Initial Release

clocks/hello_48MHz/CMakeLists.txt

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+add_executable(hello_48MHz
+        hello_48MHz.c
+        )
+
+# Pull in our pico_stdlib which pulls in commonly used features
+target_link_libraries(hello_48MHz pico_stdlib hardware_clocks)
+
+# create map/bin/hex file etc.
+pico_add_extra_outputs(hello_48MHz)
+
+# add url via pico_set_program_url
+example_auto_set_url(hello_48MHz)

clocks/hello_48MHz/hello_48MHz.c

@@ -0,0 +1,68 @@
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "pico/stdlib.h"
+#include "hardware/pll.h"
+#include "hardware/clocks.h"
+#include "hardware/structs/pll.h"
+#include "hardware/structs/clocks.h"
+
+void measure_freqs(void) {
+    uint f_pll_sys = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_PLL_SYS_CLKSRC_PRIMARY);
+    uint f_pll_usb = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_PLL_USB_CLKSRC_PRIMARY);
+    uint f_rosc = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_ROSC_CLKSRC);
+    uint f_clk_sys = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_SYS);
+    uint f_clk_peri = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_PERI);
+    uint f_clk_usb = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_USB);
+    uint f_clk_adc = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_ADC);
+    uint f_clk_rtc = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_RTC);
+
+    printf("pll_sys  = %dkHz\n", f_pll_sys);
+    printf("pll_usb  = %dkHz\n", f_pll_usb);
+    printf("rosc     = %dkHz\n", f_rosc);
+    printf("clk_sys  = %dkHz\n", f_clk_sys);
+    printf("clk_peri = %dkHz\n", f_clk_peri);
+    printf("clk_usb  = %dkHz\n", f_clk_usb);
+    printf("clk_adc  = %dkHz\n", f_clk_adc);
+    printf("clk_rtc  = %dkHz\n", f_clk_rtc);
+
+    // Can't measure clk_ref / xosc as it is the ref
+}
+
+int main() {
+    stdio_init_all();
+
+    printf("Hello, world!\n");
+
+    measure_freqs();
+
+    // Change clk_sys to be 48MHz. The simplest way is to take this from PLL_USB
+    // which has a source frequency of 48MHz
+    clock_configure(clk_sys,
+                    CLOCKS_CLK_SYS_CTRL_SRC_VALUE_CLKSRC_CLK_SYS_AUX,
+                    CLOCKS_CLK_SYS_CTRL_AUXSRC_VALUE_CLKSRC_PLL_USB,
+                    48 * MHZ,
+                    48 * MHZ);
+
+    // Turn off PLL sys for good measure
+    pll_deinit(pll_sys);
+
+    // CLK peri is clocked from clk_sys so need to change clk_peri's freq
+    clock_configure(clk_peri,
+                    0,
+                    CLOCKS_CLK_PERI_CTRL_AUXSRC_VALUE_CLK_SYS,
+                    48 * MHZ,
+                    48 * MHZ);
+
+    // Re init uart now that clk_peri has changed
+    stdio_init_all();
+
+    measure_freqs();
+    printf("Hello, 48MHz");
+
+    return 0;
+}