CMPE$-250$

Assembly and Embedded Programming

Fall $2024$

Homework Three

This problem explores two strategies for accessing the elements of an array to implement the

following loop expression, where R$0$ refers to the CPU register R$0,$ R$1$ refers to the CPU

register R$1,$ and Array is an array of byte values allocated in memory.

$R0=0$

for $=(R1=0$;$R1<mn>1</mn><mn>0</mn><mn>0</mn>$;$R1++)$

$R=R0+$ Array$[R1]$

a$.$ Write an assembly language code fragment to implement the loop expression as follows.

Use a conditional branch instruction, $($i$.$e$.,$ Bcond$),$ for loop control.

Use indexed mode addressing to access the array: $[$RBase$,$ RIndex$].$

Use one register to hold the base, $($i$.$e$.,$ starting$),$ address of each array.

Use another register to hold the index of the element being accessed.

b$.$ Write an assembly language code fragment to implement the loop expression as follows.

Use a conditional branch instruction, $($i$.$e$.,$ Bcond$)$ for loop control.

Use displacement mode addressing to access the array, where the displacement is $0$

such that there is effectively register indirect mode addressing: $[$RIndirect$,$ #$0]$

Use one register to hold the address of the array element being accessed.

This problem explores two strategies for sequentially accessing the elements of a word array

to implement an assembly language subroutine Total according to these specifications.

Accepts a pointer to an array of signed words in register R$1.$

Accepts a word value in register R$2,$ which indicates the number of array elements.

Returns the total, $($i$.$e$.,$ sum$),$ of array elements in register RO$.$

On return, preserves contents of all registers, other than return result register and PSR$.$

a$.$ Write an assembly language subroutine to implement Total as follows.

Use displacement mode addressing to access each element: $[$R$1,$ #$0].$

Manually update the array pointer to access the next element: ADDS R$1,....$

Use a down counter to control iteration $($count from R$2$ down to $0).$

b$.$ Write an assembly language subroutine to implement Total as follows.

Use the autoincrement form of load multiple LDM to access each array element and

update the array pointer in one instruction.

Use a down counter to control iteration $($count from R$2$ down to $0).$