Introduction

Comm library is meant for structured communication implementation on host and client sides. It doesn't provide any specific communication interface implementation. It is a way to design it. Read about the background on accompanying post (it has pretty pictures).

Details

Library assumes query - response master - slave communication.

First implementation is made in C due to targeting embedded devices. Two major sets of functions are important: * CommStack_X functions * CommInterface_X functions

Functions have "this pointer" style for first parameter. C++ wrapper is possible and planed.

CommStack interface

This set of functions is called from application to communicate data. It's implemented in library. Library then calls CommInterface_X functions. For single instance of comm interface an object of type SCommStack must exist which is placed as "this pointer" parameter to CommStack_X functions.

``` struct _SCommStack; typedef struct _SCommStack SCommStack;

typedef SCommStack * HCOMMSTACK;

struct _SCommStack { SCommLayer *m_psCommLayer; ///< Pointer to array of comm layers. Lowest layer (physical) at index 0. COMMCOUNT m_cntNumberOfLayers; ///< Number of layers in array. unsigned char m_byFlags; ///< Of ECommStackFlags. unsigned char m_byLastError; }; ```

Object is initialized in CommStack_Init call. Comm layers get connected in this call - after successful return stack is ready for communication.

``` HCOMMSTACK CommStack_Init(unsigned char byFlags, SCommStack * psCommStack, SCommLayer *psCommLayers, COMMCOUNT cntLayerCount); void CommStack_PacketStart(HCOMMSTACK hCommStack); void CommStack_Send(HCOMMSTACK hCommStack, const unsigned char *pbyData, COMMCOUNT cntByteCount); void CommStack_PacketEnd(HCOMMSTACK hCommStack); ECommStatus CommStack_TransmitProcess(HCOMMSTACK hCommStack); ECommStatus CommStack_ReceiveProcess(HCOMMSTACK hCommStack, COMMCOUNT *pcntNumBytes, unsigned char **ppbyReceivedData); COMMCOUNT CommStack_GetBufferSize(HCOMMSTACK hCommStack); void CommStack_Disconnect(HCOMMSTACK hCommStack);

```

CommLayer interface

This set of functions is not called directly from application. Interface is meant to be implemented for each communication type, e.g. serial. SCommLayer type object represents single layer. ``` struct _SCommLayer; typedef struct _SCommLayer SCommLayer;

struct _SCommLayer { void *m_pLayerInstance; ///< "THIS" pointer. const ICommLayer *m_piCommLayer; ///< Pointer to comm interface implementation. SCommLayer *m_psUpperLayer; ///< Pointer to upper comm layer. SCommLayer *m_psLowerLayer; ///< Pointer to lower comm layer. HCOMMSTACK m_hCommStack; ///< Comm stack handle to which layer belongs. }; ``` Since C is not objective language the type extension in terms of deriving is faked with void *m_pLayerInstance member where implementation can store own type object. It must do so in custom init function together with providing an address of ICommLayer instance which holds function pointers to functions implementing that layer.

``` static void myCommLayer_Init(SCommLayer *psCommLayer) { SMyCommLayerType *psThis = (SMyCommLayerType *)psCommLayer->m_pLayerInstance; psThis->m_dwReceivedByteCount= 0; psThis->m_dwSendByteCount = 0; }

static COMMCOUNT myCommLayer_CommGetBufferSize(SCommLayer *psCommLayer, COMMCOUNT cntLowerLayerBufferSize) { SMyCommLayerType *psThis = (SMyCommLayerType *)psCommLayer->m_pLayerInstance; return psThis->m_dwBufferSizeInBytes; }

static void myCommLayer_PacketStart(SCommLayer *psCommLayer) { SMyCommLayerType *psThis = (SMyCommLayerType *)psCommLayer->m_pLayerInstance; // impl // . // . // . }

// other impl functions // . // . // .

static const ICommLayer sc_iMyCommLayerImpl = { COMM_EVENT_NULL, // ClientInit myCommLayer_HostInit, // HostInit myCommLayer_CommGetBufferSize, // CommGetBufferSize myCommLayer_PacketStart, // PacketStart myCommLayer_Send, // Send // pointers to other impl functions // . // . // . };

void MyCommLayer_Init(SCommLayer *psCommLayer, SMyCommLayerType *psMyCommLayerInstance, void * pBuffer, unsigned long dwBufferSizeInBytes) { psCommLayer->m_pLayerInstance = psMyCommLayerInstance; psCommLayer->m_piCommLayer = &sc_iMyCommLayerImpl; psMyCommLayerInstance->m_pbyBuffer = pBuffer; psMyCommLayerInstance->m_dwBufferSizeInBytes = dwBufferSizeInBytes; } ```