From: acevest <zhaoyanbai@126.com>
Date: Sat, 11 May 2024 04:39:00 +0000 (+0800)
Subject: 处理ticks可能减为负的情况
X-Git-Url: http://zhaoyanbai.com/repos/%22http:/www.isc.org/icons/zlib_tech.html?a=commitdiff_plain;h=c048943b34957ae7f4927f0b5e5316da039ea2ac;p=kernel.git

处理ticks可能减为负的情况
---

diff --git a/boot/boot.c b/boot/boot.c
index f7ad9f0..7498796 100644
--- a/boot/boot.c
+++ b/boot/boot.c
@@ -53,7 +53,7 @@ void setup_gdt();
 void setup_idt();
 void setup_gates();
 void set_tss();
-void setup_i8253(uint16_t);
+void setup_i8254(uint16_t);
 void setup_boot_irqs();
 
 void check_kernel(unsigned long addr, unsigned long magic) {
@@ -78,7 +78,7 @@ void check_kernel(unsigned long addr, unsigned long magic) {
 
     setup_boot_irqs();
 
-    setup_i8253(100);
+    setup_i8254(100);
 
     boot_delay(DEFAULT_BOOT_DELAY_TICKS);
 
diff --git a/kernel/clock.c b/kernel/clock.c
index f992557..5110a43 100644
--- a/kernel/clock.c
+++ b/kernel/clock.c
@@ -39,27 +39,36 @@ void clk_handler(unsigned int irq, pt_regs_t *regs, void *dev_id) {
     current->jiffies = jiffies;
 
     // 中断目前虽然不能嵌套，但依然可以打断前一个中断的下半部分处理
-    // 若前一个时钟中断将这个值减到0
-    // 同时其下半部分处理时间过长，直到这个时钟中断还没处理完
-    // 那么这个时钟中断是完全可以打断它，且在这里把这个ticks从0减到负数
-    // 而这个是uint32_t型，因此会溢出成0xFFFFFFFF
-    // if (current->ticks > 0) {
-    //     current->ticks--;
-    // }
-    if (0 == --current->ticks) {
-        current->need_resched = 1;
+    // 若前一个时钟中断将这个值减到0，会将该进程设置为need_resched，同时分配新的时间片值，以在下半部处理完后再重新调度就绪进程运行
+    // 而如果其下半部分需要处理的事情很多，处理时间过长，两个时钟中断之间的时间还不足以处理完
+    // 那么下一个时钟中断是完全可以打断还没处理完的下半部逻辑
+    // 打断后该时钟中断不应该继续减少该进程的时间片，因为这会造成该进程在后续的调底中少了实际的运行时间
+
+    if (1 == current->need_resched) {
+        // 这种情况必然已经发生了该时钟中断打断了下半部处理程序
+        return;
     }
 
+    current->ticks--;
+
+#if 1
     int value = (int)(current->ticks);
 
     if (min_ticks_value > value) {
         min_ticks_value = value;
         min_ticks_name = current->name;
     }
+#endif
 
-    printl(MPL_TEST, "%20s %10d %20s %10d", min_ticks_name, min_ticks_value, current->name, value);
+    if (0 == current->ticks) {
+        current->need_resched = 1;
+        current->ticks = current->priority;
+        current->turn++;
+    }
+
+    assert(current->ticks <= TASK_MAX_PRIORITY);  // 防止ticks被减到0后再减溢出
 
-    // assert(current->ticks <= TASK_MAX_PRIORITY);  // 防止ticks被减到0后再减溢出
+    printl(MPL_TEST, "%20s %10d %20s %10d", min_ticks_name, min_ticks_value, current->name, value);
 
     add_irq_bh_handler(clk_bh_handler, NULL);
 }
@@ -88,23 +97,56 @@ void clk_bh_handler(void *arg) {
     debug_print_all_tasks();
 }
 
-void setup_i8253(uint16_t hz) {
-    // 最低频率为18.2Hz(1193180/65536，最大计数值是65536是因为往计数器里写0就从65536开始计数)
+uint16_t read_i8254_counter(uint8_t counter_no) {
+    const uint8_t i8254_cmd_port = 0x43;
+    const uint8_t i8254_data_port = 0x40 + counter_no;
+
+    assert(counter_no < 3);
+
+    uint8_t cmd = 0x00;
+    cmd |= 0x03 << 6;                 // read back command
+    cmd |= 0x01 << 4;                 // don't latch status
+    cmd |= 0x01 << (counter_no + 1);  // read back timer channel n
+
+    uint16_t value = 0;
+
+    outb_p(cmd, i8254_cmd_port);
+
+    value |= inb(i8254_data_port) << 0;
+    value |= inb(i8254_data_port) << 8;
+
+    return value;
+}
+
+void setup_i8254(uint16_t hz) {
+    // PC/AT 8254的连接方法
+    // 第0个计数器连连到了8259A的IRQ0
+    // 第1个计数器连连到了DRAM刷新电路，通常情况下，该通道的频率设置为15.2kHz
+    // 第2个计数器连连到了音频驱动单元，可以通过频率控制发声
+
+    // 8254的最低频率为18.2Hz(1193180/65536，最大计数值是65536是因为往计数器里写0就从65536开始计数)
     assert(hz >= 19);
 
     const uint8_t counter_no = 0;  // 第0个计数器
     const uint8_t read_write_latch = 3;  // 0 锁存数据供CPU读；1只读写低字节；2只读写高字节；3先读写低字节，后读写高字节
     const uint8_t mode = 2;  //
+    const uint8_t BCD = 0;   // 0 二进制；1 BCD码
 
-    const uint8_t cmd = (counter_no << 6) | (read_write_latch << 4) | (mode << 1);  // 第0位为0表示二进制，为1表示BCD
+    const uint8_t cmd =
+        ((counter_no & 0x03) << 6) | ((read_write_latch & 0x03) << 4) | ((mode & 0x07) << 1) | ((BCD & 0x01) << 0);
 
-    const uint8_t i8253_cmd_port = 0x43;
-    const uint8_t i8253_data_port = 0x40 + counter_no;
+    const uint8_t i8254_cmd_port = 0x43;
+    const uint8_t i8254_data_port = 0x40 + counter_no;
 
     const uint32_t clock_rate = 1193180;
     uint16_t latch = (clock_rate + hz / 2) / hz;
 
-    outb_p(cmd, i8253_cmd_port);
-    outb_p(latch & 0xFF, i8253_data_port);
-    outb(latch >> 8, i8253_data_port);
+    // 必须先写控制命令，再写入初始计数值
+    outb_p(cmd, i8254_cmd_port);
+    outb_p((latch >> 0) & 0xFF, i8254_data_port);
+    outb_p((latch >> 8) & 0xFF, i8254_data_port);
+
+    // for (uint8_t i = 0; i < 3; i++) {
+    //     printk("i8254 counter%u value %u\n", i, read_i8254_counter(i));
+    // }
 }
diff --git a/kernel/sched.c b/kernel/sched.c
index cc0d6d0..471cd2a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -167,12 +167,12 @@ const char *task_state(unsigned int state) {
 void debug_print_all_tasks() {
     task_t *p = 0;
     list_head_t *pos = 0, *t = 0;
-    printl(MPL_TASK_TITLE, "         NAME       STATE TK/PI REASON     SCHED      KEEP");
+    printl(MPL_TASK_TITLE, "         NAME       STATE TK/PI REASON     SCHED      KEEP       TURN");
     list_for_each_safe(pos, t, &all_tasks) {
         p = list_entry(pos, task_t, list);
-        printl(MPL_TASK_0 + p->pid, "%08x%s%-6s:%u %s %02u/%02u %-10s %-10u %-10u", p,
+        printl(MPL_TASK_0 + p->pid, "%08x%s%-6s:%u %s %02u/%02u %-10s %-10u %-10u %-10u", p,
                p->state == TASK_RUNNING ? ">" : " ", p->name, p->pid, task_state(p->state), p->ticks, p->priority,
-               p->reason, p->sched_cnt, p->sched_keep_cnt);
+               p->reason, p->sched_cnt, p->sched_keep_cnt, p->turn);
     }
 }
 
@@ -188,11 +188,6 @@ void schedule() {
     unsigned long iflags;
     irq_save(iflags);
 
-    if (0 == current->ticks) {
-        current->turn++;
-        current->ticks = current->priority;
-    }
-
     if (current->state == TASK_RUNNING) {
         current->state = TASK_READY;
     }
@@ -233,10 +228,10 @@ void schedule() {
     task_t *prev = current;
     task_t *next = sel != 0 ? sel : root;
 
+    prev->need_resched = 0;
+
     next->state = TASK_RUNNING;
     next->reason = "";
-    next->ticks = 5;
-    prev->need_resched = 0;
 
     if (prev != next) {
         next->sched_cnt++;
diff --git a/kernel/setup.c b/kernel/setup.c
index 12e2314..a44c169 100644
--- a/kernel/setup.c
+++ b/kernel/setup.c
@@ -24,7 +24,7 @@ extern void init_buffer();
 extern void setup_gdt();
 extern void setup_idt();
 extern void setup_gate();
-void setup_i8253(uint16_t hz);
+void setup_i8254(uint16_t hz);
 extern void detect_cpu();
 extern void setup_sysc();
 extern void setup_pci();
@@ -87,7 +87,7 @@ void setup_kernel() {
 
     boot_delay(DEFAULT_BOOT_DELAY_TICKS);
 
-    setup_i8253(100);
+    setup_i8254(100);
     setup_irqs();
 
     void ide_init();