uart: add physical device driver

machine/machine.mk.in

@@ -11,6 +11,7 @@ machine_hdrs = \
   htif.h \
   mcall.h \
   mtrap.h \
+  uart.h \
   unprivileged_memory.h \
   vm.h \
 
@@ -23,6 +24,7 @@ machine_c_srcs = \
   muldiv_emulation.c \
   fp_emulation.c \
   fp_ldst.c \
+  uart.c \
   misaligned_ldst.c \
 
 machine_asm_srcs = \

machine/minit.c

@@ -3,6 +3,7 @@
 #include "vm.h"
 #include "fp_emulation.h"
 #include "fdt.h"
+#include "uart.h"
 #include <string.h>
 #include <limits.h>
 
@@ -125,6 +126,10 @@ void init_first_hart(uintptr_t hartid, uintptr_t dtb)
   hart_init();
   hls_init(0); // this might get called again from parse_config_string
 
+  // Confirm console as early as possible
+  query_uart(dtb);
+  printm("SBI console now online\n");
+
   query_mem(dtb);
   query_harts(dtb);
   query_clint(dtb);

machine/mtrap.c

@@ -4,6 +4,7 @@
 #include "atomic.h"
 #include "bits.h"
 #include "vm.h"
+#include "uart.h"
 #include "unprivileged_memory.h"
 #include <errno.h>
 #include <stdarg.h>
@@ -16,7 +17,11 @@ void __attribute__((noreturn)) bad_trap(uintptr_t* regs, uintptr_t dummy, uintpt
 
 static uintptr_t mcall_console_putchar(uint8_t ch)
 {
+  if (uart) {
+    uart_putchar(ch);
+  } else {
     htif_console_putchar(ch);
+  }
   return 0;
 }
 
@@ -52,8 +57,12 @@ static void send_ipi(uintptr_t recipient, int event)
 
 static uintptr_t mcall_console_getchar()
 {
+  if (uart) {
+    return uart_getchar();
+  } else {
     return htif_console_getchar();
   }
+}
 
 static uintptr_t mcall_clear_ipi()
 {

machine/uart.c

@@ -0,0 +1,38 @@
+#include "uart.h"
+#include "fdt.h"
+
+volatile uint32_t* uart;
+
+void uart_putchar(uint8_t ch)
+{
+#ifdef __riscv_atomic
+    int32_t r;
+    do {
+      __asm__ __volatile__ (
+        "amoor.w %0, %2, %1\n"
+        : "=r" (r), "+A" (uart[UART_REG_TXFIFO])
+        : "r" (ch));
+    } while (r < 0);
+#else
+    volatile uint32_t *tx = uart + UART_REG_TXFIFO;
+    while ((int32_t)(*tx) < 0);
+    *tx = ch;
+#endif
+}
+
+int uart_getchar()
+{
+  int32_t ch = uart[UART_REG_RXFIFO];
+  if (ch < 0) return -1;
+  return ch;
+}
+
+void query_uart(uintptr_t dtb)
+{
+  uart = 0; // (void*)fdt_get_reg(dtb, "sifive,uart0");
+  if (!uart) return;
+
+  // Enable Rx/Tx channels
+  uart[UART_REG_TXCTRL] = UART_TXEN;
+  uart[UART_REG_RXCTRL] = UART_RXEN;
+}

machine/uart.h

@@ -0,0 +1,21 @@
+#ifndef _RISCV_UART_H
+#define _RISCV_UART_H
+
+#include <stdint.h>
+
+extern volatile uint32_t* uart;
+
+#define UART_REG_TXFIFO		0
+#define UART_REG_RXFIFO		1
+#define UART_REG_TXCTRL		2
+#define UART_REG_RXCTRL		3
+#define UART_REG_DIV		4
+
+#define UART_TXEN		 0x1
+#define UART_RXEN		 0x1
+
+void uart_putchar(uint8_t ch);
+int uart_getchar();
+void query_uart(uintptr_t dtb);
+
+#endif