rp2040: add multicore support

targets/arm.ld

@@ -32,6 +32,14 @@ SECTIONS
         _stack_top = .;
     } >RAM
 
+    /* Stack for second core (core 1), if there is one. */
+    .stack1 (NOLOAD) :
+    {
+        . = ALIGN(4);
+        . += DEFINED(__num_stacks) && __num_stacks >= 2 ? _stack_size : 0;
+        _stack1_top = .;
+    } >RAM
+
     /* Start address (in flash) of .data, used by startup code. */
     _sidata = LOADADDR(.data);
 

targets/rp2040.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["cortex-m0plus"],
     "build-tags": ["rp2040", "rp"],
+    "scheduler": "cores",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "serial": "usb",
@@ -12,6 +13,9 @@
     "extra-files": [
         "src/device/rp/rp2040.s"
     ],
+    "ldflags": [
+        "--defsym=__num_stacks=2"
+    ],
     "linkerscript": "targets/rp2040.ld",
     "openocd-interface": "picoprobe",
     "openocd-transport": "swd",