Forgot to reply to all. ---------- Forwarded message ---------- From: Matt Schulte <matts@xxxxxxxxxxxxxxxxxxxx> Date: Wed, Oct 17, 2012 at 2:10 PM Subject: Re: New serial card development To: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> On Mon, Oct 15, 2012 at 6:26 PM, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote: >> That sounds reasonable but I am not sure what you mean my the "method >> documented in the Exar data sheet." I've been through this thing >> quite a bit and I don't see anything about how one might detect the >> ports without the PCI id numbers. Could you explain what you mean by >> this? > > I don't believe you can identify the new Exars except by PCI id - which > is fine as the type can be passed via the 8250_pci driver. > >> * This new Exar UART does not use a crystal it uses a clock from the >> PCI Express bus. Also it has a fractional divisor that gets them >> 1/16th (0.0625) resolution on their divisors. The normal DLL and DLM >> registers contain the integer part of the divisor and the DLD register >> provides the fractional component. The divisor is able to be set to >> anything between 1 and (2^16 - 0.0625) in increments of 0.0625. > > That probably needs a bit of tweaking to getthe best results Does this make you lean one way or the other in how I would best implement this driver? >> * These UARTs have 256 byte FIFOs per port per direction. I would >> like to utilize these to their fullest potential. > > We already handle other similar fifos so again in theory you just need to > set the size and it works. Good, I'm sure it will be fine ;) >> * I need to toggle 16-bit general purpose IO signals to control two >> things on my card: Receive Echo Cancel (useful for 2-wire 485) and the >> selectable termination resistance on my receiver chips. > > Ok - we don't have a generalized way of doing that in the RS485 bits but > anything liek this should get added generically (in case other chips want > to do it) I have two features, one that could be considered part of RS485 and one that has nothing at all to do with RS485. >> * I need to change two UART specific registers to change the sampling >> mode (16x, 8x and 4x). > > What determines this. User would have to decide to turn on non-standard 8x or 4x sampling mode. >> * I need to figure out if the new RS485 elements that have been added >> to 8250 can be used on these Exar parts and if not I need something >> that can enable RS485 for us. > > They should provide the basics. Where will I take the built in 485 flags and turn them into whatever my board needs? >> * I need to be able to enable 9-bit mode, what they call Normal >> Multi-drop as well as the Auto Address Detection Mode used in >> conjunction with the Multi-drop mode. > > That may actually be the most "fun" bit - the entire Linux tty layer is > devoutly 5-8bit, although people do some horrible hacks with "8 plus > parity". Transmitting is a little bit interesting but manageable. In the receive direction the chip can detect the 9th bit and recognize it as an address bit and then check that byte against a preset station address that has been specified by the user. >> With this laundry list of items that I would like to include, do you >> still feel like this is something that should be included in the >> kernel's 8250.c/8250_pci.c drivers? > > I think so. It's also the path that lets you do basic enabling, get > it working upstream and then extend as is needed for the other features. So is there an example of a device already in the kernel that you think I should try to emulate? Will I be best served with something like 8250_dw.c or do you think I should try to get all of my things directly into 8250 and 8250_pci? Matt Schulte -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
