Due to this, I need to use python memoryview.cast('I') to access a FPGA avoiding double read/write strobe. No panic, you wont need an FPGA to answer the question below...
So here comes a python sample which fails ('testfile' can be any file here -just longer than 20 bytes-, but for me, eventually it will be a IO mapped FPGA HW):
#!/usr/bin/python
import struct
import mmap
with open('testfile', "r+b") as f:
mm=memoryview(mmap.mmap(f.fileno(), 20)).cast('I')
# now try to assign the 2 first U32 of the file new values 1 and 2
# mm[0]=1; mm[1]=2 would work, but the following fails:
mm[0:1]=memoryview(struct.pack('II',1,2)).cast('I') #assignement error
The error is:
./test.py
Traceback (most recent call last):
File "./test.py", line 8, in <module>
mm[0:1]=memoryview(struct.pack('II',1,2)).cast('I')
ValueError: memoryview assignment: lvalue and rvalue have different structures
I don't undestand the error... what "different structures" are we talking about??
How can I rewrite the right hand-side of the assignment expression so it works?? Changing the left-hand-side will fail for the FPGA... as it seems anything else generates wrong signal towards the hardware...
More generally, how should I rework my array of 32 bit integers to fit the left-hand-side of the assignment...?
