---
name: "cy"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["linux", "openbsd"]
url: "https://new.carta.tech/cy"
---

# cy(4)

Cyclades Cyclom-{4, 8, 16}Y asynchronous comms board device driver

## NAME

**cy** – Cyclades Cyclom-{4, 8, 16}Y asynchronous comms board device driver

## SYNOPSIS

**cy0 at isa? iomem 0xd4000 irq 12** **cy\* at pci?**

## DESCRIPTION

This driver provides an interface to Cyclades Cyclom-4Y, Cyclom-8Y and Cyclom-16Y asynchronous multiport serial boards. These boards are based around Cirrus Logic CD1400 communication controllers.

The device minor numbers for this driver are encoded as follows:

```
    d c c u u u u u	- bits in the minor device number
    bits    meaning
    ----    -------
    uuuuu   physical serial line (i.e., unit) to use
		0-7 on a cyclom-8Y, 0-15 on a cyclom-16Y
    cc      card number
    d       dial-out flag
```

## DIAGNOSTICS

- cy0: port 0 ibuf overrun

  Incoming characters have been discarded due to a buffer overflow.

- cy0: port 0 fifo overrun

  Incoming characters have been discarded due to a CD1400 channel overrun. This is caused by interrupts not being serviced sufficiently quickly to prevent the 12 byte receive FIFO on a serial channel from overflowing. Reducing the value of the RX\_FIFO\_THRESHOLD #define from 6 to something smaller may help slow machines avoid this problem.

## SEE ALSO

[com(4)](/com/4.md), [intro(4)](/intro/4.md), [isa(4)](/isa/4.md), [pci(4)](/pci/4.md), [termios(4)](/termios/4.md), [tty(4)](/tty/4.md)

## HISTORY

Some ideas for the architecture of this driver's two-layer processing model were derived from the fas 2.10 driver by Uwe Doering ⟨*gemini@geminix.in-berlin.de*⟩ and the high-performance com driver by Bruce Evans ⟨*bde@kralizec.zeta.org.au*⟩.

This work was made possible through the donation of a Cyclom-8Y board by the manufacturer, Cyclades Corporation. However, neither Cyclades nor the author make any warranties regarding this software, nor guarantees of support.

## AUTHORS

The driver was written by Andrew Herbert ⟨*andrew@werple.apana.org.au*⟩.

## BUGS

There is currently no BREAK handling - breaks are ignored. There is no support for bad-character reporting, except via PARMRK. The Cyclom-\[48\]Y boards do not listen to the RTS signal for receiver flow control. FIFO overruns are only logged when the termios IGNPAR setting is enabled.