Date: Sun, 6 Jul 2003 21:36:55 -0700 (PDT) From: wpaul@FreeBSD.ORG (Bill Paul) To: hackers@freebsd.org, mobile@freebsd.org Subject: MCT USB<->RS232 driver Message-ID: <20030707043655.71E6537B422@hub.freebsd.org>
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While wandering around CompUSA today, I came upon what I consider to be an incredibly useful little device: the Targus USB mobile port replicator with ethernet. This device is basically a multi-port USB hub with a bunch of peripherals attached, including: - PS/2 keyboard port - PS/2 mouse port - parallel printer port - RS-232 serial port - 10/100 ethernet port - Two USB 1.1 ports for any other USB devices you care to use For someone like me, who owns a 'legacy free' laptop that has no parallel or serial ports, or external keyboard/mouse ports, this struck me as a pretty clever idea. When I got it home, I found that almost everything is supported in FreeBSD 5.x, except for one thing: the serial port. The chip is a MCT USB-232 device, which is supported in NetBSD, but not FreeBSD. Not to be denied, I grabbed the umct(4) driver from NetBSD and got it working well enough that I can run userland PPP over it with my US Robotics external 56K modem. (If fact, I'm composing this e-mail over it right now.) It's not perfect. One major problem is that unlike all the other USB serial devices, this one provides incoming data via the interrupt endpoint instead of the bulk IN endpoint. Somehow in NetBSD, both the ucom(4) support module and the driver itself are able to read from the interrupt endpoint, but this trick doesn't work in FreeBSD. Consequently, I had to kludge things up to stuff data into the terminal device from the umct(4) driver's interrupt pipe handler. This is messy, but it works. It anyone else wants to use this driver, you can download it from: http://www.freebsd.org/~wpaul/MCT/mct.tar.gz To use it, download the tarball, then do the following: # cd /sys # cat /path/to/mct.tar.gz | gzip -d | tar -xvf - # cd modules/umct # make; make install; make load You need the ucom(4) module loaded as well. I'm not going to commit this yet because there's one thing I haven't been able to test, which is that I'm not sure how this device is supposed to signal changes in the modem status register. It's supposed to signal changes via the interrupt pipe, but I don't see how that can work if the interrupt pipe is also being used for incoming data. There's no easy way for me to figure it out either since I have no datasheet for this chip. In the meantime, I consider this useful enough that I should make it available for others who might have a USB<->RS232 adapter with the same chip. Share and enjoy! -Bill -- ============================================================================= -Bill Paul (510) 749-2329 | Senior Engineer, Master of Unix-Fu wpaul@windriver.com | Wind River Systems ============================================================================= "If stupidity were a handicap, you'd have the best parking spot." =============================================================================
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