PXI Multi-Function DAQ Driver Development in QNX: Full Guide

Table of Contents

PXI Multi-Function DAQ Driver Development in QNX: Full Guide

This technical series details the development of a PXI-2010 multi-function data acquisition (DAQ) card driver under QNX 6.20. Using a three-level separation architecture, the approach maximizes code reuse from Linux drivers while delivering robust, POSIX-compliant real-time performance.

⚡ Introduction
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Background
QNX is a distributed, multi-tasking, and highly reliable real-time operating system widely used in telecommunications, aerospace, and industrial automation. Many PXI devices lack native QNX drivers, necessitating custom development.

Key Contribution:

PXI-2010 driver supporting 4-channel synchronous A/D and 2-channel synchronous D/A
Implements a three-level architecture for modular, reusable design

Benefits of QNX Resource Managers:

Run as user-level processes (avoiding kernel debugging)
Modular and flexible architecture
POSIX-compliant interface for client applications

🛠 QNX Resource Manager Principles
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Device Driver Mechanism
QNX’s microkernel separates drivers from the kernel. Resource Managers register a namespace with the Process Manager, which forwards client requests to the appropriate manager.

Resource Manager Layers:

Function Layer – Provides unified API functions
Message Reception Layer – Parses client messages
Message Dispatch Layer – Schedules message handling
Thread Management Layer – Manages internal threads

Core Initialization Example:

main(int argc, char **argv)
{
    resmgr_connect_funs_t connect_funs;
    iofunc_funcs_t io_funs;
    
    iofunc_funcs_init(_RESMGR_CONNECT_NFUNCS, &connect_funs,
                      _RESMGR_IO_NFUNCS, &io_funs);
    connect_funs.open = io_open;
}

Message Types:

Connect Messages: open()
I/O Messages: devctl(), read(), write()

🔌 PXI Bus System Architecture
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PXI Overview PXI extends CompactPCI (PICMG 2.0) with additional instrumentation signals for precise timing and high-speed data acquisition.

Performance:

33 MHz / 32-bit → 132 MB/s
66 MHz / 64-bit → 528 MB/s

Extended PXI Signals:

10 MHz Reference Clock
8-bit PXI Trigger Bus (multi-card sync)
Star Trigger
13-bit Local Bus

These features enable synchronized acquisition across multiple PXI cards.

💻 PXI Driver Implementation (Three-Level Architecture)
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The driver is divided into three layers to facilitate modularity and Linux code reuse.

4.1 Application-Level Driver
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User-facing API functions for multi-channel A/D & D/A, multi-card synchronization, and auto-calibration.

Multi-Card Sync Example:

I16 D2K_SSI_SourceConn(U16 wCardNumber, U16 sigCode)
{
    DAS_IOT_SSI iotSSI;
    memset(&iotSSI, '\0', sizeof(DAS_IOT_SSI));
    iotSSI.wSigCode = sigCode;
    iotSSI.wDir = 1;
    
    if (devctl(CurrentCard.hDevDriver, DAS_IOC_SSI_CTL,
               &iotSSI, sizeof(iotSSI), NULL) < 0)
        return iotSSI.wErrorCode;
    
    return NoError;
}

4.2 System Call Level (Resource Manager)
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Central POSIX interface handling client requests via io_open(), io_devctl(), and io_close().

Key Data Structure:

typedef struct _iofunc_ocb {
    IOFUNC_ATTR_T *attr;
    int32_t ioflag;
    off_t offset;
    uint16_t sflag;
    uint16_t flags;
} iofunc_ocb_t;

io_devctl() Implementation:

int io_devctl(resmgr_context_t *ctp, io_devctl_t *msg, RESMGR_OCB_T *ocb)
{
    switch(msg->i.dcmd) {
        case DAS_IOC_SSI_CTL:        break;
        case DAS_IOC_AIO_CONFIG:     break;
        case DAS_IOC_SIMU_AI_PIO:    break;
        default: return DAS_ERR_NO_FUNCTION;
    }
    return _RESMGR_PTR(ctp, &msg->o, sizeof(msg->o) + nbytes);
}