1 / 11

Lab 4 CRC, PDR vs. distance, preamble sampling

Lab 4 CRC, PDR vs. distance, preamble sampling. Thomas Watteyne EE290Q – Spring 2010 http://wsn.eecs.berkeley.edu/290Q. CRC: Cyclic Redundancy Check. If PKTCTRL0.CRC_EN=1: At Tx , data is hashed and result append to the packet as a 2-byte field

vivek
Download Presentation

Lab 4 CRC, PDR vs. distance, preamble sampling

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lab 4CRC, PDR vs. distance,preamble sampling Thomas Watteyne EE290Q – Spring 2010 http://wsn.eecs.berkeley.edu/290Q

  2. CRC: Cyclic Redundancy Check • If PKTCTRL0.CRC_EN=1: • At Tx, data is hashed and result append to the packet as a 2-byte field • At Rx, data is hashed and result compared to CRC field, packet dropped if fails • How CRC works • Calculate the remainderof a (binary) division • In CC2500,CRC-16-IBM (x16 + x15 + x2 + 1)

  3. CRC: Cyclic Redundancy Check 11010011101100 1011 01100011101100 1011 0111011101100 1011 010111101100 1011 00001101100 1011 0001101100 1011 001101100 1011 01101100 1011 0110100 1011 011000 1011 01110 1011 0101 • Pick a CRC length • e.g. 3 bits • Pick a polynom • e.g. x4+x+1 (1011) • (Always a leftmost 1!) • While bits in data • Write under leftmost data bits • iif leftmost data bit is 1, XOR(leftmost bit always turns to 0) • Shift right one place • Collect 3-bit CRC

  4. The Importance of CRC [1/3] reduce the Tx Power for more frequent errors disable CRC Enable UART lab4_crc #include "radios/family1/mrfi_spi.h" #include "mrfi.h" mrfiPacket_tpacketToSend; int main(void) { BSP_Init(); P1REN |= 0x04; P1IE |= 0x04; MRFI_Init(); mrfiSpiWriteReg(PATABLE,0xBB); mrfiSpiWriteReg(PKTCTRL0,0x41); P3SEL |= 0x30; UCA0CTL1 = UCSSEL_2; UCA0BR0 = 0x41; UCA0BR1 = 0x3; UCA0MCTL = UCBRS_2; UCA0CTL1 &= ~UCSWRST; MRFI_WakeUp(); MRFI_RxOn(); __bis_SR_register(GIE+LPM4_bits); }

  5. The Importance of CRC [2/3] when receiving a packet Copy RXFIFO to “packet” format string send string over serial lab4_crc void MRFI_RxCompleteISR() { uint8_t i; P1OUT ^= 0x02; mrfiPacket_t packet; MRFI_Receive(&packet); char output[] = {" \r\n"}; for (i=9;i<packet.frame[0];i++) { output[i-9]=packet.frame[i]; } TXString(output, (sizeof output)); }

  6. The Importance of CRC [3/3] when button is pressed comment out for continuous Tx Fill frame with ‘abcdef…’ Copy to TXFIFO and send lab4_crc #pragma vector=PORT1_VECTOR __interrupt void Port_1 (void) { P1IFG &= ~0x04; char character = 'a'; uint8_t index; mrfiPacket_t packet; for (index=9;index<30;index++) { packet.frame[index]=character++; } packet.frame[0]=++index; MRFI_Transmit(&packet, MRFI_TX_TYPE_FORCED); P1OUT ^= 0x01; }

  7. Channel Success Probability • Receiver listens • When button pressed sender sends a burst of packets • 100 packets with counter from 1 to 100 • 20 packets with counter to 101 • When receiving a packet • If packet counter <101, increment a counter and store the RSSI • For the first packet with counter==101, display “average RSSI – channel success probability”

  8. Channel Success Probability [1/4] e.g. “-55 0.75” Prepare string transmit string over serial lab4_pdr #include "mrfi.h" uint8_t counter, num_received, bool_counting; int16_t cumulative_rssi; mrfiPacket_t packet; void print_probability(int16_t cumulative_rssi, uint8_t number) { char output[] = {" 000 0.00\n"}; if (cumulative_rssi<0) { output[0]='-'; cumulative_rssi=-cumulative_rssi; } output[1] = '0'+((cumulative_rssi/100)%10); output[2] = '0'+((cumulative_rssi/10)%10); output[3] = '0'+ (cumulative_rssi%10); output[5] = '0'+((number/100)%10); output[7] = '0'+((number/10)%10); output[8] = '0'+ (number%10); TXString(output, (sizeof output)-1); }

  9. Channel Success Probability [2/4] when button is pressed enable serial communication Wait for interrupts in low power mode lab4_pdr int main(void) { BSP_Init(); P1REN |= 0x04; P1IE |= 0x04; MRFI_Init(); mrfiSpiWriteReg(PATABLE,0x50); P3SEL |= 0x30; UCA0CTL1 = UCSSEL_2; UCA0BR0 = 0x41; UCA0BR1 = 0x3; UCA0MCTL = UCBRS_2; UCA0CTL1 &= ~UCSWRST; MRFI_WakeUp(); MRFI_RxOn(); __bis_SR_register(GIE+LPM4_bits); }

  10. Channel Success Probability [3/4] When I receive a packet lab4_pdr void MRFI_RxCompleteISR() { P1OUT ^= 0x02; MRFI_Receive(&packet); counter = packet.frame[9]; if (counter==101) { if (bool_counting == 1) { print_probability(cumulative_rssi/num_received,num_received); } bool_counting=0; num_received=0; cumulative_rssi=0; } else { bool_counting=1; num_received++; cumulative_rssi+=(int8_t) packet.rxMetrics[0]; } }

  11. Channel Success Probability [4/4] when button is pressed lab4_pdr #pragma vector=PORT1_VECTOR __interrupt void interrupt_button (void) { P1IFG &= ~0x04; P1OUT ^= 0x01; mrfiPacket_t packet; packet.frame[0]=8+3; for (counter=1;counter<101;counter++){ packet.frame[9]=counter; MRFI_Transmit(&packet, MRFI_TX_TYPE_FORCED); } for (counter=0;counter<20;counter++){ packet.frame[9]=101; MRFI_Transmit(&packet, MRFI_TX_TYPE_FORCED); } }

More Related