51 lines
1.4 KiB
C
51 lines
1.4 KiB
C
#include "inttypes.h"
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#include "io.h"
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#define PORT 0x3f8 // COM1
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static int serial_initialized = 0;
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int init_serial() {
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outportb(PORT + 1, 0x00); // Disable all interrupts
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outportb(PORT + 3, 0x80); // Enable DLAB (set baud rate divisor)
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outportb(PORT + 0, 0x03); // Set divisor to 3 (lo byte) 38400 baud
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outportb(PORT + 1, 0x00); // (hi byte)
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outportb(PORT + 3, 0x03); // 8 bits, no parity, one stop bit
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outportb(PORT + 2, 0xC7); // Enable FIFO, clear them, with 14-byte threshold
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outportb(PORT + 4, 0x0B); // IRQs enabled, RTS/DSR set
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outportb(PORT + 4, 0x1E); // Set in loopback mode, test the serial chip
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outportb(PORT + 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 (inportb(PORT + 0) != 0xAE) {
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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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outportb(PORT + 4, 0x0F);
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serial_initialized = 1;
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return 0;
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}
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int serial_received() { return inportb(PORT + 5) & 1; }
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char serial_read() {
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while (serial_received() == 0)
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;
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return inportb(PORT);
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}
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int is_transmit_empty() { return inportb(PORT + 5) & 0x20; }
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void serial_write(char a) {
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if (!serial_initialized) {
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return;
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}
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while (is_transmit_empty() == 0)
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;
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outportb(PORT, a);
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}
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