make things work again on real hw (setting system mode moved to boot.S)

6 files changed, 13 insertions, 67 deletions

diff --git a/Makefile b/Makefile
index 0796ac8..d1d66fa 100644
--- a/Makefile
+++ b/Makefile
@@ -47,9 +47,9 @@ qemu-elf : kernel.elf
 qemu-bin : loader.elf kernel.img pipe_image
 	./pipe_image --stdout | qemu-system-arm -m 256 -M raspi2 -serial stdio -kernel $<
 
-run-on-rpi : kernel7.img pipe_image
+run-on-rpi : kernel.img pipe_image
 	./pipe_image --stdout | sudo socat FILE:/dev/ttyUSB0,b115200,raw -
-#	screen  /dev/ttyUSB0 115200,cs8,-parenb,-cstopb,-hupcl
+	screen  /dev/ttyUSB0 115200,cs8,-parenb,-cstopb,-hupcl
 
 pipe_image : pipe_image.c lib/rs232/rs232.c
 	gcc -Wall -std=gnu99 -O3 $^ -o $@
diff --git a/boot.S b/boot.S
index 5cce37c..5e510f8 100644
--- a/boot.S
+++ b/boot.S
@@ -20,7 +20,11 @@ _start:
         and r5, r5, #3
         cmp r5, #0
         bne halt
- 
+
+	// go to system mode
+	cps #0b11111
+	isb
+	
         // Setup the stack.
 	// It shall be directly below our kernel image
         ldr r5, =__start
diff --git a/demo_functionality.c b/demo_functionality.c
index 60b0bfa..3375550 100644
--- a/demo_functionality.c
+++ b/demo_functionality.c
@@ -26,11 +26,11 @@ void demo_paging_support(void)
   uart_puts(paging);
 }
 
-void demo_mode_to_system(void)
+void demo_current_mode(void)
 {
 
   // get content of current program status register to check the current
-  // processor mode
+  // processor mode (should be system, as we set it in boot.S)
   PSR_t CPSR = read_CPSR();
 
   char *mode_name;
@@ -51,9 +51,6 @@ void demo_mode_to_system(void)
 
   uart_puts("current mode: ");
   uart_puts(mode_name);
-
-  uart_puts("setting mode to system (PL1)...\r\n");
-  set_system_mode();
 }
 
 #define TRANSLATION_TABLE						\
diff --git a/demo_functionality.h b/demo_functionality.h
index 73a284b..12f5807 100644
--- a/demo_functionality.h
+++ b/demo_functionality.h
@@ -3,7 +3,7 @@
 
 void demo_paging_support(void);
 
-void demo_mode_to_system(void);
+void demo_current_mode(void);
 
 void demo_setup_libkernel(void);
 
diff --git a/kernel.c b/kernel.c
index eb3e811..fc629e1 100644
--- a/kernel.c
+++ b/kernel.c
@@ -14,15 +14,15 @@ void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags)
   // When we attach screen session after loading kernel with socat
   // we miss kernel's greeting... So we'll make the kernel wait for
   // one char we're going to send from within screen
-  //  uart_getc();
+  uart_getc();
   
   uart_puts("Hello, kernel World!\r\n");
 
   // prints some info
   demo_paging_support();
 
-  // prints some info and switches to system mode
-  demo_mode_to_system();
+  // prints some info
+  demo_current_mode();
 
   // prints some info and sets upp translation table, turns on MMU
   setup_flat_map();
diff --git a/psr.h b/psr.h
index dfbb878..9809fc4 100644
--- a/psr.h
+++ b/psr.h
@@ -64,59 +64,4 @@ inline static PSR_t read_CPSR(void)
   return CPSR;
 }
 
-//// Write function not working for some reason... Assembly from gcc
-//// looks ok. Needs checking on real hw.
-
-//inline static void write_CPSR(PSR_t CPSR)
-//{
-  // write to current program status register and synchronize context
-  //  asm("msr cpsr, %0\n\r"
-  //      "isb" :: "r" (CPSR.raw) : "memory");
-//}
-
-inline static void set_system_mode(void)
-{
-  // hack to fix an unexplained bug; volatile needed in case of
-  // compilation with optimizations
-  volatile PSR_t CPSR __attribute__((unused)) = read_CPSR();
-
-  //// there are 2 ways of changing mode, both with the same
-  //// problem (see the long comment below)
-
-  //// way 1
-  // CPSR.fields.M_4_0 = MODE_SYSTEM;
-  // write to current program status register and synchronize context
-  // asm("msr cpsr, %0\n\r"
-  //     "isb":: "r" (CPSR.raw) : "memory");  
-
-  //// way 2
-  asm("cps #0b11111\n\r"
-      "isb" ::: "memory");
-}
-
-// The thing with writing to cpsr is weird. I used to have a single
-// function that would set the system mode by:
-//   1. reading the cpsr
-//   2. modifying the value using bit shifts and logical or
-//   3. writing the value back
-// When introducing structs and bitfields I wanted to have separate
-// functions for reading and writing the cpsr and have code up the
-// call stack handle value modification. For some reason this didn't
-// work - all would just hang when writing the CPSR. It turned out
-// everything works if i call read_CPSR() from the same function, in
-// which i write to cpsr. And I don't even need to use the value
-// I read. I can just discard it (we're compiling without
-// optimizations, so read_CPSR() is still called) and use the value
-// passed as argument. I noticed an even weirder thing: the 2nd way
-// of changing mode (cps instruction) doesn't work normally, but,
-// just as msr, it does work when I call read_CPSR() before it. Even
-// weirder - I cannot replace read_CPSR() with the actual assembly it
-// does, because it stops working again! Asm generated by gcc looks
-// ok, so Idk, maybe its some qemu issue (haven't tested on real RPi
-// yet). I seem to have experienced uart printing inserted here and
-// there do the same magic read_CPSR() does (but, again, not always).
-// Unfortunately, nop repeated several hundreds times (or a recursive
-// nop function, that just calls itself a given number of times)
-// doesn't have this magical property :(
-
 #endif // PSR_H