Wireless Controller for Ultra Low Power Cc430 Based Transceiver

Transcription

1 Wireless Controller for Ultra Low Power Cc430 Based Transceiver K. Sasi Chandana 1, Mr.A.Naresh 2, Smt.S.Aruna 3 1 Student, ECE Department, Andhra University, Visakhapatnam, India 2 Scientist D, Instrumentation Department, NSTL, Visakhapatnam, India 3 Assistant Professor, ECE Department, Visakhapatnam, India Abstract Power Consumption is the main criteria now days in any embedded application. The less the power consumed the more the durability of the product. The main aim of the project is to establish a Ultra Low Power RF link between two CC430F6147 transceiver units, one Control Unit and the other Application Unit such that their power consumption is maintained at less than 1 micro amperes and thereby making the Application Unit durable for several years. Software implementation includes development of protocols for controlling CC430F6147 remotely and reduces power consumption such that total circuit works only on micro amperes current. The Control Unit controls the Application Unit by sending commands. This include developing Embedded software in Embedded C to establish Ultra Low Power wireless communication between Control and Application units using the Low Power modes of CC430F6147 Micro Controller. Keywords Low Power Mode, Wake on Radio, MSP430 Micro Controller. I. INTRODUCTION Wireless technologies have been available for decades. However, they tend to use significant amounts of power and need specialized equipment to establish communications. Some identified end products that may implement a low power radio system, include cell phones, health and fitness devices, home automation, heating, ventilating, and air conditioning, remote controls, gaming, human interface devices, smart meters, payment and many others. These applications are all constrained by the following critical key requirements: ultra low power, low cost and physical size. The less the power consumed the more will be the durability of the product. And less power consumption is very essential in certain applications like implanting a device in human body, so that the battery life of device will be more and thereby reducing the need of replacing the battery frequently by surgery. CC430F6147 is Ultra low power microcontroller with inbuilt Sub 1 GHz RF transceiver, making it suitable for battery powered, long endurance and compact embedded applications. Software implementation includes development of protocols for controlling CC430F6147 remotely and reduces power consumption such that total circuit works only on micro amperes current. II. MICRO CONTROLLER The microcontroller used for the application in this thesis is CC430F6147 (which is a MSP430 based Micro Controller) which is a mixed signal microcontroller which can process both analog as well as digital signal. It has advanced features like: True System-on-Chip (SoC) for Low-Power Wireless Communication Applications Wide Supply Voltage Range: 3.6 V Down to 1.8 V High performance Sub 1 GHz RF Transceiver Core The CC430F6147 is a microcontroller system-on-chip configurations combining the excellent performance of the state-of-the-art CC1101 sub-1-ghz RF transceiver with the MSP430 CPUXV2, up to 32 kb of in-system programmable flash memory, up to 4 kb of RAM, two 16-bit timers, a highperformance 10-bit A/D converter with eight external inputs plus internal temperature and battery sensors, comparator, universal serial communication interfaces (USCIs), 128-bit AES security accelerator, hardware multiplier, DMA, realtime clock module with alarm capabilities, LCD driver, and up to 44 I/O pins. A. Low power mode The Low Power mode feature is the major advantage of this Micro Controller which is useful in achieving the low power consumption. The CC430 is designed from the ground up for low power. This includes both design and process implementation. Despite this, the bulk of power savings is realized by placing the CC430 in various power saving modes. We first have to understand what consumes the most current in the CC430. This breaks down as follows: CC430 CPU draws the most, proportional to the frequency at which it is running. Clocks and Oscillators, especially high speed clocks. Modules and Peripherals Saving power comes down to shutting off as many modules, peripherals, and clocks as we can, for as long as possible without violating the application time requirements. It is also important to reduce the speed of the CPU as it can significantly affect power consumption. The issue isn't always what to turn off but when, and when to wake them up.to enable low power the CC430 supports several modes, each shutting off the CC430 more and more: Active Mode (AM) - Not a low power mode but rather the mode in which everything is turned on, except perhaps for some peripherals LPM0 - CPU and MCLK are shutoff. SMCLK and ACLK remain active. LPM1 - CPU and MCLK are off, as in LPM1, but DCO and DC generator are disabled if the DCO is not used for SMCLK. ACLK is active. LPM2 - CPU, MCLK, SMCLK and DCO are disabled, while DC generator is still enabled. ACLK is active. ISSN: Page 381

2 LPM3 - CPU, MCLK, SMCLK, DCO and DC generator are disabled. ACLK is active. LPM4 - CPU and all clocks disabled LPM3.5 and LMP4.5 are additional low-power modes in which the regulator of the PMM is completely disabled, providing additional power savings. Not all devices support all LPMx.5 modes.because there is no power supplied to VCORE during LPMx.5, the CPU and all digital modules including RAM are unpowered. This disables the entire device and, as a result, the contents of the registers and RAM are lost. Any essential values should be stored to flash prior to entering LPMx.5. These LPM modes refer to the individual bits in the Status Register. By setting and clearing the bits in the SR, one can turn off CPU and clocks resulting in certain Low Power Modes. Let's look at the power consumption profile of the various LPMs: Wake-on-radio functionality for automatic lowpower RX polling Separate 64-byte RX and TX data FIFOs (enables burst mode data transmission) The CC1101 has built-in hardware support for packet oriented radio protocols. In transmit mode, the packet handler can be configured to add the following elements to the packet stored in the TX FIFO: A programmable number of preamble bytes A two byte synchronization (sync) word. A CRC checksum computed over the data field C. Packet Format Fig 2. Packet format Fig 1.Power consumption profiles of various LPMs At 1MHz, we go from 300uA down to less than 1uA by switching to LPM3. This is what makes the CC430 such a good microcontroller for low power applications. It can survive for years on batteries. Low power modes allow us to conserve energy, but we do pay a penalty for using them. That penalty is the time it takes to go from a low power mode to Active Mode. The deeper we go into low power modes, the longer it takes to go to Active Mode. The primary reason is that oscillators take time to come to a stable state. B.CC1101 CC1101 is a low-cost sub-1 GHz transceiver designed for very low-power wireless applications. The circuit is mainly intended for the ISM (Industrial, Scientific and Medical) and SRD (Short Range Device) frequency bands at 315, 433, 868, and 915 MHz, but can easily be programmed for operation at other frequencies in the MHz, MHz and MHz bands. The RF transceiver is integrated with a highly configurable baseband modem. The modem supports various modulation formats and has a configurable data rate up to 600 kbps. Low-Power Features: 200 na sleep mode current consumption Fast startup time; 240 µs from sleep to RX or TX mode The format of the data packet can be configured and consists of the following items Preamble Synchronization word Length byte or constant programmable packet length Optional address byte Payload Optional 2 byte CRC The preamble pattern is an alternating sequence of ones and zeros ( ) the minimum length of the preamble is programmable. When enabling TX, the modulator will start transmitting the preamble. When the programmed number of preamble bytes has been transmitted, the modulator will send the sync word and then data from the TX FIFO if data is available. If the TX FIFO is empty, the modulator will continue to send preamble bytes until the first byte is written to the TX FIFO. The modulator will then send the sync word and then the data bytes. D. Active Modes CC1101 has two active modes: receive and transmit. These modes are activated directly by the MCU by using the SRX and STX command strobes, or automatically by Wake on Radio. The frequency synthesizer must be calibrated regularly. CC1101 has one manual calibration option (using the SCAL strobe), and three automatic calibration options, controlled by the MCSM0.FS_AUTOCAL setting: Calibrate when going from IDLE to either RX or TX (or FSTXON) Calibrate when going from either RX or TX to IDLE automatically Calibrate every fourth time when going from either RX or TX to IDLE automatically. ISSN: Page 382

3 E. Wake On Radio(WOR) The Wake-On-Radio (WOR) feature of the CC430 is a recommended method for conserving power in wireless systems in which the radio periodically wakes up from SLEEP mode and listens for incoming packets. The Wake-On-Radio (WOR) functionality enables the radio to periodically wake up from SLEEP mode and listen for incoming packets with minimal CPU interaction. The WOR feature on the CC430 family devices provides two events, Event 0 and Event 1, which can be leveraged to wake up and stabilize the radio core oscillator, and to change the radio to RX mode. Another programmable parameter that the WOR feature uses is the RX timeout, which determines the period during which the radio stays in RX mode. If a packet is received before the period reaches the RX timeout value, the CC430 can process the received packet and return to SLEEP mode. On the other hand, if no packet is received during the RX active period, the radio resumes the SLEEP state after the RX timeout. used to identify either an RX timeout or the reception of an incoming packet, respectively. Following the LNA_PD or RX_EOP interrupt, the radio can be returned to the SLEEP state. The WOR program 1. After setting up the RF1A core for standard RF operation, the main program configures the WOR control registers and enables WOR_EVENT0 interrupt before going into low power mode (LPMx). 2. Upon the EVENT0 interrupt, the program enters the interrupt handler RF1A_ISR where an SRX command strobe is issued to transition the RF1A core from SLEEP state to IDLE and subsequently RX state. 3. The unreliability of RF1A registers during the RF1A core state transition from sleep to active, while the radio oscillator is stabilizing before being switched to source the RF1A core. This stabilization might take up to 810 µs, during which any access to the RF1A register might fail. Therefore, after a Fig.3. WOR Event 0 and Event 1 Figure 3 shows the relationship between the WOR events and the different radio states. The application has the flexibility to specify the wake up interval (t Event0 ) as well as the RX active period (t RX timeout ) within each interval. RF systems that require power optimization could lengthen the wake up interval or decrease the RX active duty cycle. Vice versa, more responsive systems with higher packet reception rates could be obtained by decreasing t Event0 or increasing t RX timeout values. The WOR Timer feature on the CC430 is implemented slightly different from the previous implementation in the CC1101. The WOR functionality in CC1101 allows the chip to transition between states (WOR, SLEEP, RX, receive packet) without any CPU intervention. In the CC430 family devices, the WOR Timer feature provides the similar vehicle for the radio to replicate that RF operation flow, but it requires the CPU to manage the transitions between the radio states directly. Specifically, after the RF1A is configured in WOR mode, Event 0 can be configured as an interrupt for the CPU core to initiate the RF1A state change from SLEEP to RX mode. Additionally, the Low Noise Amplifier Power Down (LNA_PD) or RX End of Packet (RX_EOP) events can be Wake-up strobe to the RF1A core from, the CPU must stay active for 810 µs to ensure the RF oscillator is stabilized before accessing the radio registers. 4. Once RF1A is in RX mode, the Low Noise Amplifier Power down (LNA_PD) and RX End of Packet (RX_EOP) interrupts are enabled. CPU returns to sleep mode and waits for one of these two events. 5. In case of a packet reception, CPU enters RF1A_ISR to disable the interrupts, returns to active mode to process the packet, and strobes RF1A core to enter the SLEEP state again with the SWOR command. 6. If no packet is received, after the programmed time, RX will time out and signal the LNA_PD interrupt. In the LNA_PD ISR, the MSP430 strobes SWOR over the RF1A interface to enter the SLEEP state and wait for the next EVENT0. Detailed description of the three RF modes: RX Mode Device stays in RX mode and CPU stays in LPM3. RF1A_ISR is configured to handle RF packet reception. Green LED toggles to indicate packet reception. TX Mode ISSN: Page 383

4 Device stays in TX mode and periodically transmits an RF packet every 100 ms. WOR Mode Device enters WOR mode and CPU goes to LPM3, proceeds through the program flow, in each cycle with the period t EVENT0 = 1.06 s, t RX Timeout = 1.96 ms. For the user to operate in a comfortable manner the Application unit will have switches. The switches are programmed in such a way that the user can easily control the pulse amplitudes, pulse width and pulse rates and he can also set up the maximum and minimum threshold levels of the parameters. III. APPLICATION For the pulse stimulation in medical application such as continuous stimulation at prescribed amplitude & pulse rate at disease affected organs there is a need to have Ultra low power wireless communication between transmitting unit & controlling circuit. This system need to stimulate data with variable parameters of the receiver from the transmitter through RF communication. The system provides long battery life for the RF communication devices. This can be used in ultra low power and battery powered applications especially in medical and consumer applications where frequent interactions between transmitter and receiver are required. The circuit is intended to work in the ISM (Industrial Scientific Medical) band as it is well suited for the medical applications. Mainly for the medical field where portability is the major concern the devices should be provided with long battery life. In order to have long life of battery there is a necessity to have ultra low power communication between the transmitter and receiver. The ultra low power communication can be achieved by developing the software code in order to effectively use the low power features of devices selected for the design of the system.the main objective of this thesis is to design and development the embedded software to establish ultra low power wireless communication between Application unit and Control unit and also optimization of the power consumption during the transmission and reception. This Thesis consists of design and development of embedded software for 1. Application unit 2. Control unit Fig.4 interfacing of two RF modules The above block diagram here explains two RF modules each consisting of Ultra low power CC430F6147 interfaced through a wireless RF link. The figure 4 shows the establishment of low power wireless communication between control unit and active unit The transmitter (controlling unit) controls the receiver by sending proper commands by using switches such that the parameters of the application unit are changed accordingly. This Ultra low power communication between transmitting unit & controlling circuits can be used mainly in many medical applications where doctor need to control the pulses of the patient, and in controlling large machines from some distance where a person cannot reach the machine for those it is not possible to change the battery of the device frequently. Attaining ultra low power consumption of the devices is major aspect for achieving long battery life. The Application unit and Control unit consists of Texas Instruments ultra low power MSP430F169 microcontroller and ultra low power RF communication chip CC1101, which best suites medical applications and with few passive components. In this, microcontroller is interacted with transceiver CC1101 internally. PC is connected to Microcontroller through JTAG with MSP-FET430 debugger. Wireless Controlling Device is interfaced with pulse generator. Signal transmission between Control unit & interfaced unit is through chip antenna, which has frequency range MHz CRO Applicatio n unit Power source Debugger Handheld unit In this work, the proposed Programming language used in development of Application Unit for brain stimulator is Embedded C program. The programming is done in IAR embedded Workbench. Fig.5 Practical test bench setup to implement the communication between control unit and application unit ISSN: Page 384

5 A. Programming Application and Control Units Micro controller initializes the CC1101 by filling its configuration registers for required settings. Here dummy data from CC1101 is ignored.cc1101 is initialized in wake on radio and interrupt mode, where interrupt is generated on its GDO pins. After CC1101 initialization, DACs and ADCs are initialized for data simulation and feedback measurement, battery voltage monitoring. Timer A is initialized in interrupt mode so as to generate interrupt for every 50µs.This time is used for controlling the parameters of simulated data. The CC1101 is inbuilt in microcontroller CC430F6147 through SCLK, SI, SO & CSn (Chip select) pins of SPI. CC1101 is programmed using the write register function to use all features of it mainly wake on radio which enables CC1101 to periodically wake up from SLEEP and listen for incoming packets without MCU interaction. The configuration of CC1101 is done by programming 8-bit register using the IAR workbench software. The registers are configured for GDOx output pin configurations, RX FIFO and TX FIFO thresholds, Sync word settings, Packet length and Packet automation control, Channel number, Frequency synthesizer control, Modem configurations, Main Radio Control State Machine configuration for CC1101 to operate in normal RX and in Wake on Radio mode, Bit Synchronization configuration, AGC control, Front end RX configuration, Front end TX configuration, RC oscillator configuration and various test settings for the proper function of CC1101 according to the application developed. CC1101 is programmed for write into a register and read from register. The transmitting unit is programmed by initializing CC1101 and commands are written for switch controls. Each command starts with $ and ends with # and command data is five Bytes for identifying different commands. In the Controlling section the received command generates interrupt, which wakes up the micro controller from low power mode. The command will be processed and decoded. Based on the command data simulation will be varied for various parameters. The total program is implemented in low power mode. The programming is done for two programmers i.e. for DAC0 and DAC1. The control unit can control the parameters of the application unit for both the DACs independently. In order to program how to write into a register of CC1101 first the address in which the required value is filling is need to sent to the transmit buffer, and then the flag should be cleared. Now the value is sent to it. Again the flag is cleared. Thus the value is stored in its particular register address. To read the values in the registers the program is developed by making the CSn pin low in order to make the slave (CC1101) ready. Now the address is sent and waited until the transmission is complete. The flag is cleared and dummy variable is write in to that address in order to read from the register and waited until the reception of the value completed. The flag is cleared and CSn pin is disabled. The DAC10 module is a 10-bit, voltage output digital-toanalog converter.dac10 control and data registers are programmed with ON TIME and OFF TIME values in order to generate Pulses of required amplitude. The ADC module is a high-performance 10-bit analog-todigital converter.adc10 control registers are programmed to set the reference voltage for the pulse generated by DAC. In this thesis internal 2.5V reference is used. The watchdog timer is a 16-bit timer that can be used as a watchdog or as an interval timer. The primary function of t it is to perform a controlled system restart after a software problem occurs. If the selected time interval expires, a system reset is generated. If the watchdog function is not needed in an application, the module can be configured as an interval timer and can generate interrupts at selected time intervals. When the watchdog timer is not required, the WDTHOLD bit can be used to hold the WDTCNT, reducing power consumption. B. Low Power Programming The CC430F6147 controller is programmed by using the low power mode and WOR features. Here the LMP4 is used; means CPU and all clocks are disabled. So the power consumption is reduced when in low power mode 4 up micro Amperes. And also as using Wake On Radio, the CC1101 will not always in RX mode. It will periodically come into RX mode and rest time will be in Sleep mode, where the current consumed will be in nano Amperes. Thus in sleep mode the power consumption will be less. And when in Rx mode power is consumed up to milli Amperes. So we can save the power by keeping it in sleep state periodically and thereby reducing the overall power consumption of Micro controller. By controlling the sleep time the power consumption is reduced. Whenever it wakes up the program will go to the interrupt and waits for the incoming packet. So the power consumption is reduced by transmitting commands only at its wake up time. The rest of time it will be in the sleep state. The power consumption of the overall system can even be more reduced by the usage of a magnetic sensor in the implant unit. This sensor is programmed as an I/O peripheral of microcontroller. RF Section ON IMPLANT Implant Unit In Human Body RF Section OFF Implant Unit In Human Body Magnetic Material Magnetic Material Magnetic Material Magnetic Material in Doctors hand Fig.6 Implant Unit RF section ON Magnetic Material Magnetic Material in Doctors hand ISSN: Page 385

6 Fig.6.Implant Unit RF section OFF Here first the doctor places a magnetic material near the human body as to make the sensor to sense the magnetism. So after sensing, as per the program we written the RF section of the Implant Unit will come to ON. Now the doctor modifies the pulse of patient by using his Control unit as the RF link got established. After the completion of treatment the doctor makes the RF link between the Control and Implant units off by again keeping the magnet near to the body of patient..thus the unnecessary power consumption of Implant unit can be controlled. C. Transmitter In this thesis the transmitter transmits the commands that modify the receiver pulse. The TIMER, CC1101 Initializations are active by calling them individually when the execution starts. Whenever there is a transmission or reception of the data occurs the program will go to the port _2 interrupt in which GDO pins the interrupt is generated. The GDO pin asserts and de-asserts when there is any data transmission or reception and accordingly the action will be performed. D. Receiver In this work, Receiver unit processes the commands received for their validity and then decodes the commands for identifying action to be performed i.e. varying different parameters of the receiver of simulated data. Receiver is programmed in interrupt mode for CC1101 data, which uses GDO pins for generating interrupts. In detail, When the data is in between $ and # the receiver receives the data and concerned action i.e. pulse amplitude, pulse rate, pulse width accordingly varied. And the acknowledgement for the safe data reception is transmitted back again to the transmitter. Otherwise the loop will again go back and waits for the proper command to receive. This action is performed until the correct data is transmitted. Fig.7 Flowchart of Transmitter The TIMER, CC1101 Initializations are being called. Timer A is initialized in interrupt mode so as to generate interrupt for every 50µs.Pulses are generated using DAC10_DAT register with programmable on time and off times. In the reception program also port _2 GDO pins are used to generate interrupt. By writing 0x36 the device will be in IDLE mode. By writing 0x34 in the command strobe registers the device will go to the receive mode and it is ready to receive incoming packets.0x3b is written to flush the TX FIFO and 0x3A is written to flush the RX FIFO ISSN: Page 386

7 Mode Practical current consumption(micro Amperes) Sleep awake AM LPM LPM LPM LPM LPM A. Result Analysis Table.1 Current consumption in different modes Fig.8 Flowchart of Receiver IV. RESULT Thus the main aim of the thesis, the achievement of Ultra Low Power Consumption is achieved by using the CC430F6147 Micro controller. And also the wireless RF link is established between the two MCs and one unit is controlled by the other. It is depicted from Oscilloscope plots that the pulse amplitude, width, rate of the application unit can be controlled by using the control unit. And the two DAC s of the application unit are controlled independently for all parameters including minimum and maximum thresholds. From the tables shown it is analyzed that the power consuming during the transmission/reception in the normal RX mode that is when there are no active wake on radio or low power modes is ma which is significantly high. By keeping active wake on radio settings the power consumed is reduced to micro amps. And still the power consumption is reduced by introducing low power modes. The power consumed in the LPM4 is still less than that of LPM0/LPM1/LPM2 and LPM3.Also the power consumption is reduced by keeping the unwanted pins in output direction. Where it is increased by keeping in input mode and achieved less than 200 µa of current consumption. Thus the ultra low power micro controller CC430F6147 which has ultimate features of wake on Radio and Low power modes consumes ultra low powers than that of operating in Normal RX mode. V.CONCLUSION It is possible to establish an effective wireless communication between two CC430F6147 Ultra Low Power Micro Controller modules by achieving low power in micro to milli watts based on the application requirement. The communication protocol between pair of units is implemented effectively in command/respond mode with unique identification. ISSN: Page 387

8 The Electrode switching, and varying the pulse amplitude, pulse rate, pulse width is done by sending commands to the application device from the control unit. Hence these modules can be used in applications such as medical implant devices and robotic applications, where battery life is crucial and compact solution is necessary. REFERENCES [1] L.M.Li, H.W.Hao, B.Z.Ma, X.W.Wen, F.J.Liu and C.H.Hu Development of Implantable Neuro-Stimulator Used for Brain and Nerve Stimulation 7 th Asian-PacificConference on Medical and Biological Engineering IFMBE Proceedings Volume 19, 2008, pp [2] An Ultra Low Power, High Performance Medical Implant Communication System (MICS) Transceiver for Implantable Devices Peter D. Bradley Zarlink Semiconductor. (ULP Communications) San Diego, CA, USA [3] SantoshChede and Kishore Kulat Design Overview Of Processor Based Implantable Pacemaker, journal of Computers, vol. 3, no. 8, August 2008 [4] Rahul Sarpeshkar, MichaleS.Fee, SamMusallam and Richard A. Andersen Low-Power Circuits for Brain Machine Interfaces IEEE TRANSACTIONS ONBIOMEDICAL CIRCUITS AND SYSTEMS, VOL. 2, NO.3, SEPTEMBER 2008 [5] Asia-Pacific, Yazdandoost, K.Y.; Med. ICT Inst., Nat. Inst. of Inf. & Commun. Technol., Yokosuka; Kohno, R. Wireless Communications for Body Implanted Medical Device Microwave Conference, APMC [6] Ultralow-Power Electronics for Cardiac Monitoring Lorenzo Turicchia, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I: REGULAR PAPERS, VOL.57, and NO. 9, SEPTEMBER 2010 [7] An Ultra Low Powered MSP430 Microcontroller Based Control System for a Composting Process International Journal of Computer Application ns ( ) Volume 1 No ISSN: Page 388