stack pointer fixing

Author: outercloudstudio

README.md

@@ -130,7 +130,7 @@ nix-shell -p imagemagick --run "convert frame.ppm frame.png"
 
 .\xpack-riscv-none-elf-gcc-15.2.0-1\bin\riscv-none-elf-gcc.exe -c -O0 -march=rv32i -mabi=ilp32 ./programs/hello.c -o ./programs/hello.o
 
-.\xpack-riscv-none-elf-gcc-15.2.0-1\bin\riscv-none-elf-gcc.exe -march=rv32i -mabi=ilp32 -nostdlib "-Wl,--section-start=.text=0x0" -o ./programs/hello.elf ./programs/hello.o
+.\xpack-riscv-none-elf-gcc-15.2.0-1\bin\riscv-none-elf-gcc.exe -march=rv32i -mabi=ilp32 -nostdlib "-Wl,--section-start=.text=0x0,--entry=_start" -o ./programs/hello.elf ./programs/hello.o
 
 .\xpack-riscv-none-elf-gcc-15.2.0-1\bin\riscv-none-elf-objcopy.exe -O binary ./programs/hello.elf ./programs/hello.bin
 

programs/hello.c

@@ -1,3 +1,11 @@
+__attribute__((naked)) void _start(void) {
+    __asm__ volatile (
+        "li sp, 0x8000\n"   // top of 32KB RAM
+        "call main\n"
+        "loop: j loop\n"
+    );
+}
+
 int main() {
     volatile unsigned char* mem = (volatile unsigned char*)0x4000;
     int counter = 0;

src/test/scala/RISCV/MainSpec.scala

@@ -32,7 +32,7 @@ class MainSpec extends AnyFreeSpec with Matchers with ChiselSim {
             dut.clock.step(1)
 
             dut.io.execute.poke(true.B)
-            dut.clock.step(100)
+            dut.clock.step(64)
         }
     }