Typical Errors Leading to Application Hangs - 2021.2 English

Vitis Unified Software Platform Documentation: Application Acceleration Development (UG1393)

Document ID
English (United States)
Release Date
2021.2 English

The user errors that typically create application hangs are listed below:

  • Read-before-write in 5.0+ target platforms causes a Memory Interface Generator error correction code (MIG ECC) error. This is typically a user error. For example, this error might occur when a kernel is expected to write 4 KB of data in DDR, but it produces only 1 KB of data, and then try to transfer the full 4 KB of data to the host. It can also happen if you supply a 1 KB buffer to a kernel, but the kernel tries to read 4 KB of data.
  • An ECC read-before-write error also occurs if no data has been written to a memory location as the last bitstream download which results in MIG initialization, but a read request is made for that same memory location. ECC errors stall the affected MIG because kernels are usually not able to handle this error. This can manifest in two different ways:
    1. The CU might hang or stall because it cannot handle this error while reading or writing to or from the affected MIG. The xbutil query shows that the CU is stuck in a BUSY state and is not making progress.
    2. The AXI Firewall might trip if a PCIe® DMA request is made to the affected MIG, because the DMA engine is unable to complete the request. AXI Firewall trips result in the Linux kernel driver killing all processes which have opened the device node with the SIGBUS signal. The xbutil query shows if an AXI Firewall has indeed tripped and includes a timestamp.
    If the above hang does not occur, the host code might not read back the correct data. This incorrect data is typically 0s and is located in the last part of the data. It is important to review the host code carefully. One common example is compression, where the size of the compressed data is not known up front, and an application might try to migrate more data to the host than was produced by the kernel.