From 97797540cbd6e8d60c8c0bb194cd079172523c7a Mon Sep 17 00:00:00 2001
From: "Earle F. Philhower, III" <earlephilhower@yahoo.com>
Date: Sat, 6 Dec 2025 10:16:54 -0800
Subject: [PATCH] Fix rp2040.getFreeStack() on RP2350

Use the linker symbols for stack location instead of hardcoding values
which differ RP2040 to RP2350.

Fixed #3254
---
 cores/rp2040/RP2040Support.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/cores/rp2040/RP2040Support.h b/cores/rp2040/RP2040Support.h
index 811146565..12640b3af 100644
--- a/cores/rp2040/RP2040Support.h
+++ b/cores/rp2040/RP2040Support.h
@@ -276,6 +276,8 @@ extern RP2040 rp2040;
 extern void main1();
 extern "C" char __StackLimit;
 extern "C" char __bss_end__;
+extern "C" uint32_t __scratch_x_start__;
+extern "C" uint32_t __scratch_y_start__;
 extern "C" void setup1() __attribute__((weak));
 extern "C" void loop1() __attribute__((weak));
 extern "C" bool core1_separate_stack;
@@ -477,12 +479,12 @@ class RP2040 {
     */
     inline int getFreeStack() {
         const unsigned int sp = getStackPointer();
-        uint32_t ref = 0x20040000;
+        uint32_t ref = (uint32_t)&__scratch_x_start__;
         if (setup1 || loop1) {
             if (core1_separate_stack) {
-                ref = cpuid() ? (unsigned int)core1_separate_stack_address : 0x20040000;
+                ref = (uint32_t)(cpuid() ? core1_separate_stack_address : &__scratch_x_start__);
             } else {
-                ref = cpuid() ? 0x20040000 : 0x20041000;
+                ref = (uint32_t)(cpuid() ? &__scratch_x_start__ : &__scratch_y_start__);
             }
         }
         return sp - ref;