--- a/main.c	Tue May 22 21:32:52 2012 +0800
+++ b/main.c	Tue May 22 23:23:38 2012 +0800
@@ -60,6 +60,12 @@
 static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL,
         _FDEV_SETUP_WRITE);
 
+uint16_t crc_out;
+static FILE _crc_stdout = FDEV_SETUP_STREAM(uart_putchar, NULL,
+        _FDEV_SETUP_WRITE);
+// convenience
+static FILE *crc_stdout = &_crc_stdout;
+
 static uint16_t n_measurements;
 // stored as decidegrees
 static int16_t measurements[NUM_MEASUREMENTS][MAX_SENSORS];
@@ -180,62 +186,60 @@
 int 
 uart_putchar(char c, FILE *stream)
 {
-    // XXX should sleep in the loop for power.
+    // XXX could perhaps sleep in the loop for power.
     if (c == '\n')
     {
         loop_until_bit_is_set(UCSR0A, UDRE0);
-        UDR0 = '\r';;
+        UDR0 = '\r';
     }
     loop_until_bit_is_set(UCSR0A, UDRE0);
     UDR0 = c;
+    if (stream == crc_stdout)
+    {
+        crc_out = _crc_ccitt_update(crc_out, '\n');
+    }
     if (c == '\r')
     {
         loop_until_bit_is_set(UCSR0A, UDRE0);
-        UDR0 = '\n';;
+        UDR0 = '\n';
+        if (stream == crc_stdout)
+        {
+            crc_out = _crc_ccitt_update(crc_out, '\n');
+        }
     }
     return 0;
 }
 
 static void
-update_crc(uint16_t *crc, const void *data, uint8_t len)
-{
-    for (uint8_t i = 0; i < len; i++)
-    {
-        *crc = _crc_ccitt_update(*crc, ((const uint8_t*)data)[i]);
-    }
-}
-
-static void
 cmd_fetch()
 {
-    uint16_t crc = 0;
+    crc_out = 0;
     uint8_t n_sensors;
     eeprom_read(n_sensors, n_sensors);
 
-    printf_P(PSTR("Time %lu\n"), clock_epoch);
-    update_crc(&crc, &clock_epoch, sizeof(clock_epoch));
-    printf_P(PSTR("%d sensors\n"), n_measurements);
+    fprintf_P(crc_stdout, PSTR("START\n"));
+    fprintf_P(crc_stdout, PSTR("time=%lu\n"), clock_epoch);
+    fprintf_P(crc_stdout, PSTR("sensors=%d\n"), n_measurements);
     for (uint8_t s = 0; s < n_sensors; s++)
     {
         uint8_t id[ID_LEN];
-        printf_P(PSTR("%d : "), s);
+        fprintf_P(crc_stdout, PSTR("sensor_id%d="), s);
         eeprom_read_to(id, sensor_id[s], ID_LEN);
-        printhex(id, ID_LEN);
-        putchar('\n');
-        update_crc(&crc, id, ID_LEN);
+        printhex(id, ID_LEN, crc_stdout);
+        fputc('\n', crc_stdout);
     }
-    printf_P(PSTR("%d measurements\n"), n_measurements);
+    fprintf_P(crc_stdout, PSTR("measurements=%d\n"), n_measurements);
     for (uint16_t n = 0; n < n_measurements; n++)
     {
-        printf_P(PSTR("%3d :"), n);
+        fprintf_P(crc_stdout, PSTR("meas%3d="), n);
         for (uint8_t s = 0; s < n_sensors; s++)
         {
-            printf_P(PSTR(" %6d"), measurements[n][s]);
-            update_crc(&crc, &measurements[n][s], sizeof(measurements[n][s]));
+            fprintf_P(crc_stdout, PSTR(" %6d"), measurements[n][s]);
         }
-        putchar('\n');
+        fputc('\n', crc_stdout);
     }
-    printf_P(PSTR("CRC : %d\n"), crc);
+    fprintf_P(crc_stdout, PSTR("END\n"));
+    fprintf_P(stdout, PSTR("CRC=%d\n"), crc_out);
 }
 
 static void
@@ -338,7 +342,7 @@
         eeprom_write(n, n_sensors);
         sei();
         printf_P(PSTR("Added sensor %d : "), n);
-        printhex(id, ID_LEN);
+        printhex(id, ID_LEN, stdout);
         putchar('\n');
     }
     else
@@ -448,7 +452,7 @@
     }
 }
 
-ISR(INT0_vwct)
+ISR(INT0_vect)
 {
 	need_comms = 1;
 }

--- a/simple_ds18b20.c	Tue May 22 21:32:52 2012 +0800
+++ b/simple_ds18b20.c	Tue May 22 23:23:38 2012 +0800
@@ -126,7 +126,7 @@
 }
 
 static void 
-printhex_nibble(const unsigned char b)
+printhex_nibble(const unsigned char b, FILE *stream)
 {
 	unsigned char  c = b & 0x0f;
 	if ( c > 9 ) { 
@@ -135,26 +135,26 @@
 	else {
 		c += '0';
 	}
-	putchar(c);
+	fputc(c, stream);
 }
 
 void 
-printhex_byte( const unsigned char  b )
+printhex_byte(const unsigned char b, FILE *stream)
 {
-	printhex_nibble( b >> 4 );
-	printhex_nibble( b );
+	printhex_nibble( b >> 4, stream);
+	printhex_nibble( b, stream);
 }
 
 void
-printhex(uint8_t *id, uint8_t n)
+printhex(uint8_t *id, uint8_t n, FILE *stream)
 {
 	for (uint8_t i = 0; i < n; i++)
 	{
 		if (i > 0)
 		{
-			putchar(' ');
+			fputc(' ', stream);
 		}
-		printhex_byte(id[i]);
+		printhex_byte(id[i], stream);
 	}
 }
 
@@ -190,7 +190,7 @@
 		{
 			printf_P(PSTR("CRC fail"));
 		}
-		printhex(id, OW_ROMCODE_SIZE);
+		printhex(id, OW_ROMCODE_SIZE, stdout);
 		printf_P(PSTR(" %d.%d ºC\n"), decicelsius/10, decicelsius % 10);
 	}
 	printf_P(PSTR("Done sensors\n"));

--- a/simple_ds18b20.h	Tue May 22 21:32:52 2012 +0800
+++ b/simple_ds18b20.h	Tue May 22 23:23:38 2012 +0800
@@ -1,12 +1,13 @@
 #ifndef SIMPLE_DS18B20_H_
 #define SIMPLE_DS18B20_H_
 #include <stdint.h>
+#include <stdio.h>
 
 #include "ds18x20.h"
 
 uint8_t simple_ds18b20_start_meas(uint8_t id[]);
-void printhex(uint8_t *id, uint8_t n);
-void printhex_byte( const unsigned char  b );
+void printhex(uint8_t *id, uint8_t n, FILE *stream);
+void printhex_byte( const unsigned char  b, FILE *stream );
 uint8_t simple_ds18b20_read_decicelsius( uint8_t id[], int16_t *decicelsius );
 uint8_t simple_ds18b20_read_all();