MCF5374 PCI->XLB->FLEXBUS aligned transfers hang the core?

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MCF5374 PCI->XLB->FLEXBUS aligned transfers hang the core?

nop head
I have ported a previously working USB host EHCI driver from an MCF5373 with an internal USB host to an MCF5474 with an NXP ISP1564 HS USB PCI Host controller on the PCI bus. The USB controller is a PCI bus master and it initiates transfers over the PCI bus, which then accesses the Flex bus via the XLB bus.

During the setup phase 8 byte command packets are sent and these are located in a 32 bit wide SRAM on a chip select. If the command is not on an 8 byte boundary then it works as expected. If the transfer is on an 8 byte boundary then the CPU seems to halt. If I hit break in my debugger then the PC is on the first instruction of my XLB interrupt handler. If I hit run then the interrupt handler runs and reports a bus error at the address of my command packet. It indicates that it is an 8 byte burst transfer on the XLB.

If I make the XLB timeout very big, e.g. 8191, clocks then I don't get a bus timeout but the processor still gets stuck. When I hit break it is always on the first instruction of an unrelated DMA interrupt handler. If I run then the USB transaction completes successfully and the processor halts at the next one, and so on.

Note the debugger is not having to do a force TA, it is simply asserting BKPT and waiting for FREEZE.

I can't see how this is anything other than a bug in the CPU. What state can the CPU be in where it is not processing instructions but it will respond to BKPT?





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