The digi driver provides support for DigiBoard PC/Xe and PC/Xi series intelligent serial multiport cards with asynchronous interfaces based on the EIA RS-232C ( CCITT V.24) standard.
Input and output for each line may set to one of following baud rates; 50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200, 38400, 57600, or for newer versions of cards 115200.
The driver does not use any interrupts, it is "polling-based". This means that it uses clock interrupts instead of interrupts generated by DigiBoard cards and checks the state of cards 25 times per second. This is practical because the DigiBoard cards have large input and output buffers (more than 1Kbyte per port) and hardware that allows efficiently finding the port that needs attention. The only problem seen with this policy is slower SLIP and PPP response.
Each line in the kernel configuration file describes one card, not one port as in the sio(4) driver.
The flags keyword may be used on each ""device dgb"" line in the kernel configuration file to change the pinout of the interface or to use new PC/Xe cards which can work with an 8K memory window in compatibility mode (with a 64K memory window). Note that using 8K memory window does not mean shorter input/output buffers, it means only that all buffers will be mapped to the same memory address and switched as needed.
The port value must be the same as the port set on the card by jumpers. For PC/Xi cards the same rule is applicable to the iomem value. It must be the same as the memory address set on the card by jumpers. For PC/Xe cards there is no need to use jumpers for this purpose. In fact there are no jumpers to do it. Just write the address you want as the iomem value in kernel config file and the card will be programmed to use this address.
The same range of memory addresses may be used for all the DigiBoards installed (but not for any other card or real memory). DigiBoards with a large amount of memory (256K or 512K and perhaps even 128K) must be mapped to memory addresses outside of the first megabyte. If the computer has more than 15 megabytes of memory then there is no free address space outside of the first megabyte where such DigiBoards can be mapped. In this case you may need to reduce the amount of memory in the computer. But many machines provide a better solution. They have the ability to ""turn off"" the memory in the 16th megabyte (addresses 0xF00000 - 0xFFFFFF) using the BIOS setup. Then the DigiBoards address space can be set to this "hole".
Serial ports controlled by the digi driver can be used for both "callin" and "callout". For each port there is a callin device and a callout device. The minor number of the callout device is 128 higher than that of the corresponding callin port. The callin device is general purpose. Processes opening it normally wait for carrier and for the callout device to become inactive. The callout device is used to steal the port from processes waiting for carrier on the callin device. Processes opening it do not wait for carrier and put any processes waiting for carrier on the callin device into a deeper sleep so that they do not conflict with the callout session. The callout device is abused for handling programs that are supposed to work on general ports and need to open the port without waiting but are too stupid to do so.
The digi driver also supports an initial-state and a lock-state control device for each of the callin and the callout "data" devices. The minor number of the initial-state device is 32 higher than that of the corresponding data device. The minor number of the lock-state device is 64 higher than that of the corresponding data device. The termios settings of a data device are copied from those of the corresponding initial-state device on first opens and are not inherited from previous opens. Use stty(1) in the normal way on the initial-state devices to program initial termios states suitable for your setup.
The lock termios state acts as flags to disable changing the termios state. E.g., to lock a flag variable such as CRTSCTS, use ""stty crtscts"" on the lock-state device. Speeds and special characters may be locked by setting the corresponding value in the lock-state device to any nonzero value.
Correct programs talking to correctly wired external devices work with almost arbitrary initial states and no locking, but other setups may benefit from changing some of the default initial state and locking the state. In particular, the initial states for non (POSIX) standard flags should be set to suit the devices attached and may need to be locked to prevent buggy programs from changing them. E.g., CRTSCTS should be locked on for devices that support RTS/CTS handshaking at all times and off for devices that do not support it at all. CLOCAL should be locked on for devices that do not support carrier. HUPCL may be locked off if you do not want to hang up for some reason. In general, very bad things happen if something is locked to the wrong state, and things should not be locked for devices that support more than one setting. The CLOCAL flag on callin ports should be locked off for logins to avoid certain security holes, but this needs to be done by getty if the callin port is used for anything else.