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Howdy, I am working on a port of the gen68302 BSP to my own 68302 based module. In reading through the initialization code I am having trouble seeing how interrupts are set in the vector table for a 68000 (ie NO_VBR). Does anyone actually have RTEMS running on a 68000 based processor? Overview: 1: I cannot explain why the vector number is multiplied by 6 and then 10 subtracted to get the address to store the ISR service routine. 2: How does ISR_Handler calculate the vector number to then use to call into the ISR dispatch table. Details: Basically I have followed where Install_clock from ckinit.c calls set_vector with the vector number of 137 (correct for timer 1), then ISR address and a 1 for RTEMS_TYPE (not RAW). set_vector( clock_isr, CLOCK_VECTOR, 1 ); set_vector in turn calls : rtems_interrupt_catch( handler, vector, (rtems_isr_entry *) &previous_isr ); rtems_interrupt_catch calls: _ISR_Install_vector (vector, (proc_ptr)new_isr_handler, (proc_ptr *)old_isr_handler ); This is really a call to _CPU_ISR_install vector in m68k\cpu.c. _CPU_ISR_install_vector then places the timer handler into the rtems interrupt dispatch table and loads the address of the common _ISR_Handler into the interrupt vector by calling: _CPU_ISR_install_raw_handler( vector, _ISR_Handler, &ignored ); In _CPU_ISR_install_raw_handler for the case where there is no VBR, the handler is stored at an address (vector*6-10). Why is the number *6-10??? Also in ISR_Handler, how is the vector number determined. From the code it looks like ISR_Handler (in the case of a 68000) is supposed to be called from a jump routine at the actual vector. Is this the case? I could not find anywhere where a dump jump routine was loaded at the actual vector location. If however that is the case then the stack does not look like it is cleaned up enough to allow the rte to work. Thanks for any help.... -Don ------ Don Post BlazeNet, Inc. firstname.lastname@example.org www.blaze-net.com Because IT should be Easy