (assuming there is one), you need a TTL to RS-232 level convertor such as a UT232R-200 from FTDI or a MAX3232 chip. If you would like to use an USB port, you need an USB to USART bridge such as an UB232R module from FTDI. In either case, only 3 wires are needed: Ground, RX<->TX, TX<-> RX. Copyright 2011 (c), Alan Xiao 4
Discovery and FTDI UB232R on a Bread Board Copyright 2011 (c), Alan Xiao 5
STM32 Memory Map 32-bit address: 4G addressable space. Everything has an address: registers, Flash, SRAM, etc. Flash starts at 0x08000000. SRAM starts at 0x20000000. That is probably all we need to know at the moment. Copyright 2011 (c), Alan Xiao 6
STM32 Boot Modes STM32 can boot from one of the following: User Flash Memory, System Memory and Embedded SRAM. This is controlled by two pins: System memory has a built-in serial boot loader for burning firmware into the chip without restoring to JTAG/SWD port. Booting and running program from RAM is faster. On the Discovery, both BOOT1 and BOOT2 are fixed to 0 so it only boots from user flash memory (although you can remove the soldered connectors to change that). Copyright 2011 (c), Alan Xiao 7
IAR Linker Memory Setting Copyright 2011 (c), Alan Xiao 8
SysTick Timer 24-bit countdown timer. It generates an interrupt when reaching zero and reloads value. The Library greatly simplifies its use. Simply call the following function: SysTick_Config(number_of_clock_cycles_in_a_period) Parameter can t exceeds 2^24 (about 16M). So for a 24M clock, the longest period is 16/24=667ms. If you need more control, mess up with the registers directly: Control & Status Register (enable, clock source, etc.). Reload value Current value Code example: simply print out a message in interrupt. Copyright 2011 (c), Alan Xiao 9
Unique Device ID Each STM32 device has a 96-bit (12 bytes) unique ID (guaranteed to be unique among the device family). Useful for: product serial number Security key for encryptions, for instance. To activate secure boot processer, etc. ID can be read as byte, half-word or word. Located in 0x1FFFF7E8 ~ 0x1FFFF7F3 memory location. See code example how to get it. Copyright 2011 (c), Alan Xiao 10
Interrupt Priority Two priorities: Preemptive Priority and Sub-priority. Lower number has higher priority. STM32 uses 4 bits in a register to specify the two priority settings. To be more flexible, it allows to specify the number of bits in that 4 bits for preemptive priority (the rest is for sub-priority). Group 0: 0 bit for preemptive priority. 4 bits for sub-priority. Group 1: 1 bit for preemptive priority. 3 bits for sub-priority. Group 4: 4 bits for preemptive priority. No bits for subpriority. Use NVIC_PriorityGroupConfig(NVIC_PriorityGroup_N) (n=0, 1, 2, 3 or 4) for the setting. Copyright 2011 (c), Alan Xiao 11
External Interrupts (EXTI) There are 16 EXTI lines: PA0, PB0,, PF0 use the same line EXTI_Line0 PA1, PB1,, PF1 use the same line EXTI_Line1 PA15, PB15,, PF15 use the same line EXTI_Line15 Use GPIO_EXTILineConfig() to tell the MCU which pin is being used. Copyright 2011 (c), Alan Xiao 12
External Interrupts (EXTI) EXTI Line 0 4 have their own dedicate interrupt source. EXTI Line 5-9 share one interrupt source, so do EXTI Line 10-15. Handler Names: EXTI0_IRQHandler();, EXTI4_IRQHandler() EXTI9_5_IRQHandler(); EXTI15_10_IRQHandler() To set up EXTI: Setup GPIO. Turn on AFIO (alternate function) Setup EXTI Source Setup EXTI Line Setup Interrupt Populate Interrupt handler Much better than polling. No debouncing is necessary! Copyright 2011 (c), Alan Xiao 13
External Interrupts (EXTI) For EXTI line 5-15, in the interrupt handler, need to have some code to determine which line generated the interrupt. Something like this: void EXTI9_5_IRQHandler(void) { if (EXTI_GetITStatus(EXTI_Line5)!= RESET) { EXTI_ClearITPendingBit(EXTI_Line5); } else if (EXTI_GetITStatus(EXTI_Line6)!= RESET) { EXTI_ClearITPendingBit(EXTI_Line6); } } Copyright 2011 (c), Alan Xiao 14
Power Modes Run Normal operation. Sleep Core stopped. Peripherals kept running Stop all clocks are stopped Standby all powered off except backup domain (backup registers and RTC). Copyright 2011 (c), Alan Xiao 15
Power Saving Modes Copyright 2011 (c), Alan Xiao 16
Power Saving Modes Power consumption in different power modes (very rough numbers): Normal (run): from a few ma to 50 ma (depending largely on the peripherals and clock speed) Sleep: from a few ma to 30mA Stop: 20 200uA Standby: a few ua Backup domain and RTC (on VBAT pin): 2uA. A good power-saving strategy is to put the MCU in stop/standby mode and wake it up periodically using RTC or external trigger. Copyright 2011 (c), Alan Xiao 17
Power Saving Modes Use the following Library calls to enter different power modes: PWR_EnterSTOPMode(PWR_Regulator_LowPow er, PWR_STOPEntry_WFE); PWR_EnterSTANDBYMode(); Stop mode: external interrupt can wake it up. Standby mode: only the wakeup pin (and reset) can wake it up. See code example. Copyright 2011 (c), Alan Xiao 18
Real-time Clock (RTC) Backup domain: RTC and 42 backup registers. Their power is provided by a dedicated pin (VBAT) which is usually connected to a battery (not in the Discovery board though). The backup domain is not affected by system reset (i.e., the RTC keeps running even during reset. The backup register values also survive resets). The RTC is driven by a dedicate clock, either internally or more often, an external 32.768K crystal. After reset, the access to the backup domain is prohibited until it is explicitly enabled, to prevent accidental writing. RTC can generate second interrupts or alarm interrupts. Copyright 2011 (c), Alan Xiao 19
What s Next Basics (with the Discovery board): 1. General Input/Output (GPIO) 2. USART (serial) 3. SysTick 4. Unique ID 5. EXTI - External Interrupt 6. Real-time Clock/Calendar 7. Timer/PWM 8. Watchdogs (independent/window) 9. CRC (Cyclic Redundancy Check) 10. PVD (Programmable Voltage Detector) 11. Sleep/Stop/Standby Modes Advanced (with the STM3210C or similar board): 1. I2C/EEPROM 2. ADC 3. RS-485 4. LCD display/touch Screen 5. SPI and Sensors 6. I2S Audio 7. Wireless (with external 315M and 2.4G modules) 8. USB Mouse and Keyboard 9. USB DFU (device firmware upgrade) 10. USB HID 11. USB Virtual COM Port 12. USB PCM Audio 13. Ethernet Telnet 14. Ethernet HTTP (i.e., control hardware via a web browser!) 15. Ethernet TFTP 16. USB Host 17. Running an OS on Cortex-M3 Copyright 2011 (c), Alan Xiao 20