[umarcor]

uint32_t mask = (1 << size) - 1; is undefined if size==32. It produces 0x0.

This PR avoids masking the reg_val when the size of the field is 32.

Before:

$ sudo /opt/OFL/bin/openFPGALoader -c ft231X --pins=RXD:RTS:TXD:CTS --read-register CTRL1
Jtag probe limited to 3MHz
Jtag frequency : requested 6000000Hz -> real 3000000Hz
ret 0
Register raw value: 0x1e3d0
Reserved        0x0

After:

$ sudo /opt/OFL/bin/openFPGALoader -c ft231X --pins=RXD:RTS:TXD:CTS --read-register CTRL1
Jtag probe limited to 3MHz
Jtag frequency : requested 6000000Hz -> real 3000000Hz
ret 0
Register raw value: 0x1e3d0
Reserved        0x1e3d0

[trabucayre]

Good catch!
Thanks @umarcor !