From 17d5ca3b58ac743175a8cb54faecb18cd4451457 Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Fri, 22 May 2015 22:17:31 +0200
Subject: [PATCH] Clock handling factored out to a separate file.

---
 firmware/Makefile   |  2 +-
 firmware/clock.c    |  9 +++++++++
 firmware/clock.h    |  9 +++++++++
 firmware/firmware.c | 14 ++++++++------
 firmware/modbus.c   |  7 +++----
 5 files changed, 30 insertions(+), 11 deletions(-)
 create mode 100755 firmware/clock.c
 create mode 100644 firmware/clock.h

diff --git a/firmware/Makefile b/firmware/Makefile
index 9cfa527..e0bd502 100644
--- a/firmware/Makefile
+++ b/firmware/Makefile
@@ -1,5 +1,5 @@
 PROGRAM=firmware
-SRC=firmware.c modbus.c
+SRC=firmware.c modbus.c clock.c
 OBJ=$(SRC:.c=.o)
 
 MCU=atmega328p
diff --git a/firmware/clock.c b/firmware/clock.c
new file mode 100755
index 0000000..b618222
--- /dev/null
+++ b/firmware/clock.c
@@ -0,0 +1,9 @@
+#include <avr/io.h>
+#include "clock.h"
+
+void init_clock()
+{
+	// use the 16-bit Timer/Counter1 with 1024x prescaling
+	TCCR1B = _BV(CS12)|_BV(CS10); // CLK/1024
+}
+
diff --git a/firmware/clock.h b/firmware/clock.h
new file mode 100644
index 0000000..ed6c1df
--- /dev/null
+++ b/firmware/clock.h
@@ -0,0 +1,9 @@
+#ifndef CLOCK_H__
+#define CLOCK_H__ 1
+
+typedef uint16_t clock_t;
+#define get_clock() (TCNT1)
+#define CLOCK_HZ	(F_CPU/1024)
+extern void init_clock();
+
+#endif /* !CLOCK_H__ */
diff --git a/firmware/firmware.c b/firmware/firmware.c
index 2019402..d70705d 100644
--- a/firmware/firmware.c
+++ b/firmware/firmware.c
@@ -2,9 +2,11 @@
 #include <avr/interrupt.h>
 #include <util/delay.h>
 #include <stdio.h>
+#include "clock.h"
 #include "modbus.h"
 
-#define TIMEOUT 0x2FF
+#define ECHO_TIMEOUT		(CLOCK_HZ/10)	// 10 ms
+#define MEASUREMENT_WAIT	(CLOCK_HZ/3)	// three triggers per second
 
 #define N_TRIGGERS 3
 #define N_SENSORS 12
@@ -48,13 +50,13 @@ static void do_measurement(unsigned char trig)
 
 	pull_trigger(trig);
 
-	starttime = TCNT1;
+	starttime = get_clock();
 
 	while (to_start || to_measure) {
 		uint8_t bits = 0;
-		uint16_t now = TCNT1;
+		uint16_t now = get_clock();
 
-		if (now-starttime >= TIMEOUT)
+		if (now-starttime >= ECHO_TIMEOUT)
 			break;
 
 		bits = get_pin(trig);
@@ -180,8 +182,8 @@ int main()
 		for (trig = 0; trig < N_TRIGGERS; trig++) {
 			uint16_t now;
 			do_measurement(trig);
-			now = TCNT1;
-			while (TCNT1-now < 200)
+			now = get_clock();
+			while (get_clock()-now < MEASUREMENT_WAIT)
 				modbus_poll();
 		}
 
diff --git a/firmware/modbus.c b/firmware/modbus.c
index a49bd87..0c238c2 100644
--- a/firmware/modbus.c
+++ b/firmware/modbus.c
@@ -11,6 +11,7 @@
 #include <util/atomic.h>
 #include <util/delay.h>
 
+#include "clock.h"
 #include "modbus.h"
 
 #define BUFSIZE 128	// must be a power of two
@@ -44,13 +45,11 @@ static uint8_t mb_unit_id;
 #define UBRR_VAL        ((F_CPU + 8UL * UART_BAUD) / (16UL*UART_BAUD) - 1)
 #define wait_one_byte()	_delay_us(10*1000000/UART_BAUD)
 
-#define get_clock()	(TCNT1)
-#define CLOCK_SPEED	(F_CPU/1024)
 /*
  * According to Wikipedia, it is indeed 28 bits = 3.5 bytes without
  * start- and stopbits.
  */
-#define TIMEOUT		(28*CLOCK_SPEED/UART_BAUD)
+#define REQ_TIMEOUT		(28*CLOCK_HZ/UART_BAUD)
 
 uint16_t hold_regs[MB_N_HOLD_REGS];
 
@@ -196,7 +195,7 @@ void modbus_poll()
 		if (rx_bytes == 0) // nothing received yet
 			return;
 
-		if (get_clock() - last_rx < TIMEOUT) // still receiving
+		if (get_clock() - last_rx < REQ_TIMEOUT) // still receiving
 			return;
 
 		if (rx_bytes < 4) { // too short
-- 
2.43.0