remove redundant CLB command,
update program3 using fixes from program2
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36e5abab60
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@ -82,7 +82,6 @@ tap_init: LDI #d64
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main_loop: LDI lfsr_routine // load address for the lfsr_routine label
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JAL r0 // jump to the lfsr_routine label
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LDW r11 // load the next ciphertext byte
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CLB r0 // clear leading bit because we do not expect errors
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XOR r7 // bitwise XOR the current state with ciphertext space to generate plaintext
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CLB r0 // clear the leading bit of the plaintext as in requirements
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STW r12 // store plaintext to write pointer
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@ -1,5 +1,5 @@
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// Program 3 register use map:
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// r0 is the accumulator, r1 and r2 is often used to cache temp values
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// Program 2 register use map:
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// r0 is the accumulator, r1 is often used to cache temp values
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// r5 is the TAP LUT link register
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// r6 is LFSR tap pattern
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// r7 is LFSR state value
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@ -34,20 +34,20 @@ tap_init: LDI #d64
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PUT r11 // set read pointer to 64
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LDI #d0
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PUT r12 // set write pointer to 0
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LDI #d10
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PUT r8 // load 10 into preamble counter
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LDI #d9
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PUT r8 // load 9 into preamble counter
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LDI #d64
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PUT r9 // load 64 (total encryption length) to r9
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LDI done
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NXT r10 // decrement tap selection by 1, starts at 9 for the first iteration
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JEZ r0 // if no more taps left that didn't work, raise the done flag
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LDI tap_init
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LDI lut_return
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PUT r5 // put the tap_loop address in r5
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LDI tap_lut
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ADD r10
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ADD r10 // add 2*tap select to tap_lut location, results in location of selected tap pattern
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JMP r0 // jump to LUT, which loads the tap pattern into r0
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PUT r6 // tap pattern now in r6
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lut_return: PUT r6 // tap pattern now in r6
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LDW r11 // get the first preamble character
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PUT r1 // put cipher text into r1
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LDI #d32 // load expected space character
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@ -59,13 +59,14 @@ tap_init: LDI #d64
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NXT r9 // decrement total encryption chars remaining
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tap_loop: LDI lfsr_routine
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JAL r0 // jump to lfsr routine which calculates next state in r7
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LDI #d0 // load space char expected plaintext
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LDI #d32 // load space char expected plaintext
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XOR r7
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CLB r0 // clear leading bit in the expected ciphertext
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PUT r1 // store expected cipher text in r1
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LDI tap_init
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PUT r2 // load the outer loop top into r2
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LDW r11 // load actual ciphertext
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CLB r0 // clear leading bit for r0 since we do not expect any errors for this program
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SUB r1 // subtract actual from expected, result of 0 means matching
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JNZ r2 // jump to outer loop (picks new tap pattern) if the actual cipher was not equal to the expected
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LDI #d32 // load preamble char
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@ -78,21 +79,22 @@ tap_init: LDI #d64
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JEZ r0 // if r8 (preamble counter) is zero, then all preamble have matched and current tap pattern is correct, jump to main loop
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LDI tap_loop
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JMP r0 // jump to tap_loop if characters matched but preamble is not over
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main_loop: LDI correct
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main_loop: LDI lfsr_routine // load address for the lfsr_routine label
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JAL r0 // jump to the lfsr_routine label
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LDI correct
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PUT r1 // put correct handle address in r1
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LDW r11 // load the next ciphertext byte
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CHK r0 // check ciphertext for error
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JEZ r1 // if no error, jump to correct, otherwise continue to error handling
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JEZ r1 // if no error goto correct handler, otherwise continue to error handler
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error: LDI #x80 // load error flag character into r0
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STW r12 // store error flag to write pointer
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LDI common
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JMP r0 // jump out of error handling, to common operations after writing
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correct: XOR r7 // bitwise XOR the current state with ciphertext space to generate plaintext
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correct: CLB r0 // clear leading bit because we do not expect errors
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XOR r7 // bitwise XOR the current state with ciphertext space to generate plaintext
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CLB r0 // clear the leading bit of the plaintext as in requirements
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STW r12 // store plaintext to write pointer
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common: LDI lfsr_routine // load address for the lfsr_routine label
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JAL r0 // jump to the lfsr_routine label
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NXT r11 // increment read pointer
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common: NXT r11 // increment read pointer
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NXT r12 // increment write pointer
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LDI done // load address of label done
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NXT r9 // decrement number of remaining plaintext chars
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