RP2350 datasheet doesn't describe some registers and clock sources

[duskwuff]

The following registers appear in the datasheet, but are not documented. Given the names, I assume they are used for testing, but a confirmation in the documentation (or details on what they do!) would be nice.

• DFTCLK_XOSC_CTRL
• DFTCLK_ROSC_CTRL
• DFTCLK_LPOSC_CTRL

The following sources are listed on clock generators, but it's not clear what they refer to:

• CLKSRC_PLL_USB_PRIMARY_REF_OPCG - how does this differ from CLKSRC_PLL_USB?
• OTP_CLK2FC - is this related to the OTP boot oscillator?
• ROSC_CLKSRC_PH - how does this differ from ROSC_CLKSRC?

Along with some of the above, the frequency counter also lists the following clock sources:

• PLL_SYS_CLKSRC_PRIMARY
• PLL_USB_CLKSRC_PRIMARY
• PLL_USB_CLKSRC_PRIMARY_DFT

A couple of other minor nits:

• Section 8.1.2 mentions that "the list of clock sources is different per clock generator". A matrix showing which sources are available on which clock generators would be extremely helpful.
• The behavior of the frequency counter isn't well explained. A quick explanation of the theory of operation would be nice. (For example: is the test interval based on a number of clk_ref cycles, or something else?)
• What are the units of the FRAC field in FC0_RESULT?
• Section 8.1.5 refers to the "CLOCKS_DEFAULT_IRQ processor interrupt", but the name is actually CLOCKS_IRQ.