exclusively use PLL_USB for clocking

myboard.c

@@ -26,16 +26,90 @@
 #include "tusb.h"
 #include <rp2040.h>
 
+#include "hardware/pll.h"
+
 /*
 This is a more streamlined alternative to the current pico-sdk based TinyUSB board support package.
 Sticking to C and avoiding all that C++ yields a much smaller executable.
 */
 
-void _usb_clock_setup(void); /* clock initialization routine borrowed from pico-bootrom */
+/* overhaul of clock_configure() from pico-sdk to use much less memory */
+bool simple_clock_configure(enum clock_index clk_index, uint32_t src, uint32_t auxsrc, bool glitchless)
+{
+  const uint32_t div = 0x100; /* always 1:1 ratio */
+
+  clock_hw_t *clock = &clocks_hw->clk[clk_index];
+
+  // If increasing divisor, set divisor before source. Otherwise set source
+  // before divisor. This avoids a momentary overspeed when e.g. switching
+  // to a faster source and increasing divisor to compensate.
+  if (div > clock->div)
+    clock->div = div;
+
+  // If switching a glitchless slice (ref or sys) to an aux source, switch
+  // away from aux *first* to avoid passing glitches when changing aux mux.
+  // Assume (!!!) glitchless source 0 is no faster than the aux source.
+  if (glitchless)
+  {
+    hw_clear_bits(&clock->ctrl, CLOCKS_CLK_REF_CTRL_SRC_BITS);
+    while (!(clock->selected & 1u));
+  }
+  // If no glitchless mux, cleanly stop the clock to avoid glitches
+  // propagating when changing aux mux. Note it would be a really bad idea
+  // to do this on one of the glitchless clocks (clk_sys, clk_ref).
+  else
+  {
+    hw_clear_bits(&clock->ctrl, CLOCKS_CLK_GPOUT0_CTRL_ENABLE_BITS);
+  }
+
+  // Set aux mux first, and then glitchless mux if this clock has one
+  hw_write_masked(&clock->ctrl,
+    (auxsrc << CLOCKS_CLK_SYS_CTRL_AUXSRC_LSB),
+    CLOCKS_CLK_SYS_CTRL_AUXSRC_BITS
+  );
+
+  if (glitchless)
+  {
+    hw_write_masked(&clock->ctrl,
+      src << CLOCKS_CLK_REF_CTRL_SRC_LSB,
+      CLOCKS_CLK_REF_CTRL_SRC_BITS
+    );
+    while (!(clock->selected & (1u << src)));
+  }
+
+  hw_set_bits(&clock->ctrl, CLOCKS_CLK_GPOUT0_CTRL_ENABLE_BITS);
+
+  // Now that the source is configured, we can trust that the user-supplied
+  // divisor is a safe value.
+  clock->div = div;
+
+  return true;
+}
+
+static void usb_clock_init(void)
+{
+  hw_set_bits(&resets_hw->reset, RESETS_RESET_PLL_USB_BITS);
+  hw_clear_bits(&resets_hw->reset, RESETS_RESET_PLL_USB_BITS);
+  while (~resets_hw->reset_done & RESETS_RESET_PLL_USB_BITS);
+
+  pll_init(pll_usb_hw, 1, 480 * 1000000, 5, 2);
+
+  // CLK SYS = PLL USB (48MHz) / 1 = 48MHz
+  simple_clock_configure(clk_sys,
+                  CLOCKS_CLK_SYS_CTRL_SRC_VALUE_CLKSRC_CLK_SYS_AUX,
+                  CLOCKS_CLK_SYS_CTRL_AUXSRC_VALUE_CLKSRC_PLL_USB,
+                  true);
+
+  // CLK USB = PLL USB (48MHz) / 1 = 48MHz
+  simple_clock_configure(clk_usb,
+                  0, // No GLMUX
+                  CLOCKS_CLK_USB_CTRL_AUXSRC_VALUE_CLKSRC_PLL_USB,
+                  false);
+}
 
 void board_init(void)
 {
-  _usb_clock_setup();
+  usb_clock_init();
 }
 
 void irq_set_exclusive_handler(unsigned int num, void *handler) {}

pico-debug.hzp

@@ -15,12 +15,12 @@
       <file file_name="./main.c" />
       <file file_name="./usb_descriptors.c" />
       <file file_name="myboard.c" />
-      <file file_name="clock_setup.c" />
       <file file_name="spawn.c" />
     </folder>
     <folder Name="hal">
       <file file_name="$(TOP)/hw/bsp/board.c" />
       <file file_name="$(TOP)/src/portable/raspberrypi/rp2040/rp2040_usb.c" />
+      <file file_name="$(TOP)/hw/mcu/raspberrypi/pico-sdk/src/rp2_common/hardware_pll/pll.c" />
     </folder>
     <folder Name="CMSIS-DAP">
       <file file_name="./CMSIS_5/CMSIS/DAP/Firmware/Source/DAP.c" />

usb_descriptors.c

@@ -23,7 +23,7 @@ tusb_desc_device_t const desc_device =
     /* using Dapper Miser CMSIS-DAP VID:PID */
     .idVendor           = 0x1209,
     .idProduct          = 0x2488,
-    .bcdDevice          = 0x1001,
+    .bcdDevice          = 0x1002,
 
     .iManufacturer      = 0,
     .iProduct           = STRID_PRODUCT,