Reported system clock rate incorrect when configuring pll settings in cmakelists #2014
Description
I need some specific system clock rates for my audio-related project with an external ADC. Found the vcocalc.py script after some quick searches. It shows the option to configure the system pll from cmake instead of in the c code, e.g.
target_compile_definitions(audio PRIVATE
PLL_SYS_REFDIV=1
PLL_SYS_VCO_FREQ_HZ=1476000000
PLL_SYS_POSTDIV1=5
PLL_SYS_POSTDIV2=2
)
This seems to work as intended, checking the system clock rate with a frequency counter gave me 147.6 MHz, as expected.
However, the value returned by clock_get_hz is still 150 MHz (pico 2).
If I also set SYS_CLK_HZ in cmake, clock_get_hz will return this value, but it will return whatever value I put into cmake.
Looking into the code I think this gets set here, which in turn simply uses the clock speed defined here.
If this is intended behaviour, perhaps the vcocalc.py script should include a line on also setting SYS_CLK_HZ in cmake?
Test code and output
uint32_t reported_before_setting = clock_get_hz(clk_sys);
uint32_t counted_before_setting = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_SYS);
uint32_t freq_hz = 123 * MHZ; // 123 MHz can give us close to the bitrate we need.
set_sys_clock_hz(freq_hz, true);
uint32_t reported_after_setting = clock_get_hz(clk_sys);
uint32_t counted_after_setting = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_SYS);
stdio_init_all();
puts("\n\n==== Pico is booted ====");
printf("Reported before: %ld, reported after %ld\n", reported_before_setting, reported_after_setting);
printf("Counted before: %ld, counted after %ld\n", counted_before_setting, counted_after_setting);
==== Pico is booted ====
Reported before: 137600000, reported after 123000000
Counted before: 147600, counted after 123000