Merge pull request #72 from riscv/16550

Add a 16550 UART driver to back the SBI console

5 files changed, 95 insertions, 0 deletions

diff --git a/machine/machine.mk.in b/machine/machine.mk.in
index dc8492f..3d19bf0 100644
--- a/machine/machine.mk.in
+++ b/machine/machine.mk.in
@@ -12,6 +12,7 @@ machine_hdrs = \
   mcall.h \
   mtrap.h \
   uart.h \
+  uart16550.h \
   finisher.h \
   unprivileged_memory.h \
   vm.h \
@@ -26,6 +27,7 @@ machine_c_srcs = \
   fp_emulation.c \
   fp_ldst.c \
   uart.c \
+  uart16550.c \
   finisher.c \
   misaligned_ldst.c \
 
diff --git a/machine/minit.c b/machine/minit.c
index 3623f38..ee83f98 100644
--- a/machine/minit.c
+++ b/machine/minit.c
@@ -4,6 +4,7 @@
 #include "fp_emulation.h"
 #include "fdt.h"
 #include "uart.h"
+#include "uart16550.h"
 #include "finisher.h"
 #include "disabled_hart_mask.h"
 #include "htif.h"
@@ -141,6 +142,7 @@ void init_first_hart(uintptr_t hartid, uintptr_t dtb)
 {
   // Confirm console as early as possible
   query_uart(dtb);
+  query_uart16550(dtb);
   query_htif(dtb);
 
   hart_init();
diff --git a/machine/mtrap.c b/machine/mtrap.c
index 0f77def..6c0e99c 100644
--- a/machine/mtrap.c
+++ b/machine/mtrap.c
@@ -5,6 +5,7 @@
 #include "bits.h"
 #include "vm.h"
 #include "uart.h"
+#include "uart16550.h"
 #include "finisher.h"
 #include "fdt.h"
 #include "unprivileged_memory.h"
@@ -22,6 +23,8 @@ static uintptr_t mcall_console_putchar(uint8_t ch)
 {
   if (uart) {
     uart_putchar(ch);
+  } else if (uart16550) {
+    uart16550_putchar(ch);
   } else if (htif) {
     htif_console_putchar(ch);
   }
@@ -73,6 +76,8 @@ static uintptr_t mcall_console_getchar()
 {
   if (uart) {
     return uart_getchar();
+  } else if (uart16550) {
+    return uart16550_getchar();
   } else if (htif) {
     return htif_console_getchar();
   } else {
diff --git a/machine/uart16550.c b/machine/uart16550.c
new file mode 100644
index 0000000..fe1ba99
--- /dev/null
+++ b/machine/uart16550.c
@@ -0,0 +1,74 @@
+#include <string.h>
+#include "uart16550.h"
+#include "fdt.h"
+
+volatile uint8_t* uart16550;
+
+#define UART_REG_QUEUE     0
+#define UART_REG_LINESTAT  5
+#define UART_REG_STATUS_RX 0x01
+#define UART_REG_STATUS_TX 0x20
+
+void uart16550_putchar(uint8_t ch)
+{
+  while ((uart16550[UART_REG_LINESTAT] & UART_REG_STATUS_TX) == 0);
+  uart16550[UART_REG_QUEUE] = ch;
+}
+
+int uart16550_getchar()
+{
+  if (uart16550[UART_REG_LINESTAT] & UART_REG_STATUS_RX)
+    return uart16550[UART_REG_QUEUE];
+  return -1;
+}
+
+struct uart16550_scan
+{
+  int compat;
+  uint64_t reg;
+};
+
+static void uart16550_open(const struct fdt_scan_node *node, void *extra)
+{
+  struct uart16550_scan *scan = (struct uart16550_scan *)extra;
+  memset(scan, 0, sizeof(*scan));
+}
+
+static void uart16550_prop(const struct fdt_scan_prop *prop, void *extra)
+{
+  struct uart16550_scan *scan = (struct uart16550_scan *)extra;
+  if (!strcmp(prop->name, "compatible") && !strcmp((const char*)prop->value, "ns16550a")) {
+    scan->compat = 1;
+  } else if (!strcmp(prop->name, "reg")) {
+    fdt_get_address(prop->node->parent, prop->value, &scan->reg);
+  }
+}
+
+static void uart16550_done(const struct fdt_scan_node *node, void *extra)
+{
+  struct uart16550_scan *scan = (struct uart16550_scan *)extra;
+  if (!scan->compat || !scan->reg || uart16550) return;
+
+  uart16550 = (void*)(uintptr_t)scan->reg;
+  // http://wiki.osdev.org/Serial_Ports
+  uart16550[1] = 0x00;    // Disable all interrupts
+  uart16550[3] = 0x80;    // Enable DLAB (set baud rate divisor)
+  uart16550[0] = 0x03;    // Set divisor to 3 (lo byte) 38400 baud
+  uart16550[1] = 0x00;    //                  (hi byte)
+  uart16550[3] = 0x03;    // 8 bits, no parity, one stop bit
+  uart16550[2] = 0xC7;    // Enable FIFO, clear them, with 14-byte threshold
+}
+
+void query_uart16550(uintptr_t fdt)
+{
+  struct fdt_cb cb;
+  struct uart16550_scan scan;
+
+  memset(&cb, 0, sizeof(cb));
+  cb.open = uart16550_open;
+  cb.prop = uart16550_prop;
+  cb.done = uart16550_done;
+  cb.extra = &scan;
+
+  fdt_scan(fdt, &cb);
+}
diff --git a/machine/uart16550.h b/machine/uart16550.h
new file mode 100644
index 0000000..d7a0805
--- /dev/null
+++ b/machine/uart16550.h
@@ -0,0 +1,12 @@
+#ifndef _RISCV_16550_H
+#define _RISCV_16550_H
+
+#include <stdint.h>
+
+extern volatile uint8_t* uart16550;
+
+void uart16550_putchar(uint8_t ch);
+int uart16550_getchar();
+void query_uart16550(uintptr_t dtb);
+
+#endif