Description

Neo Lou and Ethan Fong
1. Read the following documents to learn how to interface with both the Lego controller and the timer:
a. Lego Controller Device Documentation
b. Timer Documentation
0x17fff80, since the stack grows to lower addresses and there is free memory here and we don’t use many of the addresses before it. According to the memory map it’s in the region of 64 MB SDRAM.
3. Answer the following questions about bit masking:
a. Write assembly instruction(s) to set bit 11 (assume 0 indexed) of r2 to 1, without changing other bits
movia r3, 0x800 #1000 0000 0000 or r2, r2, r3
b. Write assembly instruction(s) to set bit 8 (assume 0 indexed) of r2 to 0, without changing other bits
movia r3, 0xFFFFFEFF # … F 1110 F F and r2, r2, r3
4. Answer the following questions, assuming the Lego controller is plugged into JP1:
a. To properly configure the Lego controller I have to write the value 0x07f557ff (motors and sensors) to the direction register, which is located at address 0xFF200064 (DIR register) .
Bits 26 downto 21 and 18,16,14,12,10 downto 0 must be set to 1’s outputs
Bits 31 downto 27,19,17,15,13,11 must be set to 0’s inputs.
b. To turn on motor 2 I have to set bits 4/5 (fwd/on) at memory location 0xFF200060 to the value 00.
c. Give an example of a 32-bit value that will enable sensor 1 for reading when written to the GPIO port: 0xffffefff. This 32-bit word will implicitly turn motor 2 off (on/off/unchanged/undefined/?).
d. To check if sensor 1 is giving a valid data I have to read bit 13 from address 0xFF200060 and test if the bit has the value 0.
e. To read the current value of sensor 1, I have to read bits 27 to 30 from address 0xFF200060.
5. Answer the following questions about the Timer:
a. Does the timer count up or down? Count down
b. How do you initialize the timer’s period? Set the periodl (base +8) and periodh
(base+12) to a certain value. The timer then counts down from the period on a
100MHz clock
base+8 R/W Periodl – lower 16 bits of Timeout period
base+12 R/W Periodh – upper 16 bits of Timeout period
c. How can you check if the timer has completed its period?
Continuously poll the timeout bit (base+0) (1 if timer has timed out – write 0 to this address to clear)
d. Suppose the processor executes one instruction every clock cycle, and you start the timer at cycle 7, as shown in the table below. At what time does the next instruction execute?
Time (cycles) Instruction
1 movia r3, 0xff202000
3 movi r2, 10000
4 stwio r2, 8(r3)
5 stwio r0, 12(r3) # 10000 cycle period
6 movi r2, 4
7 stwio r2, 4(r3) # Start timer
??? ldwio r2, 0(r3)
Could be cycle 8? [Or Cycle 10007, which corresponds to around 0.1 ms at 100Mhz]
6. Write the timer delay subroutine to be used in Part 2. This must be a proper subroutine that follows the NIOS II ABI
# DELAY Subroutine
# counts down a period of N on a 100MHz clock speed. Returns when done.
# Takes in arguments: r4 = N
DELAY: # lets use caller saved registers since its only a callee. r8-r15 movia r8, 0xFF202000 # r7 contains the base address for the timer
stwio r0, 0(r8) # clear timer
stwio r4, 8(r8) # set the period to be N clock cycles lower half srli r4, r4, 16 stwio r4, 12(r8) # set the period to be N clock cycles upper half movui r11, 4 stwio r11, 4(r8) # start the timer without continuing or interrupts POLL:
ldwio r10, 0(r8) # load potential time out bit andi r10, r10, 0x1 # isolate bit 1
movia r12, 0x1 beq r12, r10, TIMEOUT # is timer == 1? if it is then we have timed out br POLL TIMEOUT:
Ret
7. Write a simple test program that uses your timer subroutine to blink an LED with a period of 1 second. (Recall: Red LEDs are at location ff200000)
.global _start
_start:
movia sp, 0x17fff80 # Initialise stack pointer movia r8, 0x0 # Initialise LED value at r8
movia r7, 0xff200000 # Initialise red LED address at r7
LOOP:
movia r4, 100000000 PRE: # Counts down a period of 1 second at 100mhz
addi sp, sp, -4 # size of stack frame
stw ra, 0(sp) # store ra
stw r8, 4(sp) call DELAY POST: # store r8
ldw ra, 0(sp) ldw r8, 4(sp) # recover regs
addi sp, sp, 4 # remove stack frame
movia r9, 0x1 # xor mask
xor r8, r8, r9 # not operation on bit 1 of r8
stwio r8, 0(r7) # write to led on -> off, off -> on
br LOOP # go again
# DELAY Subroutine
# counts down a period of N on a 100MHz clock speed. Returns when done.
# Takes in arguments: r4 = N
DELAY: # lets use caller saved registers since its only a callee. r8-r15 movia r8, 0xFF202000 # r7 contains the base address for the timer
stwio r0, 0(r8) # clear timer
stwio r4, 8(r8) # set the period to be N clock cycles lower half srli r4, r4, 16 stwio r4, 12(r8)) # set the period to be N clock cycles upper half movui r11, 4 stwio r11, 4(r8) # start the timer without continuing or interrupts POLL:
ldwio r10, 0(r8) # load potential time out bit andi r10, r10, 0x1 # isolate bit 1
movia r12, 0x1 beq r12, r10, TIMEOUT # is timer == 1? if it is then we have timed out br POLL TIMEOUT:
ret
8. Write the assembly language programs for part 1 and part 2 described above. Your code must be well commented. Compile your code using the Altera Monitor program and fix any compilation errors.
Part 1 program:
In 1 loop:
Read both sensors, calculate tilt, turn motor accordingly
[s1 motor0 s2]
if s1 > s2, turn motor ccw if s1 < s2, turn motor cw
Duty cycle = on/(on+off)
On+off = 524300
Solve for on and off:

On = 524300*dutycycle%, off = 524300*(1-dutycycle%)
Part 2 program:
.equ ADDR_JP1, 0xFF200060 # Address GPIO JP1
.equ STACK_BEGIN, 0x17fff80 # Address of initial stack
.equ THRESHOLD, 1 # minimum difference between the sensors for the motor to turn on
.equ NEG_THRESHOLD, -1 # minimum difference between the sensors for the motor to turn on
.equ DUTY_CYCLE_TOT, 5243 # total number of duty cycles/100, on+off at
100MHz, 524300 in example
.equ DUTY_CYCLE, 50 # % out of 100 .equ DUTY_CYCLE_C, 50 # 1-DUTY_CYCLE%
.global _start _start:
/* Important register usage:
R4 passing argument N into delay subroutine
R8 address of GPIO, unchanged throughout
R9 varying use, sensor 1 value, then direction of motor rotation
R10 varying use, sensor 2 value
R11 varying use, written to DR register to turn on motor and set direction
R12 ON duty cycles number
R13 OFF duty cycles number
R14 varying use, for calculating duty cycles, then stores negative threshold
R15 stores threshold */ movia sp, STACK_BEGIN # Initialise stack pointer LOOP:
movia r8, ADDR_JP1 # Initialise GPIO address at r8
movia r9, 0x07f557ff # set direction registers to motor output sensor input
stwio r9, 4(r8) # put in DIR
movia r14, DUTY_CYCLE_TOT # total duty cycle mul r12, r14, DUTY_CYCLE # number of cycles on mul r13, r14, DUTY_CYCLE_C # number of cycles off movia r14, NEG_THRESHOLD # -threshold movia r15, THRESHOLD # threshold # LOOP:
SENSOR1: # read sensor 1 and put in r9 movia r9, 0xffffefff # enable sensor 1, disable all motors stwio r9, 0(r8) ldwio r9, 0(r8) # checking for valid data sensor 1 srli r10, r9, 13 # is valid if bit 13 == 0 for sensor 1 andi r10, r10, 0x1
bne r0, r10, SENSOR1 # wait for valid bit to be low: sensor 3 needs to be valid
srli r9, r9, 27 # shift to the right by 27 bits so that 4-bit sensor value is in lower 4 bits
andi r9, r9, 0x0f # mask
SENSOR2: # read sensor 2 and put in r10 movia r10, 0xffffbfff # enable sensor 2, disable all motors stwio r10, 0(r8) ldwio r10, 0(r8) # checking for valid data sensor 2 srli r11, r10, 15 # bit 15 is valid bit for sensor 2
andi r11, r11,0x1
bne r0, r11, SENSOR2 # wait for valid bit to be low: sensor 2 needs to be valid
srli r10, r10, 27 # shift to the right by 27 bits so that 4-bit sensor value is in lower 4 bits
andi r10, r10, 0x0f # mask
CALCULATE: # Calculate direction of motor rotation, store ‘10’ in r9 if cw, ‘00’ if ccw.
sub r9, r9, r10 #r9-r10 bgt r9 , r15, ABOVETHRESHOLD blt r9, r14, ABOVETHRESHOLD # difference < -threshold BELOWTHRESHOLD:
Movia r9, 0x01 # motor off br MOTORON ABOVETHRESHOLD: Blt r9, r0, RIGHT # r9-r10<0, r10>r9 LEFT:
Movia r9, 0x10 r9<=r10 br MOTORON
RIGHT: # r9<r10
Movia r9, 0x00
MOTORON:
movia r11, 0xfffffffc # motor0 enabled (bit0=0), direction set to forward (bit1=0) Add r11, r11, r9 # make use of calculation stwio r11, 0(r8)# turn motor on add r4, r0, r12 # ON duty cycles into parameter N
PRE: # duty cycles need to be saved in pre and recovered in post addi sp, sp, -4
stw ra, 0(sp) # store ra
stw r13, 4(sp) # store number of off duty cycles
call DELAY POST:
ldw ra, 0(sp) # recover regs ldw r13, 4(sp) # store number of off duty cycles
addi sp, sp, 4 MOTOROFF:
movia r4, r13 # number of off duty cycles PRE2:
stw ra, 0(sp) # store ra
call DELAY POST2:
ldw ra, 0(sp) # recover regs
movia r12, 0xffffffff # motor0 disabled (bit0=1)
stwio r12, 0(r8)# turn motor off
br LOOP # go again
# DELAY Subroutine
# counts down a period of N on a 100MHz clock speed. Returns when done.
# Takes in arguments: r4 = N
DELAY: # lets use caller saved registers since its only a callee. r8-r15 movia r8, 0xFF202000 # r7 contains the base address for the timer
stwio r0, 0(r8) # clear timer
stwio r4, 8(r8) # set the period to be N clock cycles lower half srli r4, r4, 16 stwio r4, 12(r8)) # set the period to be N clock cycles upper half movui r11, 4 stwio r11, 4(r8) # start the timer without continuing or interrupts POLL:
ldwio r10, 0(r8) # load potential time out bit andi r10, r10, 0x1 # isolate bit 1
movia r12, 0x1 beq r12, r10, TIMEOUT # is timer == 1? if it is then we have timed out br POLL TIMEOUT:
ret