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# COMP ARCHITCTR & EMBEDDED SYSTMS CS 179J

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This 3 page Class Notes was uploaded by Adele Schaden MD on Thursday October 29, 2015. The Class Notes belongs to CS 179J at University of California Riverside taught by Staff in Fall. Since its upload, it has received 36 views. For similar materials see /class/231753/cs-179j-university-of-california-riverside in ComputerScienence at University of California Riverside.

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Date Created: 10/29/15
CS 179J Project in Architecture Embedded Systems Power Estimation Example Equations I Defenitions P VI P power in watts V voltage in volts l current in amperes 1 W 1 Js 1 watt is equaled to1 Joule per second E Pt E energy in joules P power in watts t time in seconds Battery Battery used in eBlocks Duracell 9V MN1604 According to mousercom a 9V Duracell Alkaline battery contains 565 mAh 9 V 595 mAh 5355 mWh wl u w MUM L L L theAVreduces to W 5355 mWh 3600 sechr 11000 19278 W5 we get rid of the m by dividing by 1000 and convert Wh to Ws by multiplying by 3600 19278 W5 19278 Joules 1 W 1 Js orilwe change things around 1 Ws 1 J Thus the energy contained in a 9V battery is 19278 Joules PIC processor PIC Processor used in eBlocks PC16F628 We look at microchipcom to find the datasheet for the corresponding PIC characteristics Normal Operating Voltage 5V Normal Operating Current 20 uA Power Down Current 02 uA Watch Dog Timer Current 6 uA drive a high on output port 3 mA drive a low on output port 85 mA bits transmitted in single packet start bit bit0 bit1 bit2 bit3 stop bit gt 6 bits Assummption 5 instructions to send 1 bit 6 bitspacket 5 instructionsbit 30 instructions to send a packet Given default c k speed it takes 1 u second instruction 30 u seconds to send a packet Energy Estimation We first gure out the current required to transmit a packet for simplicity we assume the packet consists soley of 039s tx current current to drive port low during transmission PlC operating current 85 mA 20 uA 00085 A 0000020 A 000852 A When the processor is not transmitting a packet it goes to power down for remaining time If we use power down feature we must factor in watchdog timer to wake up processor wdt is off during tx total power down current PlC power down current watch dog timer current 020 uA 6 uA 62 uA Now we gure out how much time is spent transmitting and how much time is spent in power down Assume we tx a packet every 3 seconds 39 86400 sec per day3 s 28800 tx per day 28800 tx per day 30 uS per tx 0864 seconds per day spend on tx of packets 86400 seconds per day 0864 seconds per day spent on tx of packet 86399136 seconds per day spent in power down mode Now we figure out the energy associated with transmitting and power down energy for transmit 5V 000852A 0864 seconds 00368 Joules for tx per day power down energy 5V 00000062A 86400 0864 seconds 2678 Joules for idle operation per day No to figure out the estimated battery lifetime 19278 Joules in a 9V battery00368 J 2678 J 7101076 days battery will last 7101 076 days if we tx once every 3 seconds and proceesor power down remaining time Exercise Try to gure out the estimated battery life of a 2input logic block eBlock 2 inputs 1 output tx current 000852 A these are from the previous example total power down current 00000062 uA seconds spent on tx 0864 seconds per day energy for transmit 00368 Joules for tx per day rx current PIC operating current 20 uA seconds spent on rx 0864 seconds per day the seconds spend on rx should match tx it39s recieving what39s sent energy for rx 5V 000002A 0864 seconds 00000864 Joules for rx per day power down energy 5V 00000062A 86400 0864 3 seconds 2678 Joules for idle operation per day 19278 Joules in a 9V battery00368 J 00000864 J 2 2678 J 7100623 days battery will last 7100623 days worst case assumption Try to gure out the estimated battery life of an led eBlock 1 input The led requires 21 volts and draws 20 mA Assume the led is on 30 of the day rx current PIC operating current seconds spent on rx 0864 seconds per day the seconds spend on rx should match tx it39s recieving what39s sent energy for rx 5V 000002A 0864 seconds 00000864 Joules for rx per day CS 179J Project in Architecture Embedded Systems Power Estimation Example Equations I Defenitions P VI P power in watts V voltage in volts l current in amperes 1 W 1 Js 1 watt is equaled to1 Joule per second E Pt E energy in joules P power in watts t time in seconds Battery Battery used in eBlocks Duracell 9V MN1604 According to mousercom a 9V Duracell Alkaline battery contains 565 mAh 9 V 595 mAh 5355 mWh wl u w MUM L L L theAVreduces to W 5355 mWh 3600 sechr 11000 19278 W5 we get rid of the m by dividing by 1000 and convert Wh to Ws by multiplying by 3600 19278 W5 19278 Joules 1 W 1 Js orilwe change things around 1 Ws 1 J Thus the energy contained in a 9V battery is 19278 Joules PIC processor PIC Processor used in eBlocks PC16F628 We look at microchipcom to find the datasheet for the corresponding PIC characteristics Normal Operating Voltage 5V Normal Operating Current 20 uA Power Down Current 02 uA Watch Dog Timer Current 6 uA drive a high on output port 3 mA drive a low on output port 85 mA bits transmitted in single packet start bit bit0 bit1 bit2 bit3 stop bit gt 6 bits Assummption 5 instructions to send 1 bit 6 bitspacket 5 instructionsbit 30 instructions to send a packet Given default c k speed it takes 1 u second instruction 30 u seconds to send a packet Energy Estimation We first gure out the current required to transmit a packet for simplicity we assume the packet consists soley of 039s tx current current to drive port low during transmission PlC operating current 85 mA 20 uA 00085 A 0000020 A 000852 A When the processor is not transmitting a packet it goes to power down for remaining time If we use power down feature we must factor in watchdog timer to wake up processor wdt is off during tx total power down current PlC power down current watch dog timer current 020 uA 6 uA 62 uA

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