copied part 4 example asm code into files

Author: spitford

part4/lsex1.s

@@ -0,0 +1,18 @@
+.data          /* the .data section is dynamically created and its addresses cannot be easily predicted */
+var1: .word 3  /* variable 1 in memory */
+var2: .word 4  /* variable 2 in memory */
+
+.text          /* start of the text (code) section */
+.global _start
+
+_start:
+   ldr r0, adr_var1  @ load the memory address of var1 via label adr_var1 into R0
+   ldr r1, adr_var2  @ load the memory address of var2 via label adr_var2 into R1
+   ldr r2, [r0]      @ load the value (0x03) at memory address found in R0 to register R2
+   str r2, [r1, #2]  @ address mode: offset. Store the value found in R2 (0x03) to the memory address found in R1 plus 2. Base register (R1) unmodified.
+   str r2, [r1, #4]! @ address mode: pre-indexed. Store the value found in R2 (0x03) to the memory address found in R1 plus 4. Base register (R1) modified: R1 = R1+4
+   ldr r3, [r1], #4  @ address mode: post-indexed. Load the value at memory address found in R1 to register R3. Base register (R1) modified: R1 = R1+4
+   bkpt
+
+adr_var1: .word var1 /* address to var1 stored here */
+adr_var2: .word var2 /* address to var2 stored here */

part4/lsex2.s

@@ -0,0 +1,18 @@
+.data          /* the .data section is dynamically created and its addresses cannot be easily predicted */
+var1: .word 3  /* variable 1 in memory */
+var2: .word 4  /* variable 2 in memory */
+
+.text          /* start of the text (code) section */
+.global _start
+
+_start:
+   ldr r0, adr_var1  @ load the memory address of var1 via label adr_var1 into R0
+   ldr r1, adr_var2  @ load the memory address of var2 via label adr_var2 into R1
+   ldr r2, [r0]      @ load the value (0x03) at memory address found in R0 to register R2
+   str r2, [r1, r2]  @ address mode: offset. Store the value found in R2 (0x03) to the memory address found in R1 with the offset R2 (0x03). Base register (R1) unmodified.
+   str r2, [r1, r2]! @ address mode: pre-indexed. Store the value found in R2 (0x03) to the memory address found in R1 with the offset R2 (0x03). Base register (R1) modified: R1 = R1+R2.
+   ldr r3, [r1], r2  @ address mode: post-indexed. Load the value at memory address found in R1 to register R3. Then modify base register: R1 = R1+R2.
+   bx lr 
+
+adr_var1: .word var1 /* address to var1 stored here */
+adr_var2: .word var2 /* address to var2 stored here */

part4/lsex3.s

@@ -0,0 +1,18 @@
+.data          /* the .data section is dynamically created and its addresses cannot be easily predicted */
+var1: .word 3  /* variable 1 in memory */
+var2: .word 4  /* variable 2 in memory */
+
+.text          /* start of the text (code) section */
+.global _start
+
+_start:
+   ldr r0, adr_var1         @ load the memory address of var1 via label adr_var1 into R0
+   ldr r1, adr_var2         @ load the memory address of var2 via label adr_var2 into R1
+   ldr r2, [r0]             @ load the value (0x03) at memory address found in R0 to register R2
+   str r2, [r1, r2, LSL#2]  @ address mode: offset. Store the value found in R2 (0x03) to the memory address found in R1 with the offset R2 left-shifted by 2. Base register (R1) unmodified.
+   str r2, [r1, r2, LSL#2]! @ address mode: pre-indexed. Store the value found in R2 (0x03) to the memory address found in R1 with the offset R2 left-shifted by 2. Base register modified: R1 = R1+R2<<2
+   ldr r3, [r1], r2, LSL#2  @ address mode: post-indexed. Load the value at memory address found in R1 to register R3. Base register (R1) modified: R1 = R1+R2<<2
+   bkpt
+
+adr_var1: .word var1 /* address to var1 stored here */
+adr_var2: .word var2 /* address to var2 stored here */