rp2/modmachine.c: Allow to use the MCU clock for the peripherals.

By default, the peripheral clock for UART and SPI is set to 48 MHz
and will not be affected by the MCU clock change. This can be changed
by a second argument to machine.freq(freq, use_mcu_clk). If use_mcu_clck
is present and True, the mcu_clock is used for UART and SPI. Note
that UART and SPI baud rates may have to be re-configured after changing
the MCU clock.
The peripheral clock cannot be set to arbitrary values. So it follows
either the USB clock of 48MHz or the MCU clock.

Side change: Allow more than one argument for machine.freq().

Signed-off-by: robert-hh <robert@hammelrath.com>

docs/rp2/quickref.rst

@@ -36,7 +36,9 @@ The :mod:`machine` module::
     import machine
 
     machine.freq()          # get the current frequency of the CPU
-    machine.freq(240000000) # set the CPU frequency to 240 MHz
+    machine.freq(240000000) # set the CPU frequency to 240 MHz and keep
+                            # the UART frequency at 48MHz
+    machine.freq(125000000, True) # set the CPU and UART frequency to 125 MHz
 
 The :mod:`rp2` module::
 

extmod/modmachine.c

@@ -109,7 +109,7 @@ static mp_obj_t machine_freq(size_t n_args, const mp_obj_t *args) {
         return mp_const_none;
     }
 }
-MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_freq_obj, 0, 1, machine_freq);
+MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_freq_obj, 0, 4, machine_freq);
 
 static mp_obj_t machine_lightsleep(size_t n_args, const mp_obj_t *args) {
     mp_machine_lightsleep(n_args, args);

ports/rp2/modmachine.c

@@ -96,6 +96,13 @@ static void mp_machine_set_freq(size_t n_args, const mp_obj_t *args) {
     if (!set_sys_clock_khz(freq / 1000, false)) {
         mp_raise_ValueError(MP_ERROR_TEXT("cannot change frequency"));
     }
+    if (n_args > 1 && mp_obj_get_int(args[1]) != 0) {
+        clock_configure(clk_peri,
+            0,
+            CLOCKS_CLK_PERI_CTRL_AUXSRC_VALUE_CLKSRC_PLL_SYS,
+            freq,
+            freq);
+    }
     #if MICROPY_HW_ENABLE_UART_REPL
     setup_default_uart();
     mp_uart_init();