libftdi Archives

Subject: Re: Hi-speed UARTs (3Mbps to 12Mbps) on FT2232H/FT4232H

From: Emmanuel Blot <>
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Date: Wed, 19 May 2010 00:08:32 +0200
> Thanks for your patch! Some small questions:

> - FTDI_BAUDRATE_TOLERANCE doesn't seem to get used?

Yeah, sorry, I failed to copy the whole patch.
I'll submit a new version.

> - Could you check if this piece of code doesn't break
>  the bitbang mode as it multiplies the baud rate by four:
> +        if ( baudrate > (FTDI_BAUDRATE_REF_CLOCK>>1) )
> +        {
> +            ref_clock *= 4; // 12 MHz
> +            hispeed = 1;
> +        }

Would you have a sample test file to exercise this mode, so I could
check with an oscilloscope?
I don't know how to test the bitbang mode otherwise (I'm using FTDI
2232H/4232H with UART, SPI and JTAG, but I do not use the bitbang

> - Where does this "magic" come from: "*index |= 1<<9; // use hispeed mode"?

Reverse-engineering of the official Windows driver.
I have no idea about the official name for this bit ;-)

>  Maybe a #define would be nice to give it a concrete name.

I do agree, but I'm not sure how to name it.

BTW, I've noticed that a couple of comments would need some clean up,
as the code has evolved since the first versions of libftdi but the
comments often refer to the oldest FTDI chips only.


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