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x86_64: allow serial port baud rate to be configured

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This commit is contained in:
max 🍓
2023-05-07 12:22:47 +01:00
parent 9e16a2e70c
commit 96e695704a
3 changed files with 46 additions and 14 deletions
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2
arch/x86_64/include/arch/serial.h
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@@ -18,7 +18,7 @@ extern char serial_recv_byte(int device);
extern int serial_rcvd(int device);
extern void serialcon_init(void);
extern void serialcon_init(int baud);
#ifdef __cplusplus
}

2
arch/x86_64/init.c
View File

@@ -48,7 +48,7 @@ int ml_init(uintptr_t arg)
bootstrap_cpu_init();
vgacon_init();
serialcon_init();
serialcon_init(115200);
clock_calibrate(500);
print_kernel_banner();

56
arch/x86_64/serial.c
View File

@@ -49,17 +49,49 @@ void serialcon_write(struct console *con, const char *s, unsigned int len)
}
}
static void init_serial_port(int port)
static int get_baud_divisor(int baud)
{
outportb(port + 1, 0x00); // Disable all interrupts
outportb(port + 3, 0x80); // Enable DLAB (set baud rate divisor)
outportb(port + 0, 0x03); // Set divisor to 3 (lo byte) 38400 baud
outportb(port + 1, 0x00); // (hi byte)
outportb(port + 3, 0x03); // 8 bits, no parity, one stop bit
outportb(port + 2, 0xC7); // Enable FIFO, clear them, with 14-byte threshold
outportb(port + 4, 0x0B); // IRQs enabled, RTS/DSR set
outportb(port + 4, 0x1E); // Set in loopback mode, test the serial chip
outportb(port + 0, 0xAE); // Test serial chip (send byte 0xAE and check if serial returns same byte)
int freq = 115200;
int best_baud = -1;
int best_div = -1;
for (int i = 1; i < 254; i++) {
int this_baud = freq / i;
if (this_baud == baud) {
return i;
}
if (best_baud == -1) {
best_baud = this_baud;
best_div = i;
continue;
}
if (this_baud < baud && best_baud > baud) {
/* TODO pick divisor that gives the closest baud rate */
return best_div;
}
best_baud = this_baud;
best_div = i;
}
return best_div;
}
static void init_serial_port(int port, int baud)
{
int baud_div = get_baud_divisor(baud);
outportb(port + 1, 0x00); // Disable all interrupts
outportb(port + 3, 0x80); // Enable DLAB (set baud rate divisor)
outportb(port + 0, baud_div); // Set divisor
outportb(port + 1, 0x00);
outportb(port + 3, 0x03); // 8 bits, no parity, one stop bit
outportb(port + 2, 0xC7); // Enable FIFO, clear them, with 14-byte threshold
outportb(port + 4, 0x0B); // IRQs enabled, RTS/DSR set
outportb(port + 4, 0x1E); // Set in loopback mode, test the serial chip
outportb(port + 0, 0xAE); // Test serial chip (send byte 0xAE and check if serial returns same byte)
volatile unsigned int q = 0;
while (!serial_received(port)) {
@@ -85,8 +117,8 @@ static struct console serialcon = {
.c_lock = SPIN_LOCK_INIT,
};
void serialcon_init(void)
void serialcon_init(int baud)
{
init_serial_port(COM1);
init_serial_port(COM1, baud);
console_register(&serialcon);
}