First commit for making lesson1 compatible with rpi4

Author: Vikash jha

src/lesson01/include/peripherals/base.h

@@ -1,6 +1,7 @@
 #ifndef	_P_BASE_H
 #define	_P_BASE_H
 
-#define PBASE 0x3F000000
+/* New raspberry pi-4 base address */
+#define PBASE 0xFE000000
 
 #endif  /*_P_BASE_H */

src/lesson01/src/config.txt

@@ -1,2 +1,2 @@
-kernel_old=1
-disable_commandline_tags=1
+# raspberry pi-4 lesson1
+arm_64bit=1

src/lesson01/src/mini_uart.c

@@ -49,7 +49,7 @@ void uart_init ( void )
 	put32(AUX_MU_IER_REG,0);                //Disable receive and transmit interrupts
 	put32(AUX_MU_LCR_REG,3);                //Enable 8 bit mode
 	put32(AUX_MU_MCR_REG,0);                //Set RTS line to be always high
-	put32(AUX_MU_BAUD_REG,270);             //Set baud rate to 115200
+	put32(AUX_MU_BAUD_REG,541);             //Set baud on raspberry pi-4 rate to 115200 (GPU clock rate is now 500Mhz)
 
 	put32(AUX_MU_CNTL_REG,3);               //Finally, enable transmitter and receiver
 }