check paging support in kernel_main()

1 files changed, 21 insertions, 1 deletions

diff --git a/kernel.c b/kernel.c
index 6d09ce7..b7fa1bf 100644
--- a/kernel.c
+++ b/kernel.c
@@ -137,7 +137,27 @@ void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags)
  
   uart_init();
   uart_puts("Hello, kernel World!\r\n");
- 
+
+  uint32_t ID_MMFR0;
+  // get contents of coprocessor register to check for paging support
+  asm("mrc p15, 0, %0, c0, c1, 4" : "=r" (ID_MMFR0));
+
+  char *paging;
+
+  uart_puts("hmmm\n\r");
+  
+  switch(ID_MMFR0 & 7) /* lowest 4 bits indicate VMSA support */ {
+  case 0 : paging = "no paging\n\r"; break;
+  case 1 : paging = "implementation defined paging\n\r"; break;
+  case 2 : paging = "VMSAv6, with cache and TLB type registers\n\r"; break;
+  case 3 : paging = "VMSAv7, with support for remapping and access flag\n\r"; break;
+  case 4 : paging = "VMSAv7 with PXN bit supported\n\r"; break;
+  case 5 : paging = "VMSAv7, PXN and long format descriptors. EPAE is supported.\n\r"; break;
+  default : paging = "?_? unknown paging ?_?\n\r";
+  }
+
+  uart_puts(paging);
+  
   while (1)
     uart_putc(uart_getc());
 }