root / trunk / bootloader / rs485_sw.c @ 184
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| 1 | /**
|
|---|---|
| 2 | * @file rs485_sw.c |
| 3 | * @brief RS485 implementation using UART hardware module and no interrupts |
| 4 | * |
| 5 | * This uses the AVR's UART hardware module but does polling rather than |
| 6 | * interrupts to handle transmission and receiving. It assumes the use |
| 7 | * of an external UART<->RS485 converter with the RXEN and TXEN pins tied |
| 8 | * together. |
| 9 | * |
| 10 | * @author Kevin Woo <kwoo@2ndt.com> |
| 11 | **/ |
| 12 | |
| 13 | /**
|
| 14 | * @brief Initializes the uart |
| 15 | * @param baud The baudrate. Use the definitions in rs485_sw.h |
| 16 | */ |
| 17 | void rs485_init(uint16_t baud) {
|
| 18 | // Set baud rate
|
| 19 | UBRRH = (uint8_t)(baud>>8);
|
| 20 | UBRRL = (uint8_t)baud; |
| 21 | |
| 22 | // Enable RX/TX
|
| 23 | UCSRB = _BV(RXEN) | _BV(TXEN); |
| 24 | |
| 25 | // Enable the TXEN pin as output
|
| 26 | DDRD |= TX_EN; |
| 27 | rs485_toggle_transmit(RS485_TX_OFF); |
| 28 | } |
| 29 | |
| 30 | /**
|
| 31 | * @brief Non-blocking receive |
| 32 | * |
| 33 | * Receives a byte from the UART if one exists. If none exist the function |
| 34 | * will return an error code immediately. If there is a byte to receive, |
| 35 | * it will be placed in a passed in pointer and return. |
| 36 | * |
| 37 | * @pre The RS485 TXEN line is not enabled |
| 38 | * @param output_byte Byte to store the received message |
| 39 | * @return 0 on success, negative if there is nothing to receive |
| 40 | */ |
| 41 | int8_t rs485_get_byte(uint8_t *output_byte) {
|
| 42 | if (UCSRA & _BV(RXC)) {
|
| 43 | *output_byte = UDR; |
| 44 | return 0; |
| 45 | } else {
|
| 46 | return -1; |
| 47 | } |
| 48 | } |
| 49 | |
| 50 | /**
|
| 51 | * @brief Blocking send |
| 52 | * |
| 53 | * Sends the byte in data onto the network. The function will block until |
| 54 | * the transmit is complete so that the transmit enable line can be toggled |
| 55 | * safely. It will wait until any current transmission completes before sending |
| 56 | * and will wait until it completes before returning. The RS485 TX enable line |
| 57 | * is automatically toggled by the function and should not be done so |
| 58 | * outside the function. |
| 59 | * |
| 60 | * @param data The byte to send |
| 61 | */ |
| 62 | void rs485_send_byte(uint8_t data) {
|
| 63 | //Waits until current transmit is done
|
| 64 | while (!(UCSRA & _BV(UDRE)));
|
| 65 | |
| 66 | // Enable writes and send
|
| 67 | rs485_toggle_transmit(RS485_TX_ON); |
| 68 | UDR = data; |
| 69 | |
| 70 | // Waits until the transmit is done
|
| 71 | while(!(UCSRA & _BV(TXC)));
|
| 72 | rs485_toggle_transmit(RS485_TX_OFF); |
| 73 | UCSRA |= _BV(TXC); |
| 74 | |
| 75 | return;
|
| 76 | } |
| 77 | |
| 78 | /**
|
| 79 | * @brief Toggles the RS485 TXEN line |
| 80 | * |
| 81 | * This function should not be used outside of this file |
| 82 | * |
| 83 | * @param state Whether to turn the pin on or off |
| 84 | */ |
| 85 | void rs485_toggle_transmit(uint8_t state) {
|
| 86 | if (state == RS485_TX_ON) {
|
| 87 | PORTD |= TX_EN; |
| 88 | } else {
|
| 89 | PORTD &= ~TX_EN; |
| 90 | } |
| 91 | } |