some ugly instructions (I wouldn't call this code), that switch to PL0 and check that MMU really works here - it's temporary, don't merge! (merge commit b4 PL0_test.c was added, if you really want)

1 files changed, 17 insertions, 1 deletions

diff --git a/PL0_test.c b/PL0_test.c
index 1a3d49d..7609294 100644
--- a/PL0_test.c
+++ b/PL0_test.c
@@ -1,9 +1,25 @@
 #include "uart.h"
+#include "psr.h"
 
 void PL0_main(void)
 {
-  uart_puts("hello PL0!\n\r");
+  uart_puts("hello PL0! Switching to user mode!\n\r");
 
+  asm("cps #0b10000\n\r"
+      "isb" ::: "memory");
+
+  // if all went correct, Success! gets printed
+  uart_puts("Success!\n\r");
+
+  // if we're indeed i PL0, we should crash now, when trying to access
+  // memory we're not allowed to
+  char first_kernel_byte[2];
+
+  first_kernel_byte[0] = *(char*) ((uint32_t) 0x8000);
+  first_kernel_byte[1] = '\0';
+  
+  uart_puts(first_kernel_byte);
+    
   while (1)
     {
       char c;