From f36e0c51177979c57b3402676fe342c180f9cb5b Mon Sep 17 00:00:00 2001
From: Sadeep Madurange <sadeep@asciimx.com>
Date: Mon, 7 Apr 2025 18:09:48 +0800
Subject: Keygen using timer.

---
 lock/back.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 53 insertions(+), 9 deletions(-)

(limited to 'lock/back.c')

diff --git a/lock/back.c b/lock/back.c
index 9da6688..f373d20 100644
--- a/lock/back.c
+++ b/lock/back.c
@@ -3,6 +3,7 @@
 #include <stdint.h>
 #include <string.h>
 
+#include <avr/io.h>
 #include <avr/interrupt.h>
 #include <util/delay.h>
 
@@ -10,16 +11,30 @@
 #include "uart.h"
 #include "util.h"
 
-#define RX_PIN         PD7
-#define RX_DDR         DDRD
-#define RX_PORT        PORTD
-#define RX_PCIE        PCIE2
-#define RX_PCINT       PCINT23
-#define RX_PCMSK       PCMSK2
-#define RX_PCINTVEC    PCINT2_vect
+#define PWM_MIN      500
+#define PWM_MID      1500
+#define PWM_MAX      2500
+#define PWM_TOP      20000
+
+#define RX_PIN       PD7
+#define RX_DDR       DDRD
+#define RX_PORT      PORTD
+#define RX_PCIE      PCIE2
+#define RX_PCINT     PCINT23
+#define RX_PCMSK     PCMSK2
+#define RX_PCINTVEC  PCINT2_vect
+
+static char chars[] = {
+	'0', '8', '3', '6', 'a', 'Z', '$', '4', 'v', 'R', '@',
+	'E', '1', 'o', '#', ')', '2', '5', 'q', ';', '.', 'I',
+	'c', '7', '9', '*', 'L', 'V', '&', 'k', 'K', '!', 'm',
+	'N', '(', 'O', 'Q', 'A', '>', 'T', 't', '?', 'S', 'h',
+	'w', '/', 'n', 'W', 'l', 'M', 'e', 'H', 'j', 'g', '[',
+	'P', 'f', ':', 'B', ']', 'Y', '^', 'F', '%', 'C', 'x'
+};
 
-// todo: atomic var
 static volatile int rxdr = 0;
+static uint8_t charslen = sizeof(chars) / sizeof(chars[0]);
 
 static inline void await_reply(void)
 {
@@ -30,8 +45,32 @@ static inline void await_reply(void)
 		_delay_ms(100);
 }
 
+static inline void keygen(char *buf, uint8_t n)
+{
+	int i;
+	uint8_t sreg;
+	uint16_t idx; 
+	
+	sreg = SREG;
+	cli();
+	idx = TCNT1; 
+	SREG = sreg;
+
+	for (i = 0; i < n; i++, idx++)
+		buf[i] = chars[(idx % charslen)]  ;
+	buf[n - 1] = '\0';
+}
+
+static inline void timer_init(void)
+{
+	TCCR1A |= (1 << WGM11) | (1 << COM1A1);
+	TCCR1B |= (1 << WGM13) | (1 << CS11);
+	ICR1 = PWM_TOP; /* we use the same timer for servo's PWM */
+}
+
 int main(void)
 {
+	uint8_t n;
 	uint8_t rxaddr[ADDRLEN] = { 194, 178, 83 };
 	uint8_t txaddr[ADDRLEN] = { 194, 178, 82 };
 
@@ -45,6 +84,7 @@ int main(void)
 	RX_PCMSK |= (1 << RX_PCINT);
 
 	uart_init();
+	timer_init();
 	radio_init(rxaddr);
 	radio_print_config();
 
@@ -58,6 +98,10 @@ int main(void)
 			rxdr = 0;
 			xor(KEY, buf, msg, WDLEN);
 			if (strncmp(msg, SYN, WDLEN) == 0) {
+				keygen(key, WDLEN);
+				uart_write("DEBUG: session key = ");
+				uart_write_line(key);
+
 				xor(KEY, key, msg, WDLEN);
 				radio_sendto(txaddr, msg, WDLEN);
 				await_reply();
@@ -79,7 +123,7 @@ int main(void)
 				uart_write_line("ERROR: handshake failed");
 			}
 		} else {
-			uart_write_line("No IRQ");
+			uart_write_line("DEBUG: no new packets");
 			_delay_ms(2000);
 		}
 	}
-- 
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