Serial port type detection

[mjs]

Hi,

I found some old sources from me where I detect the IRQ and the type (8250, 16450, 16550, 16550A) of a COM port. I converted the sources to the ReactOS style.

The detection if there is a COM port at all is made by inverting all bits of the LCR twice:

Code: Select all

BYTE Lcr, TestLcr;
BYTE OldScr, Scr5A, ScrA5;
BOOLEAN FifoEnabled;
BYTE NewFifoStatus;

Lcr = READ_PORT_UCHAR(SER_LCR(BaseAddress));
WRITE_PORT_UCHAR(BaseAddress, (BYTE) (Lcr ^ 0xFF));
TestLcr = (BYTE) (READ_PORT_UCHAR(SER_LCR(BaseAddress)) ^ 0xFF);
WRITE_PORT_UCHAR(BaseAddress, Lcr);

/* Accessing the LCR must work for a usable serial port */
if (TestLcr!=Lcr)
  return SER_TYPE_NONE;

/* Ensure that all following accesses are done as required */
READ_PORT_UCHAR(SER_RBR(BaseAddress));
READ_PORT_UCHAR(SER_IER(BaseAddress));
READ_PORT_UCHAR(SER_IIR(BaseAddress));
READ_PORT_UCHAR(SER_LCR(BaseAddress));
READ_PORT_UCHAR(SER_MCR(BaseAddress));
READ_PORT_UCHAR(SER_LSR(BaseAddress));
READ_PORT_UCHAR(SER_MSR(BaseAddress));
READ_PORT_UCHAR(SER_SCR(BaseAddress));

/* Test scratch pad */
OldScr = READ_PORT_UCHAR(SER_SCR(BaseAddress));
WRITE_PORT_UCHAR(SER_SCR(BaseAddress), 0x5A);
Scr5A = READ_PORT_UCHAR(SER_SCR(BaseAddress));
WRITE_PORT_UCHAR(SER_SCR(BaseAddress), 0xA5);
ScrA5 = READ_PORT_UCHAR(SER_SCR(BaseAddress));
WRITE_PORT_UCHAR(SER_SCR(BaseAddress), OldScr);

/* When non-functional, we have a 8250 */
if (Scr5A!=0x5A || ScrA5!=0xA5)
  return SER_TYPE_8250;

FifoEnabled = (READ_PORT_UCHAR(SER_IIR(BaseAddress)) & 0x80)!=0;
WRITE_PORT_UCHAR(SER_FCR(BaseAddress), SR_FCR_ENABLE_FIFO);
NewFifoStatus = READ_PORT_UCHAR(SER_IIR(BaseAddress)) & 0xC0;
if (!FifoEnabled)
  WRITE_PORT_UCHAR(SER_FCR(BaseAddress), 0);
switch (NewFifoStatus) {
case 0x00:
  return SER_TYPE_16450;
case 0x80:
  return SER_TYPE_16550;
}

return SER_TYPE_16550A;

I hope it's of some use for you ...

Regards,
Mark

[uniQ]

I found some old sources from me

Wait, you mean, you wrote this a while ago and re-discovered it?

-uniQ

[mjs]

While keeping my ReactOS copy up-to-date with SVN (and reading the log-messages), I saw that there was made some work creating a serial port driver and I remembered that I wrote the port type and IRQ detection for serial ports a long time ago (several years) in PowerBASIC. I thought this could be interesting for the ReactOS developer that works on the serial port driver, so I translated parts of my sources to C using the standard ReactOS driver development macros.

The problem was that the sources were so old that I had to search for them - and I found them as you might assume.

Maybe you want to see the old BASIC (PowerBASIC + inline assembler) sources?

Regards,
Mark

[uniQ]

Maybe you want to see the old BASIC (PowerBASIC + inline assembler) sources?

I'll leave that for the relevant Commission.

-uniQ