89 lines
2.0 KiB
C
89 lines
2.0 KiB
C
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/*
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Driver for serial output.
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Mostly useful for debug output because QEMU allows the redirection of serial output to either stdio or a file on the host computer.
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*/
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#include <types.h>
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#include <port_io.h>
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#include <string.h>
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#include <drivers/serio.h>
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#define COM1_IO_ADDR 0x3F8
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#define COM2_IO_ADDR 0x2F8
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#define COM1_IRQ 0x4
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#define COM2_IRQ 0x3
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#define COM1_LCR (COM1_IO_ADDR + 3)
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#define COM2_LCR (COM2_IO_ADDR + 3)
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#define BAUD 57600
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#define DIVISOR 2
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int serial_init(void)
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{
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/* The following is taken from https://wiki.osdev.org/Serial_Ports */
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outb(COM1_IO_ADDR + 1, 0x00); // Disable all interrupts
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outb(COM1_IO_ADDR + 3, 0x80); // Enable DLAB (set baud rate divisor)
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outb(COM1_IO_ADDR + 0, 0x03); // Set divisor to 3 (lo byte) 38400 baud
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outb(COM1_IO_ADDR + 1, 0x00); // (hi byte)
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outb(COM1_IO_ADDR + 3, 0x03); // 8 bits, no parity, one stop bit
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outb(COM1_IO_ADDR + 2, 0xC7); // Enable FIFO, clear them, with 14-byte threshold
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outb(COM1_IO_ADDR + 4, 0x0B); // IRQs enabled, RTS/DSR set
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outb(COM1_IO_ADDR + 4, 0x1E); // Set in loopback mode, test the serial chip
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outb(COM1_IO_ADDR + 0, 0xAE); // Test serial chip (send byte 0xAE and check if serial returns same byte)
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// Check if serial is faulty (i.e: not same byte as sent)
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if(inb(COM1_IO_ADDR + 0) != 0xAE)
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{
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return 1;
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}
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// If serial is not faulty set it in normal operation mode
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// (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
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outb(COM1_IO_ADDR + 4, 0x0F);
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return 0;
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}
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static int is_transmit_empty(void)
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{
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return inb(COM1_IO_ADDR + 5) & 0x20;
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}
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static int serial_received(void)
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{
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return inb(COM1_IO_ADDR + 5) & 1;
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}
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void serial_write(char a)
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{
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while (is_transmit_empty() == 0);
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outb(COM1_IO_ADDR, a);
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}
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void serial_puts(const char* s)
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{
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for (int i = 0; i < (int) strlen(s); i++)
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{
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serial_write(s[i]);
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}
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}
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char serial_read(void)
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{
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while (serial_received() == 0);
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return inb(COM1_IO_ADDR);
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}
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bool use_serial(void)
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{
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return true;
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}
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