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  1. Friedrich-Alexander-Universität
  2. Technische Fakultät
  3. Department Informatik
Friedrich-Alexander-Universität Lehrstuhl für Informatik 4 (Systemsoftware)
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                            SPiCboard

                            • libspicboard
                            com.h
                            Go to the documentation of this file.
                            1 #ifndef _COM_H
                            2 #define _COM_H
                            3 
                            4 #include <stdint.h>
                            5 #include <stddef.h>
                            6 #include "check.h"
                            7 
                            8 /**
                            9  * \addtogroup COM Serial Communication
                            10  *
                            11  * \brief Serial communication with SPiCboards
                            12  *
                            13  * \image html spicboard3_com_small.jpg
                            14  * The SPiCboard3 can perform serial communication using the three PINs
                            15  * on its upper right corner (\c TX at \c PD1, \c GND and \c RX at \c PD0 ).
                            16  * To establish a connection you have to connect its \c RX with \c TX of
                            17  * another board, both \c GND pins and \c TX with \c RX, like shown on the image
                            18  * above.
                            19  *
                            20  * For the transmission this library uses the transmission setting \c 8-E-1,
                            21  * in which we send (in addition to the start bit) 8 data bits,
                            22  * one even parity bit and one stop bit.
                            23  *
                            24  * Example: Transmission of the (decimal) value \c 23
                            25  * \image html com.png
                            26  * - \c PD0 is configured as input (\c RX)
                            27  * - \c PD1 is configured as output (\c TX)
                            28  * - The idle voltage is 5V, a logical high (this is a historic legacy from
                            29  * telegraphy, in which the line is held high to show that the line and
                            30  * transmitter are not damaged).
                            31  * - the transmission begins with the start bit, which changes the level from
                            32  * logical high (idle) to logical low.
                            33  * - the time interval \c T for transmitting one symbol is defined by the
                            34  * \c BAUD_RATE : \f$ T = \frac{1s}{BAUD\_RATE} \f$
                            35  * - the payload byte is sent bitwise, starting with the least significant bit
                            36  * - the parity bit ensures that an even number of logical highs has been sent
                            37  * (including parity - calculated using \c XOR ) - it can be used to detect
                            38  * transmission errors.
                            39  * - the stopbit finishes the transmission and leaves the line in a logical high
                            40  *
                            41  * \note The libspicboard implementation uses the 16bit <b>timer 4</b>.
                            42  *
                            43  * \note For educational purposes the transmission is implemented completely
                            44  * in software - for more advanced serial communcation you can use
                            45  * <a href="https://en.wikipedia.org/wiki/Universal_asynchronous_receiver-transmitter">USART</a>,
                            46  * described in Section 25 of the <a href="Atmel-42397-8-bit-AVR-Microcontroller-ATmega328PB_Datasheet.pdf">ATMega328PB Datasheet</a>.
                            47  *
                            48  * \sa COM_EXT
                            49  *
                            50  * @{
                            51  * \file com.h
                            52  * \version \$Rev: 15477 $
                            53  */
                            54 
                            55 #ifndef BAUD_RATE
                            56 /**
                            57  * \def BAUD_RATE
                            58  *
                            59  * Default baud rate (symbols per second) is 1200
                            60  */
                            61 #define BAUD_RATE 1200UL
                            62 #endif
                            63 
                            64 #if defined(__BUILTIN_AVR_DELAY_CYCLES)
                            65 /**
                            66  * \def sb_com_wait(FACTOR)
                            67  *
                            68  * Active wait loop for the transmission interval time \c T (determined by the baud rate) multiplied by \a FACTOR
                            69  */
                            70 #define sb_com_wait(FACTOR) __builtin_avr_delay_cycles((F_CPU*(FACTOR))/BAUD_RATE)
                            71 #else
                            72 #error Compiler does not support __builtin_avr_delay_cycles, which is required for sb_com_wait()
                            73 #endif
                            74 
                            75 // Error
                            76 /**
                            77  * \brief Error states used in mask
                            78  */
                            79 typedef enum {
                            80  ERROR_NO_STOP_BIT = 1, /**< no stop bit received */
                            81  ERROR_PARITY = 2, /**< parity bit wrong */
                            82  ERROR_BUFFER_FULL = 4, /**< receive buffer full */
                            83  ERROR_INVALID_POINTER = 8, /**< data pointer invalid */
                            84 } __attribute__ ((__packed__)) COM_ERROR_STATUS;
                            85 
                            86 CHECK_ENUM_SIZE(COM_ERROR_STATUS, 1)
                            87 /**
                            88  * \brief Send a single byte (8-bit) plus one start-, parity and stop bit
                            89  *
                            90  * \note Shall not be called inside a ISR!
                            91  *
                            92  * \param data the byte to send
                            93  */
                            94 void sb_com_sendByte(uint8_t data);
                            95 
                            96 /**
                            97  * \brief Receive one byte with start, parity and stop bit each
                            98  *
                            99  * We try to sample in the middle of each symbol, therefore we have to wait
                            100  * about \f$ 1.5T \f$ after receiving the start bit before reading the first
                            101  * data bit. Every subsequent symbol is sampled after a \f$ T \f$ delay.
                            102  *
                            103  * \image html com_recv.png
                            104  *
                            105  * Transmission errors are recorded and returned. They should not be ignored,
                            106  * because they usually indicate invalid data - there is no resend mechanism
                            107  * implemented in this library!
                            108  *
                            109  * \param data pointer to allocated space for the received byte
                            110  *
                            111  * \retval 0 no error
                            112  * \retval >0 bit mask describing the error:
                            113  * - 1. bit: no stop bit received (\c ERROR_NO_STOP_BIT )
                            114  * - 2. bit: parity bit wrong (\c ERROR_PARITY )
                            115  * - 3. bit: receive buffer full (\c ERROR_BUFFER_FULL )
                            116  * - 4. bit: data pointer invalid (\c ERROR_INVALID_POINTER )
                            117  */
                            118 uint8_t sb_com_receiveByte(uint8_t *data);
                            119 
                            120 
                            121 /** @}*/
                            122 
                            123 #endif
                            check.h
                            COM_ERROR_STATUS
                            COM_ERROR_STATUS
                            Error states used in mask.
                            Definition: com.h:79
                            sb_com_sendByte
                            void sb_com_sendByte(uint8_t data)
                            Send a single byte (8-bit) plus one start-, parity and stop bit.
                            sb_com_receiveByte
                            uint8_t sb_com_receiveByte(uint8_t *data)
                            Receive one byte with start, parity and stop bit each.
                            ERROR_PARITY
                            @ ERROR_PARITY
                            Definition: com.h:81
                            ERROR_BUFFER_FULL
                            @ ERROR_BUFFER_FULL
                            Definition: com.h:82
                            ERROR_INVALID_POINTER
                            @ ERROR_INVALID_POINTER
                            Definition: com.h:83
                            ERROR_NO_STOP_BIT
                            @ ERROR_NO_STOP_BIT
                            Definition: com.h:80
                            CHECK_ENUM_SIZE
                            #define CHECK_ENUM_SIZE(VAR, LEN)
                            Definition: check.h:71
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