PEXOR Linux device driver and DABC integration

A device driver has been developed to apply the PEXOR hardware for Linux OS. It is realized as a char driver kernel module, currently for kernel versions 2.6.27. The driver operations for read() and write() implement PIO to the PEXOR on-board memory. Operation mmap() allocates kernel buffers for DMA operations and maps these to user space addresses. The pexor kernel module manages these buffers with internal pools. Initiating a DMA transfer, retrieving and releasing DMA buffers is handled from user space by ioctl() operations. The gosip protocol [2] for communication between PEXOR and frontend devices via the SFP connections was integrated to the kernel module. Thus a user program does not need to apply this protocol explicitly, as for the previous LynxOS driver, but calls higher level ioctl() operations to access the SFP slaves. Besides, register i/o to the full address space of the board’s PCIe memory is also available by ioctl(). Hence it is also possible to apply this driver for another FPGA configuration of the PEXOR, e.g. to utilize a different protocol. The driver features a shared interrupt handler which is provided for data trigger interrupts from an attached TRIXOR trigger module. Handling of a “DMA is complete” interrupt which may be used with future versions of the PEXOR firmware is also prepared: the received DMA buffers are managed by a “bottom half” interrupt tasklet. This function is also used in the non-interrupt mode, although here it is invoked directly after polling for a bit of the DMA status register. Finally, the kernel module exports some internal information, such as register contents and numbers of DMA buffers, to sysfs for user inspection.