Allow unsetting the port_enable_disable bit in portsc

[Demindiro]

This is necessary to avoid disabling the port when clearing a change bit.

[toku-sa-n]

Thank you for the PR, but I think what you need is clear_port_enabled_disabled which clears the bit by writing 1 to it. The bit is RW1C, and writing 0 to it has no effect. Please refer to pages 370 for RW1C and 407 for the bit, the specification revision 1.2.

[Demindiro]

Thank you for the PR, but I think what you need is clear_port_enabled_disabled which clears the bit by writing 1 to it. The bit is RW1C, and writing 0 to it has no effect. Please refer to pages 370 for RW1C and 407 for the bit, the specification revision 1.2.

I'm trying to avoid writing a 1 as I don't want the port to be disabled.

For context, I unset the bit here

[toku-sa-n]

Thank you for the context. I may understand a bit. Is the problem as follows?

1. You read the PORTSC register whose Port Enabled/Disabled (PED) bit is 1 because the port is enabled.
2. You modify the value fetched from the register. The PED bit is still 1.
3. You write back the value to the register, but the port becomes disabled as the PED bit is 1, and writing 1 to the bit disables the port.

[Demindiro]

Yes

[toku-sa-n]

Thank you. I didn't notice the problem before. Because this problem is not the PED bit specific, could you instead add the set_0 method with the documentation explaining the situation, the difference between itself and the clear_* method, and how to use it to the rw1c_bit macro?

[Demindiro]

Superseded by #148