124 lines
3.3 KiB
C
124 lines
3.3 KiB
C
#include <stdint.h>
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#include <stddef.h>
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#include <string.h>
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#include <kernel/serial.h>
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#include "io.h"
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/* I/O ports */
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/**
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* All the I/O ports are calculated relative to their base.
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* The ports (COM1, COM2, etc) have their ports in the same order,
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* but they start at different values.
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*/
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#define SERIAL_COM1_BASE 0x3F8
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#define SERIAL_DATA_PORT(base) (base)
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#define SERIAL_FIFO_COMMAND_PORT(base) (base + 2)
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#define SERIAL_LINE_COMMAND_PORT(base) (base + 3)
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#define SERIAL_MODEM_COMMAND_PORT(base) (base + 4)
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#define SERIAL_LINE_STATUS_PORT(base) (base + 5)
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/* I/O port commands */
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/**
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* SERIAL_LINE_ENABLE_DLAB:
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* Tells the serial port to expect first the highest 8 bits on the data port,
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* then the lowest 8 bits will follow
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*/
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#define SERIAL_LINE_ENABLE_DLAB 0x80
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void serial_configure_baud_rate(unsigned short com, unsigned short divisor)
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{
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outb(SERIAL_LINE_COMMAND_PORT(com),
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SERIAL_LINE_ENABLE_DLAB);
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outb(SERIAL_DATA_PORT(com),
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(divisor >> 8) & 0x00FF);
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outb(SERIAL_DATA_PORT(com),
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divisor & 0x00FF);
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}
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void serial_configure_line(unsigned short com)
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{
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/**
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* Bit: | 7 | 6 | 5 4 3 | 2 | 1 0 |
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* Content: | d | b | prty | s | dl |
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* d - Enabled (d = 1) or disables (d = 0) DLAB
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* b - If break control is enabled (b = 1) or disabled (b = 0)
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* prty - The number of parity bits to use
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* s - The number of stop bits to use (s = 0 equals 1, s = 1 equals 1.5 or 2)
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* dl - Describes the length of the data
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* Value: | 0 | 0 | 0 0 0 | 0 | 1 1 | = 0x03
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*/
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outb(SERIAL_LINE_COMMAND_PORT(com), 0x03);
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}
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void serial_configure_buffers(unsigned short com)
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{
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/**
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* Bit: | 7 6 | 5 | 4 | 3 | 2 | 1 | 0 |
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* Content: | lvl | bs | r | dma | clt | clr | e |
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* lvl - How many bytes should be stored in the FIFO buffers
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* bs - If the buffers should be 16 or 64 bytes large
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* r - Reserved for future use
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* dma - How the serial port data should be accessed
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* clt - Clear the transmission FIFO buffer
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* clr - Clear the receiver FIFO buffer
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* e - If the FIFO buffer should be enabled or not
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* Value: | 1 1 | 0 | 0 | 0 | 1 | 1 | 1 |
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*/
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outb(SERIAL_FIFO_COMMAND_PORT(com), 0xC7);
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}
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void serial_configure_modem(unsigned short com)
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{
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/**
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* Bit: | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
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* Content: | r | r | af | lb | ao2 | ao1 | rts | dtr |
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* r - Reserved
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* af - Autoflow control enabled
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* lb - Loopback mode (used for debugging serial ports)
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* ao2 - Auxiliary output 2, used for receiving interrupts
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* ao1 - Auxiliary output 1
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* rts - Ready to transmit
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* dtr - Data Terminal ready
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* Value: | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
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*/
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outb(SERIAL_MODEM_COMMAND_PORT(com), 0x03);
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}
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int serial_is_transmit_fifo_empty(unsigned int com)
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{
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/* 0x20 = 0010 0000 */
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return inb(SERIAL_LINE_STATUS_PORT(com)) & 0x20;
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}
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void serial_initialize(void)
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{
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serial_configure_baud_rate(SERIAL_COM1_BASE, 2);
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serial_configure_line(SERIAL_COM1_BASE);
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serial_configure_buffers(SERIAL_COM1_BASE);
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serial_configure_modem(SERIAL_COM1_BASE);
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}
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void serial_write_byte(unsigned short com, char c)
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{
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while (!serial_is_transmit_fifo_empty(com));
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outb(SERIAL_DATA_PORT(com), c);
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}
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void serial_write(const char* buf, size_t len)
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{
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for (size_t i = 0; i < len; i++)
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serial_write_byte(SERIAL_COM1_BASE, buf[i]);
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}
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void serial_writestring(const char* buf)
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{
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serial_write(buf, strlen(buf));
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}
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