Velleman I/O, specific error message when linked with dummy library

otherio/lib/rt/src/os_linux/rt_io_m_usb_agent.c

@@ -44,9 +44,14 @@ static pwr_tStatus IoAgentInit( io_tCtx ctx,
 
   sts = libusb_init( &local->libusb_ctx);
   if ( sts != 0) {
-    op->Status = sts;
+    if ( sts == io_cLibDummy)
+      op->Status = IO__DUMMYBUILD;
+    else
+      op->Status = IO__INITFAIL;
+      errh_Error( "Init of USB agent failed '%s', error status %d", ap->Name, sts);
+
     local->libusb_ctx = 0;
-    errh_Error( "Init of USB agent failed '%s'", ap->Name);
+    return op->Status;
   }
   else {
     op->Status = IO__SUCCESS;

otherio/lib/rt/src/os_linux/rt_io_m_velleman_k8055_board.c

@@ -86,10 +86,13 @@ static pwr_tStatus IoCardInit( io_tCtx ctx,
 
   sts = libusb_open( device, &local->libusb_device);
   if ( sts != 0) {
-    op->Status = IO__INITFAIL;
+    if ( sts == io_cLibDummy)
+      op->Status = IO__DUMMYBUILD;
+    else
+      op->Status = IO__INITFAIL;
     ((pwr_sClass_Velleman_K8055 *)rp->op)->Status = op->Status;
     local->libusb_device = 0;
-    return IO__INITFAIL;
+    return op->Status;
   }
 
   if ( libusb_kernel_driver_active( local->libusb_device, 0) != 0)

otherio/lib/usb_dummy/src/usb_dummy_functions.c

@@ -3,6 +3,7 @@
  */
 #include <sys/types.h>
 #include <stdint.h>
+#include "rt_io_base.h"
 
 struct libusb_context;
 struct libusb_device;
@@ -27,12 +28,12 @@ struct libusb_device_descriptor {
 	uint8_t  bNumConfigurations;
 };
 
-int libusb_init(libusb_context **ctx) {return 0;}
+int libusb_init(libusb_context **ctx) {return io_cLibDummy;}
 void libusb_exit(libusb_context *ctx) {}
 ssize_t libusb_get_device_list(libusb_context *ctx,
 			       libusb_device ***list) {return 0;}
 void libusb_free_device_list(libusb_device **list, int unref_devices) {}
-int libusb_open(libusb_device *dev, libusb_device_handle **handle) {return 0;}
+int libusb_open(libusb_device *dev, libusb_device_handle **handle) {return io_cLibDummy;}
 void libusb_close(libusb_device_handle *dev_handle) {}
 int libusb_interrupt_transfer(libusb_device_handle *dev_handle,
 			      unsigned char endpoint, unsigned char *data, int length,

src/lib/rt/src/rt_io_base.h

@@ -53,6 +53,8 @@ typedef struct io_sCtx *io_tCtx;
 #define NULL (void *) 0
 #endif
 
+
+#define io_cLibDummy -9999
 #define IO_CHANLIST_SIZE 250
 
 #define FIXOUT 2