Merge pull request #45 from sifive/double_tap_dontboot

Add the 'bootloader' which ships on HiFive1 Boards.

2 files changed, 154 insertions, 0 deletions

diff --git a/software/double_tap_dontboot/Makefile b/software/double_tap_dontboot/Makefile
new file mode 100644
index 0000000..ae89c51
--- /dev/null
+++ b/software/double_tap_dontboot/Makefile
@@ -0,0 +1,6 @@
+TARGET = double_tap_dontboot
+C_SRCS += double_tap_dontboot.c
+CFLAGS += -O2 -fno-builtin-printf -DNO_INIT
+
+BSP_BASE = ../../bsp
+include $(BSP_BASE)/env/common.mk
diff --git a/software/double_tap_dontboot/double_tap_dontboot.c b/software/double_tap_dontboot/double_tap_dontboot.c
new file mode 100644
index 0000000..0cae5b5
--- /dev/null
+++ b/software/double_tap_dontboot/double_tap_dontboot.c
@@ -0,0 +1,148 @@
+// See LICENSE for license details.
+
+// This is the 'bootloader' which ships on HiFive1 boards,
+// at SPI Flash location 0x20000000.
+// HiFive1 boards have code burned into their OTP which ends with
+// a jump to 0x20000000. The Freedom E SDK and the Arduino IDE
+// linker scripts cause user programs to be compiled and
+// flashed at 0x20400000. Therefore, this code ultimately jumps
+// to 0x20400000, while attempting to leave the machine state as close
+// to its reset state as possible.
+//
+// When compiled in the freedom-e-sdk environment, this code will
+// be compiled as a user program at 0x20400000, so will continuously jump to itself.
+// It is provided in the freedom-e-sdk mostly for reference purposes, so
+// users know what is running on their board. Replacing the bootloader
+// at 0x20000000 is not currently supported by the SDK.
+//
+// These are the instructions for the user of this program, from the
+// HiFive1 Getting Started Guide:
+// 
+// This program is designed to allow quick boot, but
+// also a "safe" reboot option if a "bad" program
+// is flashed into the HiFive1's SPI Flash. A "bad" program
+// is one which makes it impossible for the programmer
+// to communicate with the HiFive1. For example, a program which
+// disables FE310's active clock, or which puts the FE310 to sleep
+// with no way of waking it up. Bad programs can always be restarted using
+// the RESET button, and using the "safe" bootloader can be halted
+// before they perform any unsafe behavior.
+//
+// To activate "normal" boot mode, press the RESET button on
+// the HiFive1. After approximately 1s, the green LED will flash
+// for 1/2 second, then the user program will execute.
+//
+// To activate "safe" boot mode, press the RESET button. When
+// the green LED flashes, immediately press the RESET button again.
+// After 1 second, the red LED will blink. The user program will not
+// execute, and the programmer can connect. To exit "safe" boot mode,
+// press the RESET button a final time.
+
+#include <stdint.h>
+#include "platform.h"
+#include "encoding.h"
+
+#define BACKUP15_MAGIC 0xD027B007
+
+#define FINAL_ADDRESS 0x20400000
+
+#define RED_LED 22
+#define GREEN_LED 19
+
+int main(void)
+{
+  uint64_t now;
+  uint64_t then;
+  
+  // Restore the default mtvec (which may have been set by initialization
+  // code, depending on the environment in which this C code is compiled).
+  // By default, this would cause an infinite loop upon exception, which is
+  // also "safe" behavior and the debugger can connect.
+  
+  write_csr(mtvec, 0x0);
+  
+  // How did we get here? We only want to execute this code
+  // on resets (vs waking up from sleep).
+  if ((AON_REG(AON_PMUCAUSE) & AON_PMUCAUSE_WAKEUPCAUSE) ==
+      AON_WAKEUPCAUSE_RESET) {
+
+    if (AON_REG(AON_BACKUP15) == BACKUP15_MAGIC) {
+      // Reset was "double-tapped".
+
+      // Re-arm the reset double-tap
+      AON_REG(AON_BACKUP15) = 0;
+
+      // PWM Red LED
+
+      GPIO_REG(GPIO_IOF_EN)     |=   (1 << RED_LED);
+      GPIO_REG(GPIO_OUTPUT_XOR) &=  ~(1 << RED_LED);
+      GPIO_REG(GPIO_IOF_SEL)    |=   (1 << RED_LED);
+
+      GPIO_REG(GPIO_OUTPUT_VAL) &=  ~(1 << GREEN_LED);
+      GPIO_REG(GPIO_OUTPUT_XOR) &=  ~(1 << GREEN_LED);
+      GPIO_REG(GPIO_OUTPUT_EN)  &=  ~(1 << GREEN_LED);
+
+      PWM1_REG(PWM_CFG)   = 0;
+      PWM1_REG(PWM_COUNT) = 0;
+      PWM1_REG(PWM_CMP0)  = 0xFF;
+      PWM1_REG(PWM_CMP3)  = 0xFF;
+      PWM1_REG(PWM_CFG)   = PWM_CFG_ENALWAYS;
+
+      int pwm_val = 255;
+	
+      // Wait for debugger or another RESET press.
+      while(1){
+
+	// Make the PWM a fade. This is preferable to just a PWM blink
+	// because it makes it clear that the processor is actually
+	// running this code, not just the PWM hardware.
+
+	now = *((volatile uint64_t*) (CLINT_BASE_ADDR + CLINT_MTIME));
+	then = now + 32768/500;
+	while (*((volatile uint64_t*) (CLINT_BASE_ADDR + CLINT_MTIME)) < then) {
+	  asm volatile ("");
+	}
+	pwm_val = (pwm_val == 0) ? 255 : (pwm_val -1);
+	PWM1_REG(PWM_CMP3) = pwm_val << 4;
+      }
+           
+    } // If Magic
+      
+      // Turn on Green LED to indicate time-to-double-tap
+      // LEDs are Active-Low
+    GPIO_REG(GPIO_OUTPUT_VAL)     |=  (1 << GREEN_LED);
+    GPIO_REG(GPIO_OUTPUT_XOR)     |=  (1 << GREEN_LED);
+    GPIO_REG(GPIO_OUTPUT_EN)      |=  (1 << GREEN_LED);
+
+    // Re-arm the reset double-tap
+    uint32_t save = AON_REG(AON_BACKUP15);
+      
+    AON_REG(AON_BACKUP15) = BACKUP15_MAGIC;
+
+    // Wait 500 ms. If reset is tapped at this point,
+    // we will execute the "magic" loop above.
+    now = *((volatile uint64_t*) (CLINT_BASE_ADDR + CLINT_MTIME));
+    then = now + 32768/2;
+    while (*((volatile uint64_t*) (CLINT_BASE_ADDR + CLINT_MTIME)) < then) {
+      asm volatile ("");
+    }
+      
+    // Re-arm the reset double-tap
+    AON_REG(AON_BACKUP15) = save;
+   
+  }
+  
+  // Restore the GPIO Registers to their default
+  GPIO_REG(GPIO_OUTPUT_VAL)     = 0;
+  GPIO_REG(GPIO_OUTPUT_XOR)     = 0;
+  GPIO_REG(GPIO_OUTPUT_EN)      = 0;
+
+  // Jump to "user code" in SPI Flash.
+  void (*pgm_start)(void) = (void*) FINAL_ADDRESS;
+  pgm_start();
+
+  // This value is meaningless, but
+  // since this code should never be reached,
+  // make it non-zero.
+  return (1234567);
+}