From 23a2994e051488561294050993f16162f24a85e7 Mon Sep 17 00:00:00 2001
From: Vegard Storheil Eriksen <zyp@jvnv.net>
Date: Sat, 10 Sep 2022 20:18:42 +0200
Subject: startup: Add RISC-V reset handler.

---
 SConscript                      |  2 +-
 platforms/riscv.yaml            |  5 ++++-
 startup/SConscript              | 12 ++++++++++++
 startup/riscv_reset_handler.cpp | 11 +++++++++++
 4 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 startup/SConscript
 create mode 100644 startup/riscv_reset_handler.cpp

diff --git a/SConscript b/SConscript
index 7d3ff74..1378e7d 100644
--- a/SConscript
+++ b/SConscript
@@ -22,7 +22,7 @@ env.Append(
 		env.SConscript('usb/SConscript'),
 		env.SConscript('display/SConscript'),
 		env.SConscript('wpan/SConscript'),
-		Glob('startup/*.cpp'),
+		env.SConscript('startup/SConscript'),
 		Glob('os/*.cpp'),
 	],
 )
diff --git a/platforms/riscv.yaml b/platforms/riscv.yaml
index 16db64b..f66a3ef 100644
--- a/platforms/riscv.yaml
+++ b/platforms/riscv.yaml
@@ -33,7 +33,10 @@
       8: UEI
       9: SEI
       11: MEI
-  
+
+  startup:
+    - riscv_reset_handler
+
   toolchains:
     - riscv64-unknown-elf
 
diff --git a/startup/SConscript b/startup/SConscript
new file mode 100644
index 0000000..971f9fa
--- /dev/null
+++ b/startup/SConscript
@@ -0,0 +1,12 @@
+Import('env')
+
+sources = [
+    File('entry.cpp'),
+]
+
+startup = env['PLATFORM_SPEC'].get('startup', [])
+
+for file in startup:
+    sources.append(File(f'{file}.cpp'))
+
+Return('sources')
diff --git a/startup/riscv_reset_handler.cpp b/startup/riscv_reset_handler.cpp
new file mode 100644
index 0000000..0eed06d
--- /dev/null
+++ b/startup/riscv_reset_handler.cpp
@@ -0,0 +1,11 @@
+void entry();
+extern int _ram_end;
+
+[[gnu::naked]]
+[[gnu::section(".vectors")]]
+void _reset_handler() {
+    // Initialize stack pointer.
+    asm volatile("lui sp, %%hi(%0); add sp, sp, %%lo(%0)" :: "i"(&_ram_end));
+    // Absolute jump to entry function.
+    asm volatile("jr %0" :: "m"(entry));
+}
-- 
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