diff --git a/ports/stm32/Makefile b/ports/stm32/Makefile
index 806added49e9..a9612f1a5792 100644
--- a/ports/stm32/Makefile
+++ b/ports/stm32/Makefile
@@ -640,15 +640,15 @@ $(BUILD)/%_$(BOARD).c $(HEADER_BUILD)/%.h $(HEADER_BUILD)/%_af_const.h $(HEADER_
 	    --output-source $(GEN_PINS_SRC) --output-header $(GEN_PINS_HDR) \
 		--output-af-const $(GEN_PINS_AF_CONST) --output-af-defs $(GEN_PINS_AF_DEFS)
 
-powerctrl.c: $(GEN_PLLFREQTABLE_HDR)
-$(GEN_PLLFREQTABLE_HDR): $(PLLVALUES) | $(HEADER_BUILD)
+$(BUILD)/powerctrl.o: $(GEN_PLLFREQTABLE_HDR)
+$(GEN_PLLFREQTABLE_HDR): $(PLLVALUES) | $(HEADER_BUILD)/qstr.i.last
 	$(ECHO) "GEN $@"
-	$(Q)$(PYTHON) $(PLLVALUES) -c -m $(CMSIS_MCU_LOWER) file:$(BOARD_DIR)/stm32$(MCU_SERIES)xx_hal_conf.h > $@
+	$(Q)$(PYTHON) $(PLLVALUES) -c -m $(CMSIS_MCU_LOWER) file:$(HEADER_BUILD)/qstr.i.last > $@
 
-$(TOP)/extmod/machine_i2s.c: $(GEN_PLLI2STABLE_HDR)
-$(GEN_PLLI2STABLE_HDR): $(PLLI2SVALUES) | $(HEADER_BUILD)
+$(BUILD)/extmod/machine_i2s.o: $(GEN_PLLI2STABLE_HDR)
+$(GEN_PLLI2STABLE_HDR): $(PLLI2SVALUES) | $(HEADER_BUILD)/qstr.i.last
 	$(ECHO) "GEN $@"
-	$(Q)$(PYTHON) $(PLLI2SVALUES) -c -m $(CMSIS_MCU_LOWER) hse:$(BOARD_DIR)/stm32$(MCU_SERIES)xx_hal_conf.h pllm:$(BOARD_DIR)/mpconfigboard.h > $@
+	$(Q)$(PYTHON) $(PLLI2SVALUES) -c -m $(CMSIS_MCU_LOWER) file:$(HEADER_BUILD)/qstr.i.last > $@
 
 $(BUILD)/modstm.o: $(GEN_STMCONST_HDR)
 $(HEADER_BUILD)/modstm_const.h: $(CMSIS_MCU_HDR) make-stmconst.py | $(HEADER_BUILD)
diff --git a/ports/stm32/boards/plli2svalues.py b/ports/stm32/boards/plli2svalues.py
index 8ff7f0ff8fcd..c2d581bb8e16 100644
--- a/ports/stm32/boards/plli2svalues.py
+++ b/ports/stm32/boards/plli2svalues.py
@@ -137,8 +137,11 @@ def search_header(filename, re_include, re_define, lookup, val):
             m = regex_define.match(line)
             if m:
                 # found lookup value
+                found = m.group(3)
+                if "*" in found or "/" in found:
+                    found = eval(found)
                 if m.group(1) == lookup:
-                    val[0] = int(m.group(3))
+                    val[0] = int(found)
     return val
 
 
@@ -166,35 +169,41 @@ def main():
             break
 
     if mcu_series in mcu_support_plli2s:
-        if len(argv) != 2:
+        if len(argv) not in (1, 2):
             print("usage: pllvalues.py [-c] [-m <mcu_series>] <hse in MHz> <pllm in MHz>")
             sys.exit(1)
 
         if argv[0].startswith("hse:"):
-            # extract HSE_VALUE from header file
+            hse = int(argv[0][len("hse:") :])
+
+        if argv[0].startswith("pllm:"):
+            pllm = int(argv[0][len("pllm:") :])
+
+        if argv[0].startswith("file:"):
+            # extract HSE_VALUE and from header file
             (hse,) = search_header(
-                argv[0][len("hse:") :],
+                argv[0][len("file:") :],
                 r'#include "(boards/[A-Za-z0-9_./]+)"',
-                r"#define +(HSE_VALUE) +\((\(uint32_t\))?([0-9]+)\)",
-                "HSE_VALUE",
+                r"static.* (micropy_hw_hse_value) = +\(*(\(uint32_t\))?([0-9 +-/\*]+)\)*;",
+                "micropy_hw_hse_value",
                 [None],
             )
             if hse is None:
-                raise ValueError("%s does not contain a definition of HSE_VALUE" % argv[0])
-            argv.pop(0)
+                raise ValueError(
+                    "%s does not contain a definition of micropy_hw_hse_value" % argv[0]
+                )
 
-        if argv[0].startswith("pllm:"):
             # extract MICROPY_HW_CLK_PLLM from header file
             (pllm,) = search_header(
-                argv[0][len("pllm:") :],
+                argv[0][len("file:") :],
                 r'#include "(boards/[A-Za-z0-9_./]+)"',
-                r"#define +(MICROPY_HW_CLK_PLLM) +\((\(uint32_t\))?([0-9]+)\)",
-                "MICROPY_HW_CLK_PLLM",
+                r"static.* (micropy_hw_clk_pllm) = +\(*(\(uint32_t\))?([0-9 +-/\*]+)\)*;",
+                "micropy_hw_clk_pllm",
                 [None],
             )
             if pllm is None:
                 raise ValueError(
-                    "%s does not contain a definition of MICROPY_HW_CLK_PLLM" % argv[0]
+                    "%s does not contain a definition of micropy_hw_clk_pllm" % argv[0]
                 )
             argv.pop(0)
 
diff --git a/ports/stm32/boards/pllvalues.py b/ports/stm32/boards/pllvalues.py
index 2db6b5f25704..293e157dc974 100644
--- a/ports/stm32/boards/pllvalues.py
+++ b/ports/stm32/boards/pllvalues.py
@@ -230,7 +230,9 @@ def print_table(hse, valid_plls):
 
 def search_header_for_hsx_values(filename, vals):
     regex_inc = re.compile(r'#include "(boards/[A-Za-z0-9_./]+)"')
-    regex_def = re.compile(r"#define +(HSE_VALUE|HSI_VALUE) +\((\(uint32_t\))?([0-9]+)\)")
+    regex_def = re.compile(
+        r"static.* +(micropy_hw_hs[ei]_value) = +\(*(\(uint32_t\))?([0-9 +-/\*]+)\)*;",
+    )
     with open(filename) as f:
         for line in f:
             line = line.strip()
@@ -242,8 +244,11 @@ def search_header_for_hsx_values(filename, vals):
             m = regex_def.match(line)
             if m:
                 # Found HSE_VALUE or HSI_VALUE
-                val = int(m.group(3)) // 1000000
-                if m.group(1) == "HSE_VALUE":
+                found = m.group(3)
+                if "*" in found or "/" in found:
+                    found = eval(found)
+                val = int(found) // 1000000
+                if m.group(1) == "micropy_hw_hse_value":
                     vals[0] = val
                 else:
                     vals[1] = val
@@ -282,7 +287,7 @@ def main():
         # extract HSE_VALUE, and optionally HSI_VALUE, from header file
         hse, hsi = search_header_for_hsx_values(argv[0][5:], [None, None])
         if hse is None:
-            raise ValueError("%s does not contain a definition of HSE_VALUE" % argv[0])
+            raise ValueError("%s does not contain a definition of micropy_hw_hse_value" % argv[0])
     else:
         # HSE given directly as an integer
         hse = int(argv[0])
diff --git a/ports/stm32/machine_i2s.c b/ports/stm32/machine_i2s.c
index a2a0a8291008..d7d4dc14b988 100644
--- a/ports/stm32/machine_i2s.c
+++ b/ports/stm32/machine_i2s.c
@@ -33,7 +33,9 @@
 #include "py/mphal.h"
 #include "pin.h"
 #include "dma.h"
+#ifndef NO_QSTR
 #include "genhdr/plli2stable.h"
+#endif
 
 // Notes on this port's specific implementation of I2S:
 // - the DMA callbacks (1/2 complete and complete) are used to implement the asynchronous background operations
diff --git a/ports/stm32/powerctrl.c b/ports/stm32/powerctrl.c
index 775514922721..391be85ae12e 100644
--- a/ports/stm32/powerctrl.c
+++ b/ports/stm32/powerctrl.c
@@ -28,8 +28,23 @@
 #include "py/mphal.h"
 #include "powerctrl.h"
 #include "rtc.h"
-#include "genhdr/pllfreqtable.h"
 #include "extmod/modbluetooth.h"
+#include "py/mpconfig.h"
+#ifndef NO_QSTR
+#include "genhdr/pllfreqtable.h"
+#endif
+
+// These will be defined / expanded in pre-processor output for use in the
+// boards/pllvalues.py script, then generally stripped from final firmware.
+#ifdef HSI_VALUE
+static uint32_t __attribute__((unused)) micropy_hw_hsi_value = HSI_VALUE;
+#endif
+#ifdef HSE_VALUE
+static uint32_t __attribute__((unused)) micropy_hw_hse_value = HSE_VALUE;
+#endif
+#ifdef MICROPY_HW_CLK_PLLM
+static uint32_t __attribute__((unused)) micropy_hw_clk_pllm = MICROPY_HW_CLK_PLLM;
+#endif
 
 #if defined(STM32H5) || defined(STM32H7)
 #define RCC_SR          RSR