1 / 31

Wireless Transceiver

Wireless Transceiver. EECS150 Spring 2007 Lab Lecture #9 Neil Warren. Transceiver Overview (1). 3 rd party chip mounted on expansion board. Uses a PCB antenna. Take a look! IEEE 802.15.4 standard support. Zigbee ready.

mathiss
Download Presentation

Wireless Transceiver

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. Wireless Transceiver EECS150 Spring 2007 Lab Lecture #9 Neil Warren EECS150 Spring 2007 - Neil Warren

  2. Transceiver Overview (1) • 3rd party chip mounted on expansion board. • Uses a PCB antenna. Take a look! • IEEE 802.15.4 standard support. Zigbee ready. • Transmits on unlicensed 2.4 GHz spectrum. 16 communication channels. • Overlaps with Wi-Fi. • 250 kbps maximum data rate. • Configure, send, receive, and issue commands to chip over SPI to CC2420 registers. EECS150 Spring 2007 - Neil Warren

  3. Transceiver Overview (2) • 33 configuration registers. • We change 3 of them. • 15 command strobe registers. • We issue 6 of them. • These change the state of the CC2420 internal FSM. • 128-byte RX FIFO & 128-byte TX FIFO • Accessed via 2 additional registers. • Also accessible as RAM (i.e. by addressing). Only for debugging! Don’t do this unless you’re a masochist EECS150 Spring 2007 - Neil Warren

  4. Transceiver Overview (3) • You will need to read the data sheet to learn more about how the CC2420 works in more detail than what we can fit in the Spec. • MDPU • Status Registers (more info.) • Commands (more info.) • Internal state machine (very helpful!!) EECS150 Spring 2007 - Neil Warren

  5. CC2420 Inputs & Outputs • Single bit status signals. • High level transceiver operation information. • Initialization signals. • Drive signals once and forget about it. • SPI interface. • Interface to rest of chip via CC2420 registers. • Send, receive, configuration, detailed status. FPGA VREG_EN RF_RESET_ EECS150 Spring 2007 - Neil Warren

  6. Single Bit Status Indicators • FIFO – Goes high when there’s received data in RX FIFO. • FIFOP – Goes high when # bytes received exceeds set threshold. • CCA – Indicates that the transmission medium (air) is clear. Only valid after 8 symbol periods in RX mode. • SFD – Goes high after SFD is transmitted & low after packet completely sent. EECS150 Spring 2007 - Neil Warren

  7. SPI Interface • Serial interface with 4 wires: • SClk – Clock signal you generate. • CS_ – Active-low chip select. • SI – Output to the CC2420. • SO – Input from the CC2420. • Interface to the chip! Initialization, configuration, TX, RX, detailed status. • Luckily for you, it’s provided as a black box. EECS150 Spring 2007 - Neil Warren

  8. CC2420-specific SPI (1):First Byte • First byte always has above format. • Bit 7 – Set to 0 for register access. • Bit 6 – Read/write control. • Bits 5:0 – Address of register. P. 60 of datasheet. • Followed by data specific to register being accessed. EECS150 Spring 2007 - Neil Warren

  9. CC2420-specific SPI (2):Writing to Configuration Reg. • First byte followed by 2 bytes of configuration data. • Data on SO invalid here. • Transceiver replies when first byte is sent out with status byte. • True for all SPI accesses. • Not necessary to inspect, but can be helpful for debugging! EECS150 Spring 2007 - Neil Warren

  10. CC2420-specific SPI (3):Issuing Command Strobes • One byte only. Nothing follows. • Address sent indicates the command strobe being issued. • Note that 0x00 is NO OP. This is useful for explicitly retrieving status byte. EECS150 Spring 2007 - Neil Warren

  11. CC2420-specific SPI (4):Saving to TX FIFO • After first byte, send n bytes of data to transmit over wireless. • SPI session only ends when CS_ is pulled high. • CC2420 replies with a new status byte with each byte that’s saved to FIFO. EECS150 Spring 2007 - Neil Warren

  12. CC2420-specific SPI (5):Receive from RX FIFO • After first byte, send a n bytes of “don’t care” in order to receive data. • During first byte, CC2420 replies with status. Subsequent bytes are data saved in FIFO. • Must be careful not to request data from empty FIFO! • SPI session only ends when CS_ is pulled high. • Reading from a configuration register is the same. EECS150 Spring 2007 - Neil Warren

  13. Configuration Registers EECS150 Spring 2007 - Neil Warren

  14. Command Strobe Registers EECS150 Spring 2007 - Neil Warren

  15. TX/RX FIFO Registers EECS150 Spring 2007 - Neil Warren

  16. Initialization EECS150 Spring 2007 - Neil Warren

  17. Transmit EECS150 Spring 2007 - Neil Warren

  18. Transmit(2) • CC2420 needs 12 symbol periods to move into RX_SFD_SEARCH state after transmit done or SRXON. • 1 symbol period = 16 us. • Without enforcing wait, aggressive user of your Transceiver module will cause CC2420 to never receive data from air. EECS150 Spring 2007 - Neil Warren

  19. CCA • If you don’t follow CCA we will dock MAJOR points • If CCA isn’t high, you must wait a RANDOM AMOUNT OF TIME • CCA may also not go high if you have buffer overflow. FIFOP & !FIFO EECS150 Spring 2007 - Neil Warren

  20. Receive (1) EECS150 Spring 2007 - Neil Warren

  21. Receive (2) • You must be able to receive while the random CCA wait time is expiring! • Packets are only received after CC2420 has spent 12 symbol periods in receive mode. • There must be wait time between transmissions. • Allows the transceiver to look for and receive data. EECS150 Spring 2007 - Neil Warren

  22. Receive(3) • Refers to 2 things: • CC2420 is constantly receiving and saving data into RX FIFO as long as it’s not transmitting. Look at CC2420 internal FSM on p. 43. • You have to “receive” data from RX FIFO, filter it, then save wanted data into SPIFifo. EECS150 Spring 2007 - Neil Warren

  23. Design Structure (2) • Transceiver – Highest level block. 32-bit input/output, channel changing, addressing. • SPI Abstraction – Takes care of details of CC2420 SPI interface. Arbitrates between TX/RX. • SPI (provided) – Handles details of interface timing. EECS150 Spring 2007 - Neil Warren

  24. Packet Format • On transmit, only fill TX FIFO starting with length byte. • Preamble & SFD automatically appended. • Transmit all zeros for CRC. CC2420 will replace. EECS150 Spring 2007 - Neil Warren

  25. Channel & Addresses • There are 16 channels. • Your group will be assigned a channel. • You must be able to change channels without reset! • DO NOT USE ANOTHER CHANNEL BESIDES YOUR OWN • This is a big class and we need to be able to partition the signal space! • Address are 8-bits wide  256 addresses. Zero is unused. 0xFF is reserved for broadcast. EECS150 Spring 2007 - Neil Warren

  26. Interference & Debugging • Roughly 2-3 groups per channel. Each group in a particular lab has distinct channel. • Can also pick up data on neighboring channel. • Very first goal is robust channel changing during initialization. • Can pick up 802.11 packets sometimes. • Your module must recover gracefully. • Your project interferes with Wi-Fi & vice versa. EECS150 Spring 2007 - Neil Warren

  27. Handshaking:InRequest/Invalid • SPI uses a variation of this. • You may want to use this internally. EECS150 Spring 2007 - Neil Warren

  28. Handshaking:Ready/Start • Transceiver uses this interface for input & output. EECS150 Spring 2007 - Neil Warren

  29. Debugging Tools • Chipscope! • We will be releasing some debugging utilities. • Packet sniffer. • Packet counter (The TA Solution does this) EECS150 Spring 2007 - Neil Warren

  30. Get Started! • READ THE DATASHEET • Obey our CCA rules EECS150 Spring 2007 - Neil Warren

  31. Danger! Danger! • Don’t become complacent because you’ve *been* finishing checkpoints early • Expect each checkpoint to be at least twice as difficult as the last. • 1>>2>>>>3>>>>>>>>4! • Get started early and get ahead. EECS150 Spring 2007 - Neil Warren

More Related