FSBL improvmenets

 On branch master
 Your branch is up-to-date with 'origin/master'.

 Changes to be committed:
	modified:   src/fsbl/README.md
	modified:   src/fsbl/fsbl.c

src/fsbl/README.md

@@ -11,6 +11,9 @@ It is designed to work with the Xilinx UARTLite IP core.
 - That there is a Xilinx UARTLite IP core accessible at
   `0x4060000`.
 
+- That there is a Xilinx AXI GPIO IP core accessible at
+  `0x40000000`.
+
 - That the FSBL runs out of a *read only* memory.
 
 - That the core is set up such that the post-reset PC value points
@@ -43,3 +46,7 @@ It is designed to work with the Xilinx UARTLite IP core.
 
 6. The FSBL jumps to the specified start address, and relinquishes
    control to the downloaded program.
+
+At each step, an additional GPIO LED is turned on as a sort of "progress"
+indicator for debugging.
+

src/fsbl/fsbl.c

@@ -5,6 +5,12 @@
     #define UART_BASE 0x40600000
 #endif
 
+#ifndef GPIO_BASE
+    #define GPIO_BASE 0x40000000
+#endif
+
+#define GPIO_LEDS 2
+
 #define UART_RX 0
 #define UART_TX 1
 #define UART_ST 2
@@ -13,6 +19,8 @@
 // Pointer to the UART register space.
 static volatile uint32_t * uart = (volatile uint32_t*)(UART_BASE);
 
+static volatile uint32_t * gpio = (volatile uint32_t*)(GPIO_BASE);
+
 const uint32_t UART_CTRL_RST_TX_FIFO = 0x00000001;
 const uint32_t UART_CTRL_RST_RX_FIFO = 0x00000002;
 const uint32_t UART_CTRL_INT_ENA     = 0x00000010;
@@ -51,12 +59,12 @@ void fsbl_print_welcome() {
     // Welcome message
     char * welcome = "scarv-cpu fsbl\n";
 
-    for(char * p = welcome; *p != 0; p++ ) {
+    for(int i = 0; welcome[i]; i ++) {
 
         while(uart[UART_ST] & UART_STATUS_TX_FULL) {
             // Do nothing.
         }   
-        uart[UART_TX] = *p;
+        uart[UART_TX] = welcome[i];
 
     }
 }
@@ -66,23 +74,33 @@ void fsbl_print_welcome() {
 */
 void fsbl() {
 
+    gpio[GPIO_LEDS] = 0x1;
+
     fsbl_uart_setup();
+
+    gpio[GPIO_LEDS] = 0x3;
 
     fsbl_print_welcome();
 
+    gpio[GPIO_LEDS] = 0x7;
+
     // First 4 bytes are the size of the program (in bytes).
     uint32_t    program_size =
         ((uint32_t)uart_rd_char() << 24) |
         ((uint32_t)uart_rd_char() << 16) |
         ((uint32_t)uart_rd_char() <<  8) |
         ((uint32_t)uart_rd_char() <<  0) ;
 
+    gpio[GPIO_LEDS] = 0xF;
+
     // Next 4 bytes are a 32-bit destination address.
     uint32_t    program_dest =
         ((uint32_t)uart_rd_char() << 24) |
         ((uint32_t)uart_rd_char() << 16) |
         ((uint32_t)uart_rd_char() <<  8) |
         ((uint32_t)uart_rd_char() <<  0) ;
+
+    gpio[GPIO_LEDS] = 0x1F;
 
     uint8_t * dest_ptr = (uint8_t*)program_dest;
 
@@ -92,6 +110,8 @@ void fsbl() {
         dest_ptr[i] = uart_rd_char();
 
     }
+
+    gpio[GPIO_LEDS] = 0x3F;
 
     // Jump to the downloaded program.
     __fsbl_goto_main((uint32_t*)program_dest);