Overclock to 153.6 MHz (instead of 147.6 MHz) for I²S 48 kHz sample rate (earlephilhower#2708)

Author: magy00

docs/i2s.rst

@@ -71,7 +71,7 @@ sample rate on-the-fly.
 bool setSysClk(int samplerate) 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Changes the PICO system clock to optimise for the desired samplerate. 
-The clock changes to 147.6 MHz for samplerates that are a multiple of 8 kHz, and 135.6 MHz for multiples of 11.025 kHz.
+The clock changes to 153.6 MHz for samplerates that are a multiple of 8 kHz, and 135.6 MHz for multiples of 11.025 kHz.
 Note that using ``setSysClk()`` may affect the timing of other sysclk-dependent functions.
 Should be called before any I2S functions and any other sysclk dependent initialisations.
 

libraries/I2S/src/I2S.cpp

@@ -123,12 +123,10 @@ bool I2S::setFrequency(int newFreq) {
 
 bool I2S::setSysClk(int samplerate) { // optimise sys_clk for desired samplerate
     if (samplerate % 11025 == 0) {
-        set_sys_clock_khz(I2SSYSCLK_44_1, false); // 147.6 unsuccessful - no I2S no USB
-        return true;
+        return set_sys_clock_khz(I2SSYSCLK_44_1, false);
     }
     if (samplerate % 8000 == 0) {
-        set_sys_clock_khz(I2SSYSCLK_8, false);
-        return true;
+        return set_sys_clock_khz(I2SSYSCLK_8, false);
     }
     return false;
 }

libraries/I2S/src/I2S.h

@@ -163,5 +163,5 @@ class I2S : public Stream, public AudioOutputBase {
     int _sm, _smMCLK;
 
     static const int I2SSYSCLK_44_1 = 135600; // 44.1, 88.2 kHz sample rates
-    static const int I2SSYSCLK_8 = 147600;  // 8k, 16, 32, 48, 96, 192 kHz
+    static const int I2SSYSCLK_8 = 153600;  // 8k, 16, 32, 48, 96, 192 kHz
 };