Minor fixes from code review. (#25)

Author: xchrishawk

src/main/application/intf_port.c

@@ -132,10 +132,11 @@ void intf_port_tick( tick_t tick )
 
 void intf_port_usart_rx( void )
 {
+    s_rx_tick = sys_get_tick();
+
     while( rx_buf_avail() != 0 &&
            usart_rx( INTF_PORT_USART, s_rx_buf + s_rx_count, 1 ) )
     {
-        s_rx_tick = sys_get_tick();
         s_rx_count++;
         evaluate_rx_buf();
     }
@@ -190,6 +191,13 @@ static void evaluate_rx_buf( void )
             return;
         }
     }
+    else if( header->crc != 0 )
+    {
+        // Enforce a CRC of zero for zero-sized packets
+        send_empty_packet( INTF_MESSAGE_REPLY_INVALID_CRC );
+        s_rx_count = 0;
+        return;
+    }
 
     // CRC check passed - process the packet then reset the buffer
     process_message( header, s_rx_buf + sizeof( intf_header_t ) );

src/main/drivers/eeprom.c

@@ -301,10 +301,11 @@ static void strobe_write_enable( void )
 {
     // The write to EEPE must happen within 4 clock cycles of the write to EEMPE.
     // Clear interrupt flag while writing bits to prevent this from being interrupted.
+    bool intrpt_en = sys_intrpt_enabled();
     sys_cli();
     set_bit( EECR, EEMPE );     // enable writes
     set_bit( EECR, EEPE );      // command write
-    sys_sei();
+    sys_set_intrpt_enabled( intrpt_en );
 
 }   /* strobe_write_enable() */