Update UART code to work with Raspi4

Author: mcribbs

src/common/stdio.c

@@ -3,11 +3,11 @@
 #include "stdlib.h"
 
 char getc() {
-    return uart_getc();
+    return uart_recv();
 }
 
 void putc(char c) {
-    uart_putc(c);
+    uart_send(c);
 }
 
 void puts(const char * str) {

src/common/utils.S

@@ -2,6 +2,15 @@
 get_core_id:
 	mrs x0, mpidr_el1
 	and x0, x0, #0xFF
+
+.globl put32
+put32:
+	str w1,[x0]
+	ret
+
+.globl get32
+get32:
+	ldr w0,[x0]
 	ret
 
 .globl delay

src/common/utils.h

@@ -5,6 +5,8 @@
 #ifndef __ASSEMBLER__
 
 extern unsigned int get_core_id ( void );
+extern void put32 ( unsigned long, unsigned int);
+extern unsigned int get32 ( unsigned long );
 extern void delay ( unsigned long );
 
 #endif

src/peripherals/uart.c

@@ -1,45 +1,55 @@
 #include "uart.h"
 #include "../common/utils.h"
 
-void uart_init()
+void uart_init (void)
 {
-    mmio_write(UART0_CR, 0x00000000);
-
-    mmio_write(GPPUD, 0x00000000);
-    delay(150);
-
-    mmio_write(GPPUDCLK0, (1 << 14) | (1 << 15));
-    delay(150);
-
-    mmio_write(GPPUDCLK0, 0x00000000);
-
-    mmio_write(UART0_ICR, 0x7FF);
-
-    mmio_write(UART0_IBRD, 1);
-    mmio_write(UART0_FBRD, 40);
-
-    mmio_write(UART0_LCRH, (1 << 4) | (1 << 5) | (1 << 6));
-
-    mmio_write(UART0_IMSC, (1 << 1) | (1 << 4) | (1 << 5) | (1 << 6) |
-            (1 << 7) | (1 << 8) | (1 << 9) | (1 << 10));
-
-    mmio_write(UART0_CR, (1 << 0) | (1 << 8) | (1 << 9));
+	unsigned int selector;
+	selector = get32(GPFSEL1);
+	selector &= ~(7<<12);                   // clean gpio14
+	selector |= 4<<12;                      // set alt0 for gpio14
+	selector &= ~(7<<15);                   // clean gpio15
+	selector |= 4<<15;                      // set alt0 for gpio 15
+	put32(GPFSEL1, selector);
+
+	put32(GPPUD, 0);
+	delay(150);
+	put32(GPPUDCLK0, (1<<14) | (1<<15));
+	delay(150);
+	put32(GPPUDCLK0, 0);
+
+	put32(UART0_CR, 0);                    // disable UART until configuration is done
+	/* baud divisor = UARTCLK / (16 * baud_rate) = 48 * 10^6 / (16 * 115200) = 26.0416666667
+     * integer part = 26
+	 * fractional part = (int) ((0.0416666667 * 64) + 0.5) = 3
+	 * generated baud rate divisor = 26 + (3 / 64) = 26.046875
+     * generated baud rate = (48 * 10^6) / (16 * 26.046875) = 115177
+	 * error = |(115177 - 115200) / 115200 * 100| = 0.02%
+	 */
+	put32(UART0_IBRD, 26);                 // baud rate divisor, integer part
+	put32(UART0_FBRD, 3);                  // baud rate divisor, fractional part
+	put32(UART0_LCRH, (1<<4) | (3<<5));    // enable FIFOs and 8 bits frames
+	put32(UART0_IMSC, 0);                  // mask interupts
+	put32(UART0_CR, 1 | (1<<8) | (1<<9));  // enable UART, receive and transmit
 }
 
-void uart_putc(unsigned char c)
+void uart_send (char c)
 {
-    while ( mmio_read(UART0_FR) & (1 << 5) ) { }
-    mmio_write(UART0_DR, c);
+	// wait for transmit FIFO to have an available slot
+	while(get32(UART0_FR) & (1<<5)) { }
+	put32(UART0_DR, c);
 }
 
-unsigned char uart_getc()
+char uart_recv ()
 {
-    while ( mmio_read(UART0_FR) & (1 << 4) ) { }
-    return mmio_read(UART0_DR);
+	// wait for receive FIFO to have data to read
+	while(get32(UART0_FR) & (1<<4)) { }
+	return(get32(UART0_DR) & 0xFF);
 }
 
-void uart_puts(const char* str)
+void uart_send_string(char* str)
 {
-    for (size_t i = 0; str[i] != '\0'; i ++)
-        uart_putc((unsigned char)str[i]);
-}
+	for (int i = 0; str[i] != '\0'; i ++) {
+		uart_send((char) str[i]);
+	}
+}
+

src/peripherals/uart.h

@@ -4,16 +4,21 @@
 #include <stdint.h>
 
 enum {
-    // The GPIO registers base address.
-    GPIO_BASE = 0x3F200000, // for raspi2 & 3, 0x20200000 for raspi1
-
-    GPPUD = (GPIO_BASE + 0x94),
-    GPPUDCLK0 = (GPIO_BASE + 0x98),
-
-    // The base address for UART.
-    UART0_BASE = 0x3F201000, // for raspi2 & 3, 0x20201000 for raspi1
-
-    UART0_DR     = (UART0_BASE + 0x00),
+	// The GPIO registers base address.
+	//GPIO_BASE		= 0x20200000 // raspi1
+	//GPIO_BASE		= 0x3f200000 // raspi2 & 3
+	GPIO_BASE		= 0xFE200000, // raspi4
+
+	// GPIO
+	GPFSEL1		= (GPIO_BASE + 0x04),
+	GPSET0		= (GPIO_BASE + 0x1C),
+	GPCLR0		= (GPIO_BASE + 0x28),
+	GPPUD		= (GPIO_BASE + 0x94),
+	GPPUDCLK0	= (GPIO_BASE + 0x98),
+
+	// The base address for UART.
+	UART0_BASE   = (GPIO_BASE + 0x1000),
+	UART0_DR     = (UART0_BASE + 0x00),
     UART0_RSRECR = (UART0_BASE + 0x04),
     UART0_FR     = (UART0_BASE + 0x18),
     UART0_ILPR   = (UART0_BASE + 0x20),
@@ -33,19 +38,11 @@ enum {
     UART0_TDR    = (UART0_BASE + 0x8C),
 };
 
-static inline void mmio_write(uint64_t reg, uint64_t data) {
-    *(volatile uint64_t*)reg = data;
-}
-
-static inline uint64_t mmio_read(uint64_t reg) {
-    return *(volatile uint64_t*)reg;
-}
-
 void uart_init();
 
 void uart_putc(unsigned char c);
 unsigned char uart_getc();
 
 void uart_puts(const char* str);
 
-#endif  /*_UAART_H */
+#endif  /*_UART_H */