October 2, 1998 NTWOC 4

### NAME

ntwoc - Riscom/N2, N2pci, WANic 400 synchronous serial interfaces

### SYNOPSIS

ntwoc* at pci? dev ? function ? flags 0 ntwoc0 at isa? port 0x300 irq 5 iomem 0xc8000 flags 1

### DESCRIPTION

The ntwoc device driver supports bit-synchronous serial communication using Cisco HDLC framing. The cards are capable of being driven by the line clock or from an internal baud rate generator. The devices all use the Hitachi hd64570 serial chip. The hd64570 supports 2 asynchronous/byte-synchronous/bit-synchronous serial ports, and has a 4-channel DMA controller for loading the serial port FIFOs.

The ISA Riscom/N2 card has a jumper block to set the IRQ and a DIP switch to set the port address the card will use. The values programmed into the card must be specified with the port and irq locators in the kernel configuration line. The iomem locator must be specified and must occur on a 16k boundary. The driver uses a 16k region of io memory. Bit 0 of the flags locator indicates if there is a second serial port available on the card.

Currently clock source and speed information is specified with the flags locator in the kernel configuration file. The flags field has the following format. ``

      3                   2                   1
    1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
    +-------------+ +-----+ +-----+ + +---+ +-+     + +---+ +-+   +
          tmc         tdiv    rdiv  e1 rxs1 ts1    e0 rxs0  txs0  np(*)

tmc
  Defines the timer constant. The base clock frequency is divided by tmc to generate the main clock for receiving and sending. Further division is possible with the tdiv and rdiv divisor options. A value of 0 is treated as 256.

tdiv
  Defines the transmit divisor as 2^(tdiv). The internal transmit clock frequency is determined by dividing the base clock frequency by tmc and then dividing by 2^(tdiv).

rdiv
  Defines the receive divisor as 2^(rdiv). The internal receive clock frequency is determined by dividing the base clock frequency by tmc and then dividing by 2^(rdiv).

e0 e1
  If true the internal clock source is used to drive the line clock for port 0 or port 1 respectively.

rxs0 rxs1
  Specifies which clock source to use for receiving data on port 0 and port 1 respectively. The following values are accepted:

  0
    Line clock.
  1
    Line clock with noise suppression.
  2
    Internal clock.

txs0 txs1
  Specifies which clock source to use for transmitting data on port 0 and port 1 respectively. The following values are accepted:

  0
    Line clock.
  1
    Internal clock.
  2
    Receive clock.

np
  (For the ISA card only) A value of 1 indicates there is a second serial port present on the card. This is auto-detected on the PCI card and need not be specified.

### HARDWARE

Cards supported by the ntwoc driver include:

  SDL Communications Riscom/N2
  SDL Communications N2pci
  SDL Communications WANic 400 (untested)

### DIAGNOSTICS

ntwoc0: TXDMA underrun - fifo depth maxed
  Indicates that the serial port's FIFO is being drained faster than DMA can fill it. The driver automatically increases the low-water mark at which to begin DMA transfers when underruns occur. This diagnostic is issued when the low-water mark is maximized (i.e., 1 less than the depth of the FIFO).

ntwoc0: RXDMA buffer overflow
  Indicates that a frame is being received by the card, but there are no free receive buffers.

### SEE ALSO

intro(4), isa(4), pci(4), ifconfig(8)

### HISTORY

The PCI driver first appeared in NetBSD1.4. Much of the ISA driver was adapted from the FreeBSD sr driver and first appeared in NetBSD1.5.

### BUGS

Use of the flags locator for setting the clock sources and speeds should be replaced with ioctl's and a control program.