SPI-Core crashes python kernel / linux kernel when access register_map

[TRnhld]

• PYNQ version: 3.0.1
• Board name: MicroZed 7020 (AES-Z7MB-7Z020)
• Pull request type: bug fix
• Description:
  • I've got a desigh with AXI Quad SPI (V3.2) Core. with following Configuration
    • Performance Mode = Disabled
    • Mode = Quad
    • No. of Slaves = 1
    • Slave Device = Spansion
    • FIFO Depth = 16 (also tried 256)
    • STARTUP Primitive = disabled
  • after loading the Overlay and accessing the IP's register_map, the python kernel crashes

o = Overlay(r'overlay/design7.xsa')
o.qspi_master_hier.axi_quad_spi.register_map

• Locating error-source
  • tracking the error in the pynq libraris i noticed, the registers ger acessed when calling *.register_map
  • the AXI Quad SPI-IP seems to have the has a special behaviour when accessing an empty RX-FIFO SPI DRR - causing timeout on AXI when FIFO is empty
  • the call for accessing this address happens in __init__-function of class pynq.registers.RegisterMap

based on this I created some sample code to see where the python kernel crashes:

from pynq import Overlay
o = Overlay(r'overlay/design7.xsa')
rs = pynq.registers.RegisterMap.create_subclass(o.qspi_master_hier.axi_quad_spi._register_name, o.qspi_master_hier.axi_quad_spi._registers)(o.qspi_master_hier.axi_quad_spi.mmio.array)
buf = o.qspi_master_hier.axi_quad_spi.mmio.array

array32 = buf.view(dtype='u4')

array32[0x10] = 0xa # resetting spi core

for k, v in rs._register_classes.items():
    index = v[1] // 4
    print("%02X "  % (v[1]//4), end='')

sleep(1)
print("\n")

for k, v in rs._register_classes.items():
    index = v[1] // 4
    if index == 0x1B:
        continue
    print("%02X "  % (v[1]//4), end='')
    sleep(0.1)
    array = array32[index:index+1]
    print("= %02X" % array[0])
    
sleep(1)
print("\n")

for k, v in rs._register_classes.items():
    index = v[1] // 4
    print("%02X "  % (v[1]//4), end='')
    sleep(0.1)
    array = array32[index:index+1] # axi bus gets timeout when trying to excess empty rx fifo
    print("= %02X" % array[0])

Output:

18 19 10 18 19 1C 1D 1E 07 1A 1B 08 0A 

18 = 180
19 = AD
10 = 00
18 = 180
19 = AD
1C = 01
1D = 00
1E = 00
07 = 00
1A = 00
08 = 400
0A = 00


18 = 180
19 = AD
10 = 00
18 = 180
19 = AD
1C = 01
1D = 00
1E = 00
07 # *Python kernel Restarts here*

• Additional tries and findings
  • I also did an implementation with same settings of AXI Quad SPI accept putting the core into performance mode
    • Note: having to do some other "going around bugs" - See here
    • here, the core gets accessed by mmap - library
    • in class pynq.pl_server.embedded_device.EmbeddedDevice the function mmap() will be called.
      • the line 599 array = np.frombuffer(mem, np.uint32, length >> 2, virt_offset) will cause the whole linux kernel to crash.