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copied!<p>$sx registers are guaranteed to be unchanged accross function calls, so its the callee (sum function) the responsible of saving them, only if its going to change their value.</p> <p>$tx registers, on the other hand, are not guaranteed to be unchanged over function calls, so its the responsability of the caller (vbsme) to save them.</p> <p>You should save $sx in the callee stack.</p> <p>So when you start coding the sum function, you should save space in the stack If you want to save n registers, then save n*4.</p> <p>Space in the stack is saved by subtracting on the $sp register, which points to the base of the stack. Before your function code, you should create the stack for that function, saving all caller-saved registers, return address and global pointer registers when neccesary</p> <pre><code>sum: #stack frame creation. Caller registers saved, # return address and frame pointer subu $sp,$sp,36 #Save space in the stack for registers $s0, $s7 + $ra sw $ra,32($sp) sw $s0,0($sp) sw $s1,4($sp) #and so on. Note that also you should save the $ra register only if you are # going to call another function #do something with $sx #stack frame destruction #restore $sx and $ra registers lw $ra,32($sp) lw $s0,0($sp) lw $s1,4($sp) ... lw $s7,28($sp) jr $ra </code></pre> <p>By the way, by convention, registers $a0, $a3 should keep the arguments to the function you are calling. Also, note that because you are using the $s0, $s7 registers, you have to do some extra work. Convention says that if you don't use them, then you shouldn't save them, so maybe you could use the $tx (temporary) registers instead.</p>

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