dsp: add bootloader

It works!!

dsp/bootloader.c

@@ -0,0 +1,40 @@
+#include "sys.h"
+
+int main() {
+  uint16_t addr;
+  uint8_t len;
+  uint16_t val;
+
+  led0->output = 1;
+
+  while(1) {
+    uint8_t c = uart_read(uart0);
+    if (c == 'c') {
+      c = uart_read(uart0);
+      addr = c << 8;
+      c = uart_read(uart0);
+      addr |= c;
+
+      len = uart_read(uart0);
+      for (int i = 0; i < len; i += 2) {
+        c = uart_read(uart0);
+        val = c << 8;
+        c = uart_read(uart0);
+        val |= c;
+
+        *((uint16_t*)(addr + i)) = val;
+      }
+
+      uart_write(uart0, 'a');
+      uart_write(uart0, len);
+      led0->output = 0xf0;
+    } else if (c == 'j') {
+      c = uart_read(uart0);
+      addr = c << 8;
+      c = uart_read(uart0);
+      addr |= c;
+
+      ((void (*)())addr)();
+    }
+  }
+}