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ECE243

ECE243. LEGO Autobalance LAB. But first: LOGICAL SHIFTS. SLL/SLLI: shift left logical like ‘<<’ in C SRL/SRLI: shift right logical like ‘>>’ in C NOTE: new bits shifted in are zeros Ex: SLLI r8, r9, 0x4 Ex: SRLI r8, r9, 0x3 . Bit Fields and Masking.

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ECE243

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  1. ECE243 LEGO Autobalance LAB

  2. But first: LOGICAL SHIFTS SLL/SLLI: shift left logical like ‘<<’ in C SRL/SRLI: shift right logical like ‘>>’ in C NOTE: new bits shifted in are zeros Ex: SLLI r8, r9, 0x4 Ex: SRLI r8, r9, 0x3

  3. Bit Fields and Masking Use a word, hword, or byte to hold multiple values ex, packing ctrl & data signals into a connector (GPIO) ex, packing small fields to save memory Ex: Course info: department: (ECE, CIV, etc) 12 total => Course code: 0..2000 => Fall, spring: F, S => Better than one halfword each: 3 * 16 bits = 48bits

  4. Course info Example #put dept in r8: #Put course code in r8: #Put F/S in r8:

  5. Next Lab: You will Build a Segway!

  6. Actually, a LEGO Autobalancer

  7. LEGO Setup

  8. LEGO Controller 0 F 0x0 means full light 0xF means low light

  9. LEGO Breakout Box

  10. Autobalancer with Breakout Box

  11. Using Sensors Sensor Sensor Sensor Sensor Sensor 0x0 (full light) 0xF (low light) 0x0 (full light) 0xD (low light) Fixed Distance: 0x7 (some light) Varying Distance:

  12. Talking to LEGO Controler via GPIO • Bits0..9 • configure/control 5 motors • enable/disable; clockwise/counter-clockwise • Bits10..19 • configure/control 5 sensors • Bits27..30 • read data value from sensors • 2 ways to use sensors: • polling mode (default mode, recommended) • state mode (more advanced, see documentation)

  13. Motor control motor4 motor2 motor1 motor0 motor3 motor2 motor1 motor0 motor3 motor4 • for/rev: 0 = forwards/clockwise, 1 = reverse/ctr-clk-wise • on/off: 0 = on, 1 = off 0(JP1): (DR): 4(JP1): (DIR) • set to all 1’s, since they are all outputs

  14. Sensor control sensor4 sensor2 sensor1 sensor0 sensor3 sensor3 sensor2 sensor1 sensor0 sensor4 • on/off: 0 = on, 1 = off • rdy (ready): 0 = ready/valid, 1 = not-ready/invalid 0(JP1): (DR) 4(JP1): (DIR) • set to 1’s for on/off bits (outputs) • set to 0’s for ready bits (inputs)

  15. Sensor values Sensor value Sensor value • 4-bit sensor value • can only read one sensor value at a time • first enable one sensor, then await ‘ready/valid’, then read 0(JP1): (DR) 4(JP1): (DIR) • set direction for sensor value bits to 0’s • since they are inputs

  16. Direction Register DIR • Typical use of DIR: • set to 1(output): • bits0..9 (motor enables), bits10,12,14,16,18 (sensor enables) • set to 0 (input): • bits 11,13,15,17,19 (sensor readys), bits27..30 (sensor value) • Set to 0bxx00 00xx xxxx 0101 0101 0111 1111 1111 • X’s must also be set to certain values (see docs) • Magic number for typical use: (set DIR to this) • 0b0000 0111 1111 0101 0101 0111 1111 1111 • 0x07f557ff

  17. Ex: enable motor1, forward .equ ADDR_JP1, 0x10000060 movia r8,ADDR_JP1 movia r9, 0x07f557ff # set DIR to typical-use value stwio r9, 4(r8) movia r9, 0xfffffff3 # 0b... 11110011 # bit2=0 for enabled, bit3=0 for forward stwio r9,0(r8)

  18. Ex: read sensor2 .equ ADDR_JP1, 0x10000060 movia r8,ADDR_JP1 movia r9, 0x07f557ff # set DIR to typical-use value stwio r9, 4(r8) movia r9, 0xffffbfff # bit14=0 to enable sensor2 stwio r9,0(r8) POLL ldwio r9,0(r8) # read DR srli r10,r9,15 # shift bit-15 to the bit-0 position andi r10,r10,0x1 # mask it to isolate it bne r10,r0,POLL # ready if r10==0, try again otherwise srli r9,r9,27 # shift-right-logical-immed by 27 bits # sensor value is now in lowest 4 bits of r9 andi r9,r9,0x0000000f # mask it to isolate it # can now use sensor value in r9

  19. Some Hints • Do not use delay counters, must use timer • Not all sensors are equal • sensitivities vary, you must calibrate them • motors will stall if you switch directions fast • motors can be too fast/jerky: • if you give it full voltage: • instead give it part voltage: • called Pulse Width Modulation (PWM) • See DESL for full details! • page on Lego Controller (quick reference) • full Lego manual (pdf)

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