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POUnsetting and resetting certain bits
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copied!<p>For a homework assignment in school, I need to use a MMIO LED display where each led is exactly 2 bits stored within a byte. For the assignment I need to "move" these LEDs up, down, left, and right. I also need to set the color (I will be using 0x40 for this). Here's my issue:</p> <p>When I click the "right" arrow to move the LED over 1 column, it remains in the current column when it should be returning to black (0x00). If I click right 4 times (moving over exactly 1 byte), I get another lit LED, leaving the original one there.</p> <p>Here is my MIPS code:</p> <pre><code>getLedPattern: move $t2, $s2 andi $t1, $t2, 0x3 #remainder of x / 4 is in $t0 sll $t0, $t2, 2 #x / 4 is in $t0 beq $t0, 0, case0 beq $t0, 1, case1 beq $t0, 2, case2 case3: andi $a0, 0xFFFFFFFC #insert $a1 into bits 0 and 1 of $a0 into $v0 or $v0, $a0, $a1 jr $ra case2: andi $a0, 0xFFFFFCFF #insert $a1 into bits 2 and 3 of $a0 into $v0 #srl $a1, $a1, 2 or $v0, $a0, $a1 jr $ra case1: andi $a0, 0xFFFCFFFF #insert $a1 into bits 4 and 5 of $a0 into $v0 #srl $a1, $a1, 4 or $v0, $a0, $a1 jr $ra case0: andi $a0, 0xFCFFFFFF #insert $a1 into bits 6 and 7 of $a0 into $v0 #srl $a1, $a1, 6 or $v0, $a0, $a1 jr $ra setLED: addi $sp, $sp, -20 sw $ra, 0($sp) sw $t0, 4($sp) sw $t1, 8($sp) sw $t2, 12($sp) sw $t3, 16($sp) move $t5, $a0 sll $t6, $a1, 5 # y*32 srl $t2, $a2, 2 # x/4 add $t5, $t5, $t6 add $t5, $t5, $t2 lb $a0, 0($t5) move $a1, $a3 jal getLedPattern sb $v0, 0($t5) move $s3, $t5 lw $ra, 0($sp) lw $t0, 4($sp) lw $t1, 8($sp) lw $t2, 12($sp) lw $t3, 16($sp) addi $sp, $sp, 20 jr $ra </code></pre> <p>The logic is that it starts out at at memory location 0xFFFFOOO8 (top left LED), moves down one row (+32 bytes) and over x columns (plus x*bits). However, I can't seem to unset the current LED and move it over one. Any help would be appreciated. I believe that my or in getLedPattern: is wrong, but not 100% sure.</p> <p>Hopefully, getting this correct I will be able to get this correct in a general sense (no LED display).</p>

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