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I'll preface this by saying that it's very possible that I've totally misunderstood how this all works.
As I understand it from reading https://wiki.osdev.org/Serial_Ports#Port_Addresses, it's possible that not even COM1 may exist, and so it's recommended to always test a port via loopback and the "scratch pad register". There's some example code further down the page that appears to do this:
#define PORT 0x3f8 // COM1
static int init_serial() {
outb(PORT + 1, 0x00); // Disable all interrupts
outb(PORT + 3, 0x80); // Enable DLAB (set baud rate divisor)
outb(PORT + 0, 0x03); // Set divisor to 3 (lo byte) 38400 baud
outb(PORT + 1, 0x00); // (hi byte)
outb(PORT + 3, 0x03); // 8 bits, no parity, one stop bit
outb(PORT + 2, 0xC7); // Enable FIFO, clear them, with 14-byte threshold
outb(PORT + 4, 0x0B); // IRQs enabled, RTS/DSR set
outb(PORT + 4, 0x1E); // Set in loopback mode, test the serial chip
outb(PORT + 0, 0xAE); // Test serial chip (send byte 0xAE and check if serial returns same byte)
// Check if serial is faulty (i.e: not same byte as sent)
if(inb(PORT + 0) != 0xAE) {
return 1;
}
// If serial is not faulty set it in normal operation mode
// (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
outb(PORT + 4, 0x0F);
return 0;
}I was thinking it might be nice if this crate, rather than marking SerialPort::new as unsafe, instead rolled init into new (I don't see that there would ever be a reason not to call init?), and that it does the loopback + scratch pad register test. new could then return a Result depending on the outcome.
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