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Diff: dn_hdlc.c

Revision:

0:d3f5fdf2e6da

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dn_hdlc.c	Thu Sep 01 14:53:55 2016 +0000
@@ -0,0 +1,253 @@
+/*
+Copyright (c) 2014, Dust Networks. All rights reserved.
+
+HDLC library.
+
+\license See attached DN_LICENSE.txt.
+*/
+
+#include "dn_hdlc.h"
+#include "dn_uart.h"
+#include "dn_lock.h"
+
+//=========================== variables =======================================
+
+typedef struct {
+   // admin
+   dn_hdlc_rxFrame_cbt  rxFrame_cb;
+   // input
+   uint8_t              lastRxByte;
+   bool                 busyReceiving;
+   bool                 inputEscaping;
+   uint16_t             inputCrc;
+   uint8_t              inputBufFill;
+   uint8_t              inputBuf[DN_HDLC_INPUT_BUFFER_SIZE];
+   // output
+   uint16_t             outputCrc;
+} dn_hdlc_vars_t;
+
+dn_hdlc_vars_t dn_hdlc_vars;
+
+//=========================== prototypes ======================================
+
+// callback handlers
+void dn_hdlc_rxByte(uint8_t rxbyte);
+// input
+void dn_hdlc_inputOpen();
+void dn_hdlc_inputWrite(uint8_t b);
+void dn_hdlc_inputClose();
+// helpers
+uint16_t dn_hdlc_crcIteration(uint16_t crc, uint8_t data_byte);
+
+//=========================== public ==========================================
+
+/**
+\brief Setting up the instance.
+*/
+void dn_hdlc_init(dn_hdlc_rxFrame_cbt rxFrame_cb) {
+   // reset local variables
+   memset(&dn_hdlc_vars,   0, sizeof(dn_hdlc_vars));
+   
+   // store params
+   dn_hdlc_vars.rxFrame_cb = rxFrame_cb;
+   
+   // initialize UART
+   dn_uart_init(dn_hdlc_rxByte);
+}
+
+//=========================== private =========================================
+
+//===== callback_handler
+
+/**
+\brief Function which getted called each time a byte is received over UART.
+
+\param[in] rxbyte The received byte.
+*/
+void dn_hdlc_rxByte(uint8_t rxbyte) {
+   
+   // lock the module
+   dn_lock();
+   
+   if        (
+         dn_hdlc_vars.busyReceiving==FALSE  &&
+         dn_hdlc_vars.lastRxByte==DN_HDLC_FLAG &&
+         rxbyte!=DN_HDLC_FLAG
+      ) {
+      // start of frame
+      
+      // I'm now receiving
+      dn_hdlc_vars.busyReceiving       = TRUE;
+      
+      // create the HDLC frame
+      dn_hdlc_inputOpen();
+      
+      // add the byte just received
+      dn_hdlc_inputWrite(rxbyte);
+   } else if (
+         dn_hdlc_vars.busyReceiving==TRUE   &&
+         rxbyte!=DN_HDLC_FLAG
+      ){
+      // middle of frame
+      
+      // add the byte just received
+      dn_hdlc_inputWrite(rxbyte);
+      
+      if (dn_hdlc_vars.inputBufFill+1>DN_HDLC_INPUT_BUFFER_SIZE) {
+         // input buffer overflow
+         dn_hdlc_vars.inputBufFill       = 0;
+         dn_hdlc_vars.busyReceiving      = FALSE;
+      }
+   } else if (
+         dn_hdlc_vars.busyReceiving==TRUE   &&
+         rxbyte==DN_HDLC_FLAG
+      ) {
+      // end of frame
+      
+      // finalize the HDLC frame
+      dn_hdlc_inputClose();
+      
+      if (dn_hdlc_vars.inputBufFill==0) {
+         // invalid HDLC frame
+      } else {
+         // hand over frame to upper layer
+         dn_hdlc_vars.rxFrame_cb(&dn_hdlc_vars.inputBuf[0],dn_hdlc_vars.inputBufFill);
+         
+         // clear inputBuffer
+         dn_hdlc_vars.inputBufFill=0;
+      }
+      
+      dn_hdlc_vars.busyReceiving = FALSE;
+   }
+   
+   dn_hdlc_vars.lastRxByte = rxbyte;
+   
+   // unlock the module
+   dn_unlock();
+}
+
+//===== output
+
+/**
+\brief Start an HDLC frame in the output buffer.
+*/
+void dn_hdlc_outputOpen() {
+   // initialize the value of the CRC
+   dn_hdlc_vars.outputCrc = DN_HDLC_CRCINIT;
+   
+   // send opening HDLC flag
+   dn_uart_txByte(DN_HDLC_FLAG);
+}
+
+/**
+\brief Add a byte to the outgoing HDLC frame being built.
+
+\param[in] b The byte to add.
+*/
+void dn_hdlc_outputWrite(uint8_t b) {
+   
+   // iterate through CRC calculator
+   dn_hdlc_vars.outputCrc = dn_hdlc_crcIteration(dn_hdlc_vars.outputCrc,b);
+   
+   // write optional escape byte
+   if (b==DN_HDLC_FLAG || b==DN_HDLC_ESCAPE) {
+      dn_uart_txByte(DN_HDLC_ESCAPE);
+      b = b^DN_HDLC_ESCAPE_MASK;
+   }
+   
+   // data byte
+   dn_uart_txByte(b);
+}
+
+/**
+\brief Finalize the outgoing HDLC frame.
+*/
+void dn_hdlc_outputClose() {
+   uint16_t   finalCrc;
+   
+   // finalize the calculation of the CRC
+   finalCrc   = ~dn_hdlc_vars.outputCrc;
+   
+   // write the CRC value
+   dn_hdlc_outputWrite((finalCrc>>0)&0xff);
+   dn_hdlc_outputWrite((finalCrc>>8)&0xff);
+   
+   // write closing HDLC flag
+   dn_uart_txByte(DN_HDLC_FLAG);
+   
+   // flush the UART
+   dn_uart_txFlush();
+}
+
+//===== input
+
+/**
+\brief Start an HDLC frame in the input buffer.
+*/
+void dn_hdlc_inputOpen() {
+   // reset the input buffer index
+   dn_hdlc_vars.inputBufFill = 0;
+   
+   // initialize the value of the CRC
+   dn_hdlc_vars.inputCrc = DN_HDLC_CRCINIT;
+}
+
+/**
+\brief Add a byte to the incoming HDLC frame.
+
+\param[in] b The byte to add.
+*/
+void dn_hdlc_inputWrite(uint8_t b) {
+   if (b==DN_HDLC_ESCAPE) {
+      dn_hdlc_vars.inputEscaping = TRUE;
+   } else {
+      if (dn_hdlc_vars.inputEscaping==TRUE) {
+         b = b^DN_HDLC_ESCAPE_MASK;
+         dn_hdlc_vars.inputEscaping = FALSE;
+      }
+      
+      // add byte to input buffer
+      dn_hdlc_vars.inputBuf[dn_hdlc_vars.inputBufFill] = b;
+      dn_hdlc_vars.inputBufFill++;
+      
+      // iterate through CRC calculator
+      dn_hdlc_vars.inputCrc = dn_hdlc_crcIteration(dn_hdlc_vars.inputCrc,b);
+   }
+}
+
+/**
+\brief Finalize the incoming HDLC frame.
+*/
+void dn_hdlc_inputClose() {
+   
+   // verify the validity of the frame
+   if (dn_hdlc_vars.inputCrc==DN_HDLC_CRCGOOD) {
+      // the CRC is correct
+      
+      // remove the CRC from the input buffer
+      dn_hdlc_vars.inputBufFill    -= 2;
+   } else {
+      // the CRC is incorrect
+      
+      // drop the incoming fram
+      dn_hdlc_vars.inputBufFill     = 0;
+   }
+   
+   // reset escaping
+   dn_hdlc_vars.inputEscaping = FALSE;
+}
+
+//=========================== helpers =========================================
+
+/**
+\brief Perform a single CRC iteration.
+
+\param[in] crc The current running CRC value.
+\param[in] b   The new byte.
+
+\return The updated CRC running value.
+*/
+uint16_t dn_hdlc_crcIteration(uint16_t crc, uint8_t b) {
+   return (crc >> 8) ^ dn_hdlc_fcstab[(crc ^ b) & 0xff];
+}
+