rp2040: support usb_request_bootloader

Signed-off-by: Lasse Dalegaard <dalegaard@gmail.com>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/rp2040/bootrom.c

@@ -0,0 +1,25 @@
+// Hardware interface to bootrom on rp2040
+//
+// Copyright (C) 2021  Lasse Dalegaard <dalegaard@gmail.com>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include <stdint.h> // uint16_t, uint32_t, uintptr_t
+
+static void *
+rom_func_lookup(uint32_t code)
+{
+  // Table and lookup function are provided by the BOOTROM
+  void *(*fn)(uint16_t *, uint32_t) =
+      (void *)(uintptr_t)(*(uint16_t *)0x18);
+  uint16_t *table = (uint16_t *)(uintptr_t)(*(uint16_t *)0x14);
+  return fn(table, code);
+}
+
+void
+reset_to_usb_boot(uint32_t gpio_activity_pin_mask
+                  , uint32_t disable_interface_mask)
+{
+  void (*reset_to_usb_boot)(uint32_t, uint32_t) = rom_func_lookup(0x4255);
+  reset_to_usb_boot(gpio_activity_pin_mask, disable_interface_mask);
+}