Started lab notes for labs 3 and 4.
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**/*.log
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**/*.synctex.gz
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**/*.aux
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**/.vscode
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**/.vscode
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**/_minted*
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\documentclass[letterpaper]{article}
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\author{Jonathan Chan (15354146)}
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\title{PHYS 319\\Labs 3 and 4 Notes}
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\usepackage{fullpage}
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\usepackage{minted}
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%{\renewcommand\fcolorbox[4][]{\textcolor{red}{\strut#4}}
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\begin{document}
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\maketitle
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To compile the C programs to .asm and .elf, I've modified my Makefile as below.
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\begin{minted}{makefile}
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SOURCES = $(wildcard *.c)
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EXEC = $(patsubst %.c, %.elf, $(SOURCES))
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DEVICE = msp430g2553
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INSTALL_DIR=$(HOME)/ti/msp430_gcc
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GCC_DIR = $(INSTALL_DIR)/bin
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SUPPORT_FILE_DIRECTORY = $(INSTALL_DIR)/include
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CC = $(GCC_DIR)/msp430-elf-gcc
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GDB = $(GCC_DIR)/msp430-elf-gdb
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#O0 works, O1 works, O2 doesn't -Os works
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CFLAGS = -I $(SUPPORT_FILE_DIRECTORY) -mmcu=$(DEVICE) -Os -g
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LFLAGS = -L $(SUPPORT_FILE_DIRECTORY) -T $(DEVICE).ld
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all: prog1 prog2 adc pwm
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prog1: prog1.c
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$(CC) $(CFLAGS) $(LFLAGS) $? -o prog1.elf
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$(CC) $(CFLAGS) $(LFLAGS) $? -S -o prog1.asm
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prog2: prog2.c
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$(CC) $(CFLAGS) $(LFLAGS) $? -o prog2.elf
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$(CC) $(CFLAGS) $(LFLAGS) $? -S -o prog2.asm
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adc: adc.c
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$(CC) $(CFLAGS) $(LFLAGS) $? -o adc.elf
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$(CC) $(CFLAGS) $(LFLAGS) $? -S -o adc.asm
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pwm: pwm.c
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$(CC) $(CFLAGS) $(LFLAGS) $? -o pwm.elf
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$(CC) $(CFLAGS) $(LFLAGS) $? -S -o pwm.asm
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debug: all
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$(GDB) ${EXEC}
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clean:
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rm prog1.elf prog2.elf adc.elf pwm.elf prog1.asm prog2.asm adc.asm pwm.asm
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\end{minted}
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\section{Program 1}
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Compiling from C, the produced Assembly file has a \textit{lot} of extra code, and appears to have been optimized differently. Below is the relevant section of the compiled .asm with some comments comparing lines to last lab's prog1.asm code.
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\begin{minted}{gas}
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.LCFI0:
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.loc 1 21 0
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MOV.W #23168, &WDTCTL ; turn off watchdog
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.loc 1 22 0
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MOV.B #65, &P1DIR ; set output direction (P1.6 and P1.0 for LEDs)
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.loc 1 23 0
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MOV.B #1, &P1OUT ; set initial state (LED1 on)
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.LBB2:
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.loc 1 27 0
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MOV.W #-5536, R12 ; amount to decrement by (60000 shown as signed word)
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.L6:
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.LVL0:
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MOV.W R12, @R1 ; use R1 as working register to decrement (first loop)
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.L3:
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.loc 1 28 0
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MOV.W @R1, R13 ; use R13 as working register for this loop
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CMP.W #0, R13 { JEQ .L2 ; go to next countdown if this one has reached zero
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.loc 1 29 0
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ADD.W #-1, @R1 ; decrement counter
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BR #.L3 ; loop
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.L2:
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.LVL1:
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.loc 1 27 0
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MOV.W R12, @R1 ; reset R1 as working register to decrement (second loop)
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.L5:
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.loc 1 28 0
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MOV.W @R1, R13 ; use R13 as working register for this loop
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CMP.W #0, R13 { JEQ .L4 ; break if countdown has reached zero
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.loc 1 29 0
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ADD.W #-1, @R1 ; decrement counter
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BR #.L5 ; loop
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.L4:
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.LVL2:
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.LBE2:
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.loc 1 32 0 discriminator 1
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XOR.B #65, &P1OUT ; switch LEDs
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.loc 1 26 0 discriminator 1
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BR #.L6 ; loop from top of loops
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\end{minted}
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\newpage
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This was generated using the following C code that doubles the count and thus halves the blinking rate.
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\begin{minted}{c}
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#include <msp430.h>
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void main(void) {
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volatile unsigned int count;
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WDTCTL = WDTPW + WDTHOLD; // Stop WDT
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P1DIR = 0x41; // Set P1 output direction
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P1OUT = 0x01; // Set the output
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while (1) { // Loop forever
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for (volatile unsigned char i = 0; i < 2; i++) { // decrement by 60000 twice
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count = 60000;
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while (count != 0) {
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count--; // decrement
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}
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}
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P1OUT = P1OUT ^ 0x41; // bitwise xor the output with 0x41
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}
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}
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\end{minted}
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\section{Program 2}
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Below is the C code used to make the LEDs blink in the red--green--both--none pattern, using the same XOR trick described in the last lab notes.
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\begin{minted}{c}
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#include <msp430.h>
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volatile unsigned char stateChanger;
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void main(void) {
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WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
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P1DIR = 0xF7; // C does not have a convenient way of
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// representing numbers in binary; use hex instead
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P1OUT = 0x08; // LEDs off
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P1REN = 0x08; // enable resistor
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P1IE = 0x08; // Enable input at P1.3 as an interrupt
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stateChanger = 0x1; // 0x01 to toggle LED0; 0x40 to toggle LED1
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_BIS_SR (LPM4_bits + GIE); // Turn on interrupts and go into the lowest
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// power mode (the program stops here)
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// Notice the strange format of the function, it is an "intrinsic"
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// ie. not part of C; it is specific to this chipset
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}
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// Port 1 interrupt service routine
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void __attribute__ ((interrupt(PORT1_VECTOR))) PORT1_ISR(void) {
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P1OUT ^= stateChanger; // toggle the LEDS
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stateChanger ^= 0x40; // 0x01 -> 0x41 -> 0x01
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P1IFG &= ~0x08; // Clear P1.3 IFG. If you don't, it just happens again.
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}
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\end{minted}
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\section{Analogue to Digital Conversion}
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\section{Pulse Width Modulation}
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\section{LED Dimmer}
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\end{document}
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