From 90c683d1da90ec93372a0af9265818e668f50cbf Mon Sep 17 00:00:00 2001
From: Arthur Lu <learthurgo@gmail.com>
Date: Sun, 28 Aug 2022 00:13:43 +0000
Subject: [PATCH] update program3 with new testbench spec

---
 RTL/program3_tb.sv    |  8 ++++----
 firmware/program3.asm | 11 ++++++-----
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/RTL/program3_tb.sv b/RTL/program3_tb.sv
index f1b13ea..f9e891a 100644
--- a/RTL/program3_tb.sv
+++ b/RTL/program3_tb.sv
@@ -24,11 +24,11 @@ module program3_tb ()        ;
 //  53 characters in length
 // *** No more than 24 leading space characters, including preamble. ***
 //    string     str1 = 
-//  string     str1  = "Mr. Watson, come here. I want to see you.";     // sample program 1 input
+  string     str1  = "        A joke is a very serious thing.";     // sample program 1 input
 //  string     str1  = " Knowledge comes, but wisdom lingers.    ";   // alternative inputs
 //  string     str1  = "  01234546789abcdefghijklmnopqrstuvwxyz. ";   //   (make up your own,
 //  string     str1  = "      A joke is a very serious thing.";   // 	as well)
-  string     str1  = "          Ajok          ";   // 
+//  string     str1  = "          Ajok          ";   // 
 //	string     str1  = "@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@";
 //	string     str1  = "``@@```@@@````@@@@````@@@@@";
 //  string     str1  = " Knowledge comes, but wisdom lingers.    ";   // 
@@ -110,7 +110,7 @@ module program3_tb ()        ;
 //  testbench will change on falling clocks to avoid race conditions at rising clocks
     for (int i=0; i<64; i++) begin
       msg_crypto1[i]        = ((msg_padded1[i]-'h20) ^ lfsr1[i]);
-	  msg_crypto1[i][7]     = 0;//^msg_crypto1[i][6:0];       // prepend parity bit into MSB
+	  msg_crypto1[i][7]     = ^msg_crypto1[i][6:0];       // prepend parity bit into MSB
       $fdisplay(file_no,"i=%d, msg_pad=0x%h, lfsr=%b msg_crypt w/ parity = 0x%h",
          i,msg_padded1[i],lfsr1[i],msg_crypto1[i]);
 //for display purposes only, add 8'h20 to avoid nonprintable characters
@@ -135,7 +135,7 @@ module program3_tb ()        ;
       dut.DM.core[m+64] = msg_crypto1[m];
     for(int n=24; n<64; n++) begin	  	// load subsequent, possibly corrupt, encrypted message into data memory
 // set flipper = 8 or higher to disable bit corruption
-	  flipper = 8;//$random;                // value between 0 and 63, inclusive
+	  flipper = $random;//$random;                // value between 0 and 63, inclusive
       dut.DM.core[n+64] = msg_crypto1[n]^(1<<flipper);
       if(flipper<8) flipped[n]=1;
 	end
diff --git a/firmware/program3.asm b/firmware/program3.asm
index 13f2eb8..66a183a 100644
--- a/firmware/program3.asm
+++ b/firmware/program3.asm
@@ -1,5 +1,5 @@
 // Program 2 register use map:
-// r0 is the accumulator, r1 r2 r3 are often used to cache temp values
+// r0 is the accumulator, r1 is often used to cache temp values
 // r5 is the TAP LUT link register
 // r6 is LFSR tap pattern
 // r7 is LFSR state value
@@ -50,14 +50,14 @@ tap_init: LDI #d64
 	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
+	LDI #d0 // load expected space character
 	XOR r1 // get the initial state
 	PUT r7 // put initial state guess into r7
 	NXT r11 // increment read pointer
 	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 #d32 // load space char expected plaintext
+		LDI #d0 // load space char expected plaintext
 		XOR r7
 		CLB r0 // clear leading bit in the expected ciphertext
 		PUT r1 // store expected cipher text in r1
@@ -67,6 +67,7 @@ tap_init: LDI #d64
 		CLB r0 // clear leading bit for r0 since we do not expect any errors for this program
 		XOR r1 // XOR 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 #d0 // load preamble char
 		NXT r11 // increment read pointer
 		NXT r9 // decrement total encryption chars remaining
 		LDI finish_preamble // load main_loop location into r0
@@ -85,7 +86,7 @@ finish_preamble: LDI lfsr_routine
 	PUT r1 // put the plaintext in r1
 	LDI finish_preamble
 	PUT r2 // load address of finish_preamble loop into r2
-	LDI #d32 // get value of space
+	LDI #d0 // get value of space
 	XOR r1 // compare if r1 == 32
 	JEZ r2 // jump to finish preamble loop if this plaintext == space(32)
 	LDI correct_pre
@@ -94,7 +95,7 @@ finish_preamble: LDI lfsr_routine
 	JEZ r2
 	error_pre: LDI #x80
 		STW r12
-		LDI common
+		LDI common_pre
 		JMP r0
 	correct_pre: CLB r1
 		GET r1