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P1 Clock Frequency
In C code, the P1 clock frequency defaults to 80 MHz, assuming a 5 MHz crystal and xtal1 + pll16x clock mode. This is a common configuration. You may override it with the builtin clkset function, which works the same as the Spin clkset builtin.
clkset(%01101100, 4_000_000) 'Set to XTAL1 + PLL2x