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