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fix program2

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This commit is contained in:
Arthur Lu
2022-08-17 19:01:43 -07:00
parent 9a8c9a3771
commit 570bd3698a
3 changed files with 19 additions and 16 deletions
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18
firmware/program2.asm
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@@ -34,20 +34,20 @@ tap_init: LDI #d64
PUT r11 // set read pointer to 64
LDI #d0
PUT r12 // set write pointer to 0
LDI #d10
PUT r8 // load 10 into preamble counter
LDI #d9
PUT r8 // load 9 into preamble counter
LDI #d64
PUT r9 // load 64 (total encryption length) to r9
LDI done
NXT r10 // decrement tap selection by 1, starts at 9 for the first iteration
JEZ r0 // if no more taps left that didn't work, raise the done flag
LDI tap_init
LDI lut_return
PUT r5 // put the tap_loop address in r5
LDI tap_lut
ADD r10
ADD r10 // add 2*tap select to tap_lut location, results in location of selected tap pattern
JMP r0 // jump to LUT, which loads the tap pattern into r0
PUT r6 // tap pattern now in r6
lut_return: PUT r6 // tap pattern now in r6
LDW r11 // get the first preamble character
PUT r1 // put cipher text into r1
LDI #d32 // load expected space character
@@ -59,13 +59,14 @@ tap_init: LDI #d64
NXT r9 // decrement total encryption chars remaining
tap_loop: LDI lfsr_routine
JAL r0 // jump to lfsr routine which calculates next state in r7
LDI #d0 // load space char expected plaintext
LDI #d32 // load space char expected plaintext
XOR r7
CLB r0 // clear leading bit in the expected ciphertext
PUT r1 // store expected cipher text in r1
LDI tap_init
PUT r2 // load the outer loop top into r2
LDW r11 // load actual ciphertext
CLB r0 // clear leading bit for r0 since we do not expect any errors for this program
SUB r1 // subtract actual from expected, result of 0 means matching
JNZ r2 // jump to outer loop (picks new tap pattern) if the actual cipher was not equal to the expected
LDI #d32 // load preamble char
@@ -78,12 +79,13 @@ tap_init: LDI #d64
JEZ r0 // if r8 (preamble counter) is zero, then all preamble have matched and current tap pattern is correct, jump to main loop
LDI tap_loop
JMP r0 // jump to tap_loop if characters matched but preamble is not over
main_loop: LDW r11 // load the next ciphertext byte
main_loop: LDI lfsr_routine // load address for the lfsr_routine label
JAL r0 // jump to the lfsr_routine label
LDW r11 // load the next ciphertext byte
CLB r0 // clear leading bit because we do not expect errors
XOR r7 // bitwise XOR the current state with ciphertext space to generate plaintext
CLB r0 // clear the leading bit of the plaintext as in requirements
STW r12 // store plaintext to write pointer
LDI lfsr_routine // load address for the lfsr_routine label
JAL r0 // jump to the lfsr_routine label
NXT r11 // increment read pointer
NXT r12 // increment write pointer
LDI done // load address of label done