Let me propose a revised scheme for midas standard VME calls (mvmestd.h). 

Pierre mentioned some limitations before, and I find now also some fields 
to improve. Right now, the vme_open() call retrieves a handle. For some 
interfaces (like SBS/Bit3), one has to obtain separate handles for 
different addressing modes A24D32/A32D32 and so on, which I find a bit 
troublesome. I would rather keep the handle internally, invisible to the 
user, and use ioctl() statments to change the address/data mode. 

So the API could look like:

vme_open()       Deprecated, will be removed
vme_init(void)   Standard initialization, open device(s), stores handles
                 internally in a table
vme_exit(void)   Deallocates any memory, close handles

vme_read(void *dst, DWORD vme_addr, DWORD size)
vme_write(void *src, DWORD vme_addr, DWORD size)

vme_ioctl(int request, int *param)

                 Request is one of 
                   VME_IOCTL_CRATE_SET/GET
                     Sets VME crate (in case several interfaces are
                     plugged into singlePC, meaningless for embedded CPUs)
                   VME_IOCTL_DEST_SET/GET
                     VME_BUS/VME_RAM/VME_LM for VME bus, RAM in VME 
                     interface, or LM for local memory (used in Bit3 
                     interface)
                   VME_IOCTL_AMOD_SET/GET
                     Sets/Retrieves VME AMOD (= VME_AMOD_xxx as currently
                     defined in mvmestd.h)
                   VME_IOCTL_DSIZE_SET/GET
                     Sets/Retrieves VME data size (D8/D16/D32/D64)
                   VME_IOCTL_DMA_SET/GET
                     Enable/Disable DMA, should be independent of AMOD
                   VME_IOCTL_INTR_ATTACH/DETACH/ENABLE/DISABLE
                     Set VME interrupts
                   VME_IOCTL_AUTO_INCR_SET/GET
                     Set autoincremet of source pointer, can be disabled
                     for FIFO readout

vme_mmap(void **ptr, DWORD vme_addr, DWORD size)
vme_unmap(void *ptr, DWORD size)
                  Map/Unmap VME to local memory

vme_read2(void *dst, DWORD vme_addr, DWORD size, DWORD flags)
vme_write2(void *src, DWORD vme_addr, DWORD size, DWORD flags)
                 With these functions one can directly specify the flags
                 usually managed by vme_ioctl(). Usefule for applications
                 where the address modifier for example has to be
                 different in each read/write operation.  

Note that the vme_read/write functions do not have a VME handle any more, 
nor an address modifier. This is all accomplished with vme_ioctl() calls.

Please have a look at this proposal, compare it with what you do currently 
in VME, and let me know if we should add/modify something. I volunteer to 
implement the API for the SBS/Bit3 617 and the Struck SIS1100/3100 
interfaces, for VxWorks somebody at TRIUMF should take care.