Add driver to receive Phillips RC5 IR protocol

drivers/ir_rx5_rx.c

@@ -0,0 +1,151 @@
+/** @file   ir_rc5_rx.c
+    @author M. P. Hayes, UCECE
+    @date   21 May 2013
+    @brief  Infrared serial receiver driver for Phillips RC5 protocol.
+*/
+
+/* The Phillips RC-5 protocol uses the following format of 14 bits:
+   1 start bit
+   1 field bit (this used to be a second start bit)
+   1 toggle bit
+   5 address bits
+   6 command bits
+ 
+   Manchester encoding is used for the bits.  The start bit is a `1' bits.
+   `1' bits have the IR modulation on for the second half of the cycle.
+   `0' bits have the IR modulation on for the first half of the cycle.
+
+   Each bit period is 1778 microseconds (64 cycles of 36 kHz modulation)
+   thus a frame is 24.9 ms.
+
+   While a button is pressed, a frame is repeatedly sent.  If the button
+   is repressed, the toggle bit is changed.
+
+   This is a simple polled implementation that will block for the entire frame
+   if it detects a start bit.
+*/
+
+
+#include "ir_rc5_rx.h"
+#include "pio.h"
+#include "delay.h"
+
+#define IR_RC5_BIT_PERIOD_US 1778
+
+#ifndef IR_RC5_RX_ACTIVE_STATE
+/* Most IR demodulators have an active low output.  */
+#define IR_RC5_RX_ACTIVE_STATE 0
+#endif
+
+
+/** Return output state of IR receiver.
+    @return IR receiver state (1 = IR modulation detected).  */
+static inline uint8_t ir_rc5_rx_get (void)
+{
+    return pio_input_get (IR_RC5_RX_PIO) == IR_RC5_RX_ACTIVE_STATE;
+}
+
+
+uint8_t ir_rc5_rx_ready_p (void)
+{
+    return ir_rc5_rx_get ();
+}
+
+
+static uint16_t ir_rc5_rx_wait_state (uint8_t state)
+{
+    uint16_t us;
+    
+    for (us = 0; us < IR_RC5_BIT_PERIOD_US; us++)
+    {
+        if (ir_rc5_rx_get () == state)
+            return us;
+        /* TODO: figure out how to determine the fudge term.  Ideally,
+           we should poll a counter incremented by the CPU clock.  */
+        DELAY_US (1 - 0.4);
+    }
+    return us;
+}
+
+
+static uint16_t ir_rc5_rx_wait_transition (void)
+{
+    uint8_t initial;
+    
+    initial = ir_rc5_rx_get ();
+
+    return ir_rc5_rx_wait_state (!initial);
+}
+
+
+/** Receive RC5 data packet over IR serial link.  
+    @return 14-bits of data or error status code
+    @note No error checking is performed.  If there is no activity on the
+    IR serial link, this function returns immediately.  Otherwise, this
+    function blocks until the entire frame is received.  This must be called
+    frequently to ensure that a start bit is seen.  */
+int16_t ir_rc5_rx_read (void)
+{
+    int16_t data;
+    int i;
+    uint16_t us;
+
+    /* Look to see if there is some IR modulation marking the second
+       half of the first start bit.  It is possible that we may have
+       missed the start bit.  In this case we are likely to
+       time out.  */
+    if (!ir_rc5_rx_ready_p ())
+        return IR_RC5_RX_NONE;
+
+    /* The old RC-5 format had two start bits; this made a bit-bashed
+       software implementation easier.  The problem is that we have
+       been called just before the falling edge of the start bit.
+       So we have to special case these two bits.  */
+
+    /* Search for the next falling transition.  */
+    us = ir_rc5_rx_wait_state (0);
+    if (us >= IR_RC5_BIT_PERIOD_US)
+        return IR_RC5_RX_TIMEOUT;
+
+    if (us > (IR_RC5_BIT_PERIOD_US >> 1))
+    {
+        /* The field bit is 0.  */
+        data = 2;
+    }
+    else
+    {
+        /* The field bit is 1; so delay until middle of bit period.  */
+        data = 3;
+        us = ir_rc5_rx_wait_state (1);
+        if (us >= IR_RC5_BIT_PERIOD_US)
+            return IR_RC5_RX_TIMEOUT;
+    }
+
+    for (i = 2; i < 14; i++)
+    {
+        data <<= 1;
+        
+        DELAY_US (0.5 * IR_RC5_BIT_PERIOD_US + 100);
+
+        us = ir_rc5_rx_wait_transition ();
+        if (us >= IR_RC5_BIT_PERIOD_US)
+            return IR_RC5_RX_TIMEOUT;
+
+        if (ir_rc5_rx_get ())
+            data |= 1;
+    }
+
+    return data;
+}
+
+
+/** Initialise IR serial receiver driver.  */
+void ir_rc5_rx_init (void)
+{
+    /* Ensure PIO clock activated for reading.  */
+    pio_init (IR_RX_PIO);
+
+    /* Configure IR receiver PIO as input.  */
+    pio_config_set (IR_RX_PIO, PIO_INPUT);
+}
+

drivers/ir_rx5_rx.h

@@ -0,0 +1,34 @@
+/** @file   ir_rc5_rx.h
+    @author M. P. Hayes, UCECE
+    @date   21 May 2013
+    @brief  Infrared serial receiver driver for Phillips RC5 protocol.
+*/
+
+#ifndef IR_RC5_RX_H
+#define IR_RC5_RX_H
+
+#include "config.h"
+
+/** Status return codes.  */
+typedef enum ir_rc5_rx_ret 
+{
+    /** No data to read.  */
+    IR_RC5_RX_NONE = 0,
+    /** Timeout waiting for transition.  */
+    IR_RC5_RX_TIMEOUT = -1
+} ir_rc5_rx_ret_t;
+
+
+/** Receive RC5 data packet over IR serial link.  
+    @return 14-bits of data or error status code
+    @note No error checking is performed.  If there is no activity on the
+    IR serial link, this function returns immediately.  Otherwise, this
+    function blocks until the entire frame is received.  This must be called
+    frequently to ensure that a start bit is seen.  */
+int16_t ir_rc5_rx_read (void);
+
+
+/** Initialise IR serial receiver driver.  */
+void ir_rc5_rx_init (void);
+
+#endif