Application Note AN053 AN053 Measuring power consumption with CC2430 & Z-Stack By B.Selvig Keywords • Power Saving • CC2430 • ZigBee • Z-Stack • Power Mode 1 Introduction This document describes power consumption measurements for a CC2430 node running ZStack. Sample applications in Z-Stack that implements the Home Automation ZigBee profile has been used for these measurements. The measurement setup consists of a ZigBee End Device and a Coordinator. The End Device will periodically poll the Coordinator for data, and in between the polls the device goes to sleep to save power. This document describes how to set up the Z-Stack firmware for the End Device and the Coordinator node, as well as the hardware setup for the measurements. Section 4 presents the results of the power consumption measurements performed on the End Device node. It also presents an estimation of battery life time for two given example scenarios. Since many factors influence on the power consumption, the results in this document are intended as an indication of the power consumption under the given setup only. AN053 (Rev. 1.0) SWRA144 Page 1 of 17 Application Note AN053 Table of contents Keywords ................................................................................................................................................1 1 Introduction .....................................................................................................................................1 Table of contents ...................................................................................................................................2 2 Abbreviations..................................................................................................................................2 3 Measurement Setup ......................................................................................................................3 3.1 Firmware ...................................................................................................................................5 3.1.1 Coordinator node ...........................................................................................................5 3.1.2 End Device (Device Under Test) .................................................................................5 4 Measurements................................................................................................................................7 4.1 Poll with no data transmission...............................................................................................7 4.2 Poll with data transmission ..................................................................................................11 5 Battery life time calculation.........................................................................................................14 5.1 Battery life calculation with polling rate 1 second.............................................................14 5.2 Battery life calculation with polling rate 1 minute..............................................................15 6 Conclusion ....................................................................................................................................16 7 References ...................................................................................................................................16 Document History ................................................................................................................................16 Important Notice...................................................................................................................................17 2 Abbreviations The following abbreviations are used in this document: CSMA/CA DB EM HA IAR EW MAC MCU RX TX Z-Stack Carrier Sense Multiple Access with Collision Avoidance Demonstration Board Evaluation Module Home Automation ZigBee profile IAR Embedded Workbench, see www.iar.com Medium Access Control (layer) Microcontroller Unit Receive Transmit Texas Instruments ZigBee protocol stack AN053 (Rev. 1.0) SWRA144 Page 2 of 17 Application Note AN053 3 Measurement Setup This section describes the measurement setup and how to configure the firmware to be programmed in the devices. Please refer to Figure 1. Note: In the setup used throughout the document the End Device is running a light controller application, and the Coordinator a light switch application. Even though it would seem more realistic with the light switch as a battery powered End Device, and not the light controller, this setup is intended to be general for battery powered devices polling its parent. This type of device can be used in many types of applications. The specific setup in these measurements is not meant as a specific real scenario, but rather as a way of measuring current consumption in a generic battery powered End Device running Z-stack and CC2430. 1 CC2430DB is programmed as Coordinator with the Home Automation SampleSwitch application. 1 CC2430EM is programmed as End Device with the Home Automation SampleLight application. Measurements of current consumption are performed on this node. The current consumption varies rapidly and to estimate the average current consumption, the current is measured with an oscilloscope voltage probe over a 10Ω resistor in series with the power supply. The use of the resistor and oscilloscope allows measurement of the current consumption as a function of time, and is therefore necessary to calculate battery life time. This method also gives a visual representation of the current consumption during active and sleep mode of the device. Note: This measurement method may influence the result because of the voltage drop over the resistor and the stray (cable) resistance. Ideally the measurement setup should have been verified with a high precision amperemeter. However the accuracy will be defined by other factors and a higher accuracy here would not affect the final results. The results are also read manually from the oscilloscope, which will also influence on the accuracy. AN053 (Rev. 1.0) SWRA144 Page 3 of 17 Application Note AN053 Textronix TDS224 Oscilloscope ZigBee SampleSwitch (Coordinator) CC2430DB 1 2 Power supply HP E3630A - + Resistor 10Ω, 1% ZigBee SampleLight (EndDevice) CC2430EM Figure 1 Measurement setup The measurements are performed using Z-Stack 1.4.1 and CC2430 revision E. In order to repeat the measurements download and install Z-Stack and Z-Stack apps for CC2430/2431. Please read the Important Notice section on the Z-Stack download website: www.ti.com/zstack In the Z-Stack 1.4.1 release, the core and apps installations must be merged before the applications can be used. Please read Z-Stack Applications User's Guide [1] for information about how this is done. The current consumption measurements are performed on the End Device on a standalone EM board not connected to any other board. The board is powered from the connectors underneath; GND to P2 pin 2 and VDD +3.0 V to P2 pin 9. AN053 (Rev. 1.0) SWRA144 Page 4 of 17 Application Note AN053 3.1 Firmware The following sections describe how to setup, compile and download firmware to the Coordinator and End Device node. The default settings for the SampleLight project has power saving disabled. These instructions describe how to set up the project with power saving enabled on the End Device. Note: In order to open the Z-Stack projects and program the hardware the IAR EW for 8051 is needed. Either the full version or the time limited evaluation version of IAR EW can be used. 3.1.1 • • Coordinator node Open the workspace file SampleSwitch.eww with IAR EW. Choose the Coordinator configuration for the correct hardware used. There will be performed no current measurements on this hardware, so either a CC2430DB or SmartRF04EB with a CC2430EM can be used. Program the board: Press Project->Debug 3.1.2 End Device (Device Under Test) 1. Open the workspace file SampleLight.eww with IAR EW. Choose the EndDeviceEB configuration. 2. Set correct linker file for power saving. Choose the Project tab and Options->Linker>Config. Set the linker file to $PROJ_DIR$\..\..\..\Tools\CC2430DB\f8w2430pm.xcl. Figure 2 Linker command file AN053 (Rev. 1.0) SWRA144 Page 5 of 17 Application Note AN053 3. Set Defined Symbols: Choose the Project tab and Options->C/C++ Compiler>Preprocessor. Include these defined symbols to define the hardware that is used and to enable network polling and power saving: CC2430EB NWK_AUTO_POLL POWER_SAVING Figure 3 Defined Symbols 4. Set the Poll Rate for the End Device. This parameter defines how often the node will wake up from sleep and send a data request to the parent device to poll for queued messages. In these measurements the Poll Rate is set to 500 ms. Set the Poll Rate in f8wConfig.cfg in line 141: /**************************************** * The following are for End Devices only ***************************************/ -DRFD_RCVC_ALWAYS_ON=FALSE /* The number of milliseconds to wait between data request polls to the coordinator. */ -DPOLL_RATE=500 5. Turn off Key polling. This is done by enabling key interrupt. In the file Onboard.c, function InitBoard( byte level ) enable interrupt by changing the following line: OnboardKeyIntEnable = HAL_KEY_INTERRUPT_DISABLE; AN053 (Rev. 1.0) SWRA144 Page 6 of 17 Application Note AN053 To this: OnboardKeyIntEnable = HAL_KEY_INTERRUPT_ENABLE; 6. Connect the EM module to a SmartRF04EB. The SmartRF04EB board must be connected to the PC with a USB cable. 7. Program the board: Press Project->Debug 8. Remove the EM module from the SmartRF04EB and connect it according to the measurement setup shown in Figure 1 4 Measurements In these measurements the End Device is set up to poll the Coordinator for data every 500 ms. The device will sleep in between the poll requests, using CC2430 Power Mode 2. Every 500 ms the device wakes up on sleep timer interrupt and sends the data request to poll for data. The power consumption for the polling sequence when the Coordinator has no buffered data to the End Device is measured in section 4.1. The power consumption during a polling sequence where the Coordinator has data to the End Device is measured in section 4.2. The current consumption during wake up, transmission and reception on the End Device is measured with an oscilloscope. The parameters for the measurements are summarized below: • Chip revision: CC2430 rev. E • Z-Stack version: Z-Stack core 1.4.1, Z-Stack apps 1.0.0 • End Device application: SampleLight • Coordinator application: SampleSwitch • Poll Rate: 500 ms 4.1 Poll with no data transmission Figure 4 Packet sniffer plot AN053 (Rev. 1.0) SWRA144 Page 7 of 17 Application Note AN053 Figure 4 shows the captured plot from the Chipcon Packet Sniffer. This plot shows the data request packets from the End Device and the MAC layer acknowledgements from the Coordinator node with an interval of approximately 500 ms. Figure 5 Data requests and acknowledgements Figure 5 shows the power consumption during sleep and awake. The time base on the oscilloscope is set to 200 ms per division, and it can be seen from the figure that it is approximately 500 ms between each current peak, as the poll rate defines. The current peaks shows the power consumption when the device is awake to send the data request and to receive the acknowledgement. The low steady current between the peaks is the current consumption during sleep mode (Power Mode 2). This current is measured to approximately 0.5 uA with an ampere-meter which is in conformance with value from the CC2430 data sheet [2]. AN053 (Rev. 1.0) SWRA144 Page 8 of 17 Application Note AN053 Figure 6 Power consumption during data requests and acknowledgement Figure 6 is a zoomed version of Figure 5 and shows the current consumption during the active modes in more details. This plot has a time base of 1 ms per division. The duration of the active mode is measured to be approximately 7.58 ms with the oscilloscope. Note that this duration will have some variation between each poll interval. AN053 (Rev. 1.0) SWRA144 Page 9 of 17 Application Note AN053 Figure 7 intervals Figure 7 is exactly the same as Figure 6 with the different intervals during active mode enumerated. Table 1 below gives approximate values for the duration of each of these intervals and their current consumption. Note that not all these intervals will have constant duration. The duration and current values in Table 1 are observed with an oscilloscope and serve as an example. Please also refer to the datasheet for typical current consumption values during the various MCU and Radio modes. Table 1 Duration and current values for the intervals Interval 1 2 3 4 5 6 7 8 9 Description Start up sequence. MCU in active mode running on 16 MHz clock MCU running on 32 MHz clock. CMSA/CA algorithm. Radio in RX mode. Switch from RX to TX. Packet transmission. Radio in TX mode. Switch from TX to RX. Reception of acknowledgement from Coordinator. Radio in RX mode. Packet processing. MCU running on 32 MHz clock. Shut down sequence (PM0->PM2). MCU running on 16MHz clock AN053 (Rev. 1.0) SWRA144 Current 0.75 mA Duration 0.49 ms 12 mA 31 mA 18 mA 29 mA 18 mA 31 mA 1.8 ms 1.6 ms 0.19 ms 0.58 ms 0.11 ms 1.1 ms 12 mA 1.1 ms 7 mA 0.62 ms Page 10 of 17 Application Note AN053 The duration of interval 3, when the device performs the CSMA/CA algorithm, may vary if the channel is noisy. This is due to the random interval the device will defer from sending when the medium is sensed to be busy or noisy. The mean value of Interval 3 under the given channel conditions is estimated by taking 20 observations. The average of these 20 observations is 1.06 ms, in the range between 200 us and 2.45 ms. The total power consumption for one cycle of 500 ms is estimated below based on the observed values in Table 1, and the observed mean value of Interval 3. Using this observed mean value the total duration of the active period is 7.05 m. + + + + + + + + Interval 1: Interval 2: Interval 3: Interval 4: Interval 5: Interval 6: Interval 7: Interval 8: Interval 9: 0.75 mA * 0.49 ms 12 mA * 1.8 ms 31 mA * 1.06 ms 18 mA * 0.19 ms 29 mA * 0.58 ms 18 mA * 0.11 ms 31 mA * 1.1 ms 12 mA * 1.1 ms 7 mA * 0.62 ms = = = = = = = = = 0.3675 21.6 32.86 3.42 16.82 1.98 34.1 13.2 4.34 [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] Total power consumption per polling (only active period) without data transmission: ≈ 4.2 128.7 [mA*ms] Poll with data transmission Assume the Coordinator has a data packet buffered to the End Device. When the End Device wakes up from sleep it will poll the Coordinator, and the Coordinator sends the buffered packet to the End Device. The sequence of packets is shown in the captured plot from the Chipcon Packet Sniffer in Figure 8 below. The End Device first sends a data request packet to poll the Coordinator for data. The Coordinator responds with a MAC layer acknowledgement. The third packet is the data packet from the Coordinator. In this case it is an On/Off command to the HA light controller. The fourth packet is the MAC layer acknowledgement from the End Device, followed by the application layer acknowledgement from the End Device. The last packet is the MAC layer acknowledgement from Coordinator. Figure 8 Data transmission and application layer acknowledgement AN053 (Rev. 1.0) SWRA144 Page 11 of 17 Application Note AN053 Figure 9 Power consumption during data reception and application layer acknowledgement transmission Figure 9 shows the power consumption on the End Device for the same sequence of packets as in Figure 8. AN053 (Rev. 1.0) SWRA144 Page 12 of 17 Application Note AN053 Table 2 Interval 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Description Start up sequence. MCU in active mode running on 16 MHz clock MCU running on 32 MHz clock. CMSA/CA algorithm. Radio in RX mode. Switch from RX to TX. Packet transmission. Radio in TX mode. Switch from TX to RX. Reception of data packet from Coordinator. Radio in RX mode. Switch from RX to TX. Transmission of MAC layer acknowledgement. Radio in TX. Packet processing. MCU running on 32 MHz clock. CMSA/CA algorithm. Radio in RX mode. Switch from RX to TX. Transmission of application layer acknowledgement. Radio in TX. Switch from TX to RX. Reception of MAC layer acknowledgement Packet processing. MCU running on 32 MHz clock. Shut down sequence. MCU running on 16MHz clock Current 0.75 mA Duration 0.49 ms 12 mA 31 mA 18 mA 29 mA 18 mA 31 mA 1.8 ms 0.9 ms 0.19 ms 0.58 ms 0.11 ms 5.2 ms 18 mA 29 mA 0.19 ms 0.36 ms 12 mA 5,1 ms 31 mA 18 mA 29 mA 1.5 ms 0.19 ms 1.1 ms 18 mA 31 mA 12 mA 0.11 ms 0.97 ms 1.1 ms 7 mA 0.62 ms Table 2 gives the observed duration and current values for the intervals of the sample shown in Figure 9. As discussed under section 4.1 the duration of the CSMA/CA algorithm may vary if the channel is noisy or busy. The CSMA/CA algorithm takes place in Interval 3 and 11 in Table 2. In the following calculation the observed average value for Interval 3 used in section 4.1 will be used. AN053 (Rev. 1.0) SWRA144 Page 13 of 17 Application Note AN053 The total power consumption for one poll interval with data transmission is estimated based on observed values below: + + + + + + + + + + + + + + + + Interval 1: Interval 2: Interval 3: Interval 4: Interval 5: Interval 6: Interval 7: Interval 8: Interval 9: Interval 10: Interval 11: Interval 12: Interval 13: Interval 14: Interval 15: Interval 16: Interval 17: 0.75 mA * 0.49 ms 12 mA * 1.8 ms 31 mA * 1.06 ms 18 mA * 0.19 ms 29 mA * 0.58 ms 18 mA * 0.11 ms 31 mA * 5.2 ms 18 mA * 0.19 ms 29 mA * 0.36 ms 12 mA * 5.1 ms 31 mA * 1.06 ms 18 mA * 0.19 ms 29 mA * 1.1 ms 18 mA * 0.11 ms 31 mA * 0.97 ms 12 mA * 1.1 ms 7 mA * 0.62 ms = = = = = = = = = = = = = = = = = Total power consumption per polling with data transmission: ≈ 5 0.3675 21.6 32.86 3.42 16.82 1.98 161.2 3.42 10.44 61.2 32.86 3.42 31.9 1.98 30.07 13.2 4.34 [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] [mA*ms] 431.1 [mA*ms] Battery life time calculation The battery life time for a ZigBee End Device is heavily dependent on poll rate and how often it will receive a data packet. A higher poll rate will result in higher power consumption. The power consumption per polling with no data transmission was calculated in section 4.1 to be 128.7 [mA*ms]. The average duration the End Device is awake during a polling sequence with no data is 7.05 ms. This value is found by summarizing the duration of the intervals 1-11 from the calculation in section 4.1. For Interval 3 the estimated value of 1.06 ms is used. With data transmission the power consumption per polling was calculated in section 4.2 to be 431.1 [mA*ms]. The average duration the End Device is awake during a polling sequence with data is 20.23 ms. This value is found by summarizing the duration of the intervals 1-17 from the calculation in section 4.2. For Interval 3 and 11 the estimated average value of 1.06 ms is used. The power consumption during sleep mode must be added to the active mode power consumption. The duration of each sleeping period is the polling period minus the duration of the relevant active mode. The current consumption during Power mode 2 is 0.5 uA according to the CC2430 datasheet [2]. 5.1 Battery life calculation with polling rate 1 second In this example it is assumed that there is data for the node twice per day on average. In the calculations below, the poll rate is set to 1 second. AN053 (Rev. 1.0) SWRA144 Page 14 of 17 Application Note AN053 The total power consumption per day is calculated below: Polling with no data: 128.7 mAms × ((60 / min× 60 min/ H × 24 H / day ) − 2) /(1000ms / s ) /(3600 s / H ) ≈ 3.0887mAH / day + Polling with data two times per day: 431.1mAms × 2 / day /(1000ms / s ) / 3600 s / H ≈ 0.0002 + Power consumption during sleep: 0.0005mA × (1000ms − 7.05ms ) × ((60 × 60 × 24) − 2) / day / 1000ms / s / 3600 + 0.0005mA × (1000ms − 20.23ms ) * 2 / day / 1000ms / s / 3600 s / H ≈ 0.0119mAH / day Summarizing these values gives: Total: ≈ 3.1008 [mAH/day] The average current over the day is: 3.1008mAH / day /( 24 H / day ) = 129.2uA The resulting battery life time using two AA batteries with 3100 mAH true capacity is calculated to: 3100 [mAH] / 3.1008 [mAH/day] ≈ 1000 days Note: One AA battery will only provide 1.5 volts, and therefore 2 batteries are needed to get 3.0 volts. Since the current consumption of the CC2430 is almost independent of input voltage a lower voltage gives a better power consumption if a converter is uses. One 1.5V battery with a 90% effective switch mode voltage converter and 2.0 V output would give a battery life time of 1000 days * (1.5/2.0 * 0.9) = 675 days (if battery voltage was constantly 1.5 V throughout the life time). 5.2 Battery life calculation with polling rate 1 minute The same calculation as above but with a polling rate of once per minute instead will give: Polling with no data: 128.7 mAms × ((1 / min× 60 min/ H × 24 H / day ) − 2 /(1000ms / s ) /(3600 s / H ) ≈ 0.05141mAH / day + Polling with data two times per day: ≈ 0.0002 + Power consumption during sleep: 0.0005mA × (60 × 1000ms − 7.05ms ) × ((60 × 24) − 2) / day / 1000ms / s / 3600 ≈ 0.0120mAH / day Summarizing these values gives: Total: AN053 (Rev. 1.0) ≈ SWRA144 0.06361 [mAH/day] Page 15 of 17 Application Note AN053 The average current over the day with polling rate of 1 minute is: 0.06361mAH / day /( 24 H / day ) = 2.65uA The resulting theoretical battery life time using two AA batteries with 3100 mAH true capacity is calculated to: 3100 [mAH] / 0.06361 [mAH/day] ≈ 48734 days which is approximately 134 years. This battery life is only theoretical since battery cells normally does not last that long for other reasons than current consumption from the application. Note: In this calculation the power consumption during network start up and commissioning is not taken into account. 6 Conclusion The measurements in the above examples are intended as an indication of expected power consumption and battery life time under the given conditions. Two factors that influence the power consumption strongly are the poll rate and the channel conditions. These measurements are performed in an office environment with much RF traffic. This will strongly influence the duration of the interval 3 in Table 1, and Interval 3 and 11 in Table 2. The short startup and transmission times of the TI products assures long battery lifetime. In cases with interfering traffic on the channel in use, retransmissions of either data requests, acknowledgement packets or data packets may occur. When retransmission occurs it will influence the power consumption to an extent that is dependent on how often packets need to be retransmitted in average. The battery life time may be extended by decreasing the poll rate when this is acceptable in the application. In the above examples it is assumed that the data traffic goes only one way, from the Coordinator to the End Device. The length of the data packets transmitted from the Coordinator also influences the power consumption, because it directly influences the time used to receive the packet. The complexity of the application, and which peripherals that are used, will also influence the power consumption. 7 References [1] Z-Stack Applications User's Guide_F8W-2007-0022_.pdf. This document is found in the documents folder in the Z-Stack installation folder. www.ti.com/z-stack [2] CC2430 Preliminary Data Sheet (rev. 2.01) SWRS036E http://focus.ti.com/docs/prod/folders/print/cc2430.html Document History Revision 1.0 Date 2007.07.08 Description/Changes Initial release. AN053 (Rev. 1.0) SWRA144 Page 16 of 17 Application Note AN053 Important Notice Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. 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