[kernel] Let endpoints get interrupt notifications

- Add a tag field to all endpoint messages, which doubles as a
  notification field
- Add a endpoint_bind_irq syscall to enable an endpoint to listen for
  interrupt notifications. This mechanism needs to change.
- Add a temporary copy of the serial port code to nulldrv, and let it
  take responsibility for COM2

src/drivers/nulldrv/io.cpp

@@ -0,0 +1,22 @@
+#include "io.h"
+
+uint8_t
+inb(uint16_t port)
+{
+	uint8_t val;
+	__asm__ __volatile__ ( "inb %1, %0" : "=a"(val) : "Nd"(port) );
+	return val;
+}
+
+void
+outb(uint16_t port, uint8_t val)
+{
+	__asm__ __volatile__ ( "outb %0, %1" :: "a"(val), "Nd"(port) );
+}
+
+void
+io_wait(unsigned times)
+{
+	for (unsigned i = 0; i < times; ++i)
+		outb(0x80, 0);
+}

src/drivers/nulldrv/io.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <stdint.h>
+
+extern "C" {
+
+/// Read a byte from an IO port.
+/// \arg port  The address of the IO port
+/// \returns   One byte read from the port
+uint8_t inb(uint16_t port);
+
+/// Write a byte to an IO port.
+/// \arg port  The addres of the IO port
+/// \arg val   The byte to write
+void outb(uint16_t port, uint8_t val);
+
+/// Pause briefly by doing IO to port 0x80
+/// \arg times  Number of times to delay by writing
+void io_wait(unsigned times = 1);
+
+}
+
+constexpr uint16_t COM1 = 0x03f8;
+constexpr uint16_t COM2 = 0x02f8;

src/drivers/nulldrv/main.cpp

@@ -7,6 +7,9 @@
 
 #include <j6libc/syscalls.h>
 
+#include "io.h"
+#include "serial.h"
+
 char inbuf[1024];
 j6_handle_t endp = j6_handle_invalid;
 
@@ -24,7 +27,8 @@ thread_proc()
 
 	char buffer[512];
 	size_t len = sizeof(buffer);
-	j6_status_t result = _syscall_endpoint_receive(endp, &len, (void*)buffer);
+	j6_tag_t tag = 0;
+	j6_status_t result = _syscall_endpoint_receive(endp, &tag, &len, (void*)buffer);
 	if (result != j6_status_ok)
 		_syscall_thread_exit(result);
 
@@ -34,7 +38,8 @@ thread_proc()
 		if (buffer[i] >= 'A' && buffer[i] <= 'Z')
 			buffer[i] += 0x20;
 
-	result = _syscall_endpoint_send(endp, len, (void*)buffer);
+	tag++;
+	result = _syscall_endpoint_send(endp, tag, len, (void*)buffer);
 	if (result != j6_status_ok)
 		_syscall_thread_exit(result);
 
@@ -66,8 +71,8 @@ main(int argc, const char **argv)
 		return 1;
 
 	uint64_t *vma_ptr = reinterpret_cast<uint64_t*>(base);
-	for (int i = 0; i < 300; ++i)
-		vma_ptr[i] = uint64_t(i);
+	for (int i = 0; i < 3; ++i)
+		vma_ptr[i*100] = uint64_t(i);
 
 	_syscall_system_log("main thread wrote to memory area");
 
@@ -85,10 +90,14 @@ main(int argc, const char **argv)
 
 	char message[] = "MAIN THREAD SUCCESSFULLY CALLED SENDRECV IF THIS IS LOWERCASE";
 	size_t size = sizeof(message);
-	result = _syscall_endpoint_sendrecv(endp, &size, (void*)message);
+	j6_tag_t tag = 16;
+	result = _syscall_endpoint_sendrecv(endp, &tag, &size, (void*)message);
 	if (result != j6_status_ok)
 		return result;
 
+	if (tag != 17)
+		_syscall_system_log("GOT WRONG TAG FROM SENDRECV");
+
 	_syscall_system_log(message);
 
 	_syscall_system_log("main thread waiting on child");
@@ -97,6 +106,29 @@ main(int argc, const char **argv)
 	if (result != j6_status_ok)
 		return result;
 
+	_syscall_system_log("main testing irqs");
+
+	_syscall_endpoint_bind_irq(endp, 3);
+
+	serial_port com2(COM2);
+
+	const char *fgseq = "\x1b[2J";
+	while (*fgseq)
+		com2.write(*fgseq++);
+
+	for (int i = 0; i < 10; ++i)
+		com2.write('%');
+
+	size_t len = 0;
+	while (true) {
+		result = _syscall_endpoint_receive(endp, &tag, &len, nullptr);
+		if (result != j6_status_ok)
+			return result;
+
+		if (j6_tag_is_irq(tag))
+			_syscall_system_log("main thread got irq!");
+	}
+
 	_syscall_system_log("main thread closing endpoint");
 
 	result = _syscall_endpoint_close(endp);

src/drivers/nulldrv/serial.cpp

@@ -0,0 +1,41 @@
+#include "io.h"
+#include "serial.h"
+
+
+serial_port::serial_port() :
+	m_port(0)
+{
+}
+
+serial_port::serial_port(uint16_t port) :
+	m_port(port)
+{
+	outb(port + 1, 0x00);  // Disable all interrupts
+	outb(port + 3, 0x80);  // Enable the Divisor Latch Access Bit
+	outb(port + 0, 0x01);  // Divisor low bit: 1 (115200 baud)
+	outb(port + 1, 0x00);  // Divisor high bit
+	outb(port + 3, 0x03);  // 8-N-1
+	outb(port + 2, 0xe7);  // Clear and enable FIFO, enable 64 byte, 56 byte trigger
+	outb(port + 4, 0x0b);  // Data terminal ready, Request to send, aux output 2 (irq enable)
+	outb(port + 1, 0x03);  // Enable interrupts
+}
+
+bool serial_port::read_ready() { return (inb(m_port + 5) & 0x01) != 0; }
+
+bool serial_port::write_ready() {
+	uint8_t lsr = inb(m_port + 5);
+	return (lsr & 0x20) != 0;
+}
+
+char
+serial_port::read() {
+	while (!read_ready());
+	return inb(m_port);
+}
+
+void
+serial_port::write(char c) {
+	while (!write_ready());
+	outb(m_port, c);
+}
+

src/drivers/nulldrv/serial.h

@@ -0,0 +1,26 @@
+#pragma once
+/// \file serial.h
+/// Declarations related to serial ports.
+#include <stdint.h>
+
+#define serial_port nulldrv_serial_port
+
+class serial_port
+{
+public:
+	/// Constructor.
+	/// \arg port   The IO address of the serial port
+	serial_port(uint16_t port);
+
+	serial_port();
+
+	void write(char c);
+	char read();
+
+private:
+	uint16_t m_port;
+
+	bool read_ready();
+	bool write_ready();
+};
+