From be9e35bafa5f13f4b26a1d965c3db4b59f4957f8 Mon Sep 17 00:00:00 2001
From: Zihao Yu <yuzihao@ict.ac.cn>
Date: Sun, 13 Oct 2019 21:15:37 +0800
Subject: [PATCH] device,serial: add registers to keep compatible to 16550

---
 src/device/serial.c | 44 +++++++++++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/src/device/serial.c b/src/device/serial.c
index 5bf249db..dc37ace5 100644
--- a/src/device/serial.c
+++ b/src/device/serial.c
@@ -2,16 +2,21 @@
 #include "device/map.h"
 
 /* http://en.wikibooks.org/wiki/Serial_Programming/8250_UART_Programming */
+// NOTE: this is compatible to 16550
 
 #define SERIAL_PORT 0x3F8
 #define SERIAL_MMIO 0xa10003F8
+
 #define CH_OFFSET 0
+#define LSR_OFFSET 5
+#define LSR_TX_READY 0x20
+#define LSR_RX_READY 0x01
 
 #define QUEUE_SIZE 1024
 static char queue[QUEUE_SIZE] = {};
 static int f = 0, r = 0;
 
-static uint8_t *serial_ch_base = NULL;
+static uint8_t *serial_base = NULL;
 
 static void serial_enqueue(char ch) {
   int next = (r + 1) % QUEUE_SIZE;
@@ -22,21 +27,26 @@ static void serial_enqueue(char ch) {
   }
 }
 
-static void serial_ch_io_handler(uint32_t offset, int len, bool is_write) {
-  assert(offset == 0);
-  assert(len == 1);
+static char serial_dequeue() {
+  char ch = 0xff;
+  if (f != r) {
+    ch = queue[f];
+    f = (f + 1) % QUEUE_SIZE;
+  }
+  return ch;
+}
 
-  if (is_write) {
-    char c = serial_ch_base[0];
+static void serial_io_handler(uint32_t offset, int len, bool is_write) {
+  assert(len == 1);
+  switch (offset) {
     /* We bind the serial port with the host stdout in NEMU. */
-    putc(c, stderr);
-  } else {
-    if (f != r) {
-      serial_ch_base[0] = queue[f];
-      f = (f + 1) % QUEUE_SIZE;
-    } else {
-      serial_ch_base[0] = 0xff;
-    }
+    case CH_OFFSET:
+      if (is_write) putc(serial_base[0], stderr);
+      else serial_base[0] = serial_dequeue();
+      break;
+    case LSR_OFFSET:
+      if (!is_write) serial_base[5] = LSR_TX_READY | LSR_RX_READY;
+      break;
   }
 }
 
@@ -49,9 +59,9 @@ static void preset_input() {
 }
 
 void init_serial() {
-  serial_ch_base = new_space(1);
-  add_pio_map("serial", SERIAL_PORT + CH_OFFSET, serial_ch_base, 1, serial_ch_io_handler);
-  add_mmio_map("serial", SERIAL_MMIO + CH_OFFSET, serial_ch_base, 1, serial_ch_io_handler);
+  serial_base = new_space(8);
+  add_pio_map("serial", SERIAL_PORT, serial_base, 8, serial_io_handler);
+  add_mmio_map("serial", SERIAL_MMIO, serial_base, 8, serial_io_handler);
 
   preset_input();
 }
-- 
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