rp2/modmachine: Allow changing CPU clock frequency.

Using the standard machine.freq().

The safe ranges tested were 10 and 12-270MHz, at which USB REPL still
worked.  Requested settings can be checked with the script:
pico-sdk/src/rp2_common/hardware_clocks/scripts/vcocalc.py.  At frequencies
like 300MHz the script still signaled OK, but USB did not work any more.

1 files changed, 12 insertions, 3 deletions

diff --git a/ports/rp2/modmachine.c b/ports/rp2/modmachine.c
index dbaafabe8..139309281 100644
--- a/ports/rp2/modmachine.c
+++ b/ports/rp2/modmachine.c
@@ -36,6 +36,7 @@
 #include "hardware/clocks.h"
 #include "hardware/watchdog.h"
 #include "pico/bootrom.h"
+#include "pico/stdlib.h"
 #include "pico/unique_id.h"
 
 #define RP2_RESET_PWRON (1)
@@ -80,10 +81,18 @@ STATIC mp_obj_t machine_bootloader(void) {
 }
 MP_DEFINE_CONST_FUN_OBJ_0(machine_bootloader_obj, machine_bootloader);
 
-STATIC mp_obj_t machine_freq(void) {
-    return MP_OBJ_NEW_SMALL_INT(clock_get_hz(clk_sys));
+STATIC mp_obj_t machine_freq(size_t n_args, const mp_obj_t *args) {
+    if (n_args == 0) {
+        return MP_OBJ_NEW_SMALL_INT(clock_get_hz(clk_sys));
+    } else {
+        mp_int_t freq = mp_obj_get_int(args[0]);
+        if (!set_sys_clock_khz(freq / 1000, false)) {
+            mp_raise_ValueError(MP_ERROR_TEXT("cannot change frequency"));
+        }
+        return mp_const_none;
+    }
 }
-MP_DEFINE_CONST_FUN_OBJ_0(machine_freq_obj, machine_freq);
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_freq_obj, 0, 1, machine_freq);
 
 STATIC mp_obj_t machine_idle(void) {
     best_effort_wfe_or_timeout(make_timeout_time_ms(1));