read the memory mapped address - pcie - kernel hangs

Onur Atilla onurati at
Fri Jan 10 18:03:16 EST 2020

On 10.01.20 15:58, Muni Sekhar wrote:
> On Fri, Jan 10, 2020 at 4:46 PM Primoz Beltram <primoz.beltram at> wrote:
>> Hi,
>> Have read also other replays to this topic.
>> I have seen-debug such deadlock problems with FPGA based PCIe endpoint
>> devices (Xilinx chips) and usually (if not signal integrity problems),
>> the problem was in wrong AXI master/slave bus handling in FPGA design.
>> I guess you have FPGA Xilinx PCIe endpoint IP core attached as AXI
>> master to FPGA internal AXI bus (access to AXI slaves inside FPGA design).
>> If FPGA code in your design does not handle correctly AXI master
>> read/write requests, e.g. FPGA AXI slave does not generate bus ACK in
>> correct way, the PCIe bus will stay locked (no PCIe completion sent
>> back), resulting in complete system lock. Some PCIe root chips have
>> diagnostic LEDs to help decode PCIe problems.
>>  From your notice about doing two 32bit reads on 64bit CPU, I would
>> guess the problem is in handling AXI transfer size signals in FPGA slave
>> code.
>> I would suggest you to check the code in FPGA design. You can use FPGA
>> test bench simulation to check the behaviour of PCIe endpoint originated
>> AXI read/write requests.
>> Xilinx provides test bench simulation code for their PCIe IP's.
>> They provide also PCIe root port model, so you can simulate AXI
>> read/writes accesses as they would come from CPU I/O memory requests via
>> PCIe TLPs.
> Thank you so much for sharing valuable information, will work on this.
>> WBR Primoz


you may also want to have a look at the AXI Timeout Block (ATB) to
prevent system/core locks due to a missing ACK of a slave. If given by
the HW, ATB generates an alternative response in case the slave fails to
respond within a given time. It may also trigger an interrupt to help
handle/debug the error.


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