Kernel CAPI Interface to Hardware Drivers ----------------------------------------- 1. Overview From the CAPI 2.0 specification: COMMON-ISDN-API (CAPI) is an application programming interface standard used to access ISDN equipment connected to basic rate interfaces (BRI) and primary rate interfaces (PRI). Kernel CAPI operates as a dispatching layer between CAPI applications and CAPI hardware drivers. Hardware drivers register ISDN devices (controllers, in CAPI lingo) with Kernel CAPI to indicate their readiness to provide their service to CAPI applications. CAPI applications also register with Kernel CAPI, requesting association with a CAPI device. Kernel CAPI then dispatches the application registration to an available device, forwarding it to the corresponding hardware driver. Kernel CAPI then forwards CAPI messages in both directions between the application and the hardware driver. Format and semantics of CAPI messages are specified in the CAPI 2.0 standard. This standard is freely available from http://www.capi.org. 2. Driver and Device Registration CAPI drivers optionally register themselves with Kernel CAPI by calling the Kernel CAPI function register_capi_driver() with a pointer to a struct capi_driver. This structure must be filled with the name and revision of the driver, and optionally a pointer to a callback function, add_card(). The registration can be revoked by calling the function unregister_capi_driver() with a pointer to the same struct capi_driver. CAPI drivers must register each of the ISDN devices they control with Kernel CAPI by calling the Kernel CAPI function attach_capi_ctr() with a pointer to a struct capi_ctr before they can be used. This structure must be filled with the names of the driver and controller, and a number of callback function pointers which are subsequently used by Kernel CAPI for communicating with the driver. The registration can be revoked by calling the function detach_capi_ctr() with a pointer to the same struct capi_ctr. Before the device can be actually used, the driver must fill in the device information fields 'manu', 'version', 'profile' and 'serial' in the capi_ctr structure of the device, and signal its readiness by calling capi_ctr_ready(). From then on, Kernel CAPI may call the registered callback functions for the device. If the device becomes unusable for any reason (shutdown, disconnect ...), the driver has to call capi_ctr_reseted(). This will prevent further calls to the callback functions by Kernel CAPI. 3. Application Registration and Communication Kernel CAPI forwards registration requests from applications (calls to CAPI operation CAPI_REGISTER) to an appropriate hardware driver by calling its register_appl() callback function. A unique Application ID (ApplID, u16) is allocated by Kernel CAPI and passed to register_appl() along with the parameter structure provided by the application. This is analogous to the open() operation on regular files or character devices. After a successful return from register_appl(), CAPI messages from the application may be passed to the driver for the device via calls to the send_message() callback function. The CAPI message to send is stored in the data portion of an skb. Conversely, the driver may call Kernel CAPI's capi_ctr_handle_message() function to pass a received CAPI message to Kernel CAPI for forwarding to an application, specifying its ApplID. Deregistration requests (CAPI operation CAPI_RELEASE) from applications are forwarded as calls to the release_appl() callback function, passing the same ApplID as with register_appl(). After return from release_appl(), no CAPI messages for that application may be passed to or from the device anymore. 4. Data Structures 4.1 struct capi_driver This structure describes a Kernel CAPI driver itself. It is used in the register_capi_driver() and unregister_capi_driver() functions, and contains the following non-private fields, all to be set by the driver before calling register_capi_driver(): char name[32] the name of the driver, as a zero-terminated ASCII string char revision[32] the revision number of the driver, as a zero-terminated ASCII string int (*add_card)(struct capi_driver *driver, capicardparams *data) a callback function pointer (may be NULL) 4.2 struct capi_ctr This structure describes an ISDN device (controller) handled by a Kernel CAPI driver. After registration via the attach_capi_ctr() function it is passed to all controller specific lower layer interface and callback functions to identify the controller to operate on. It contains the following non-private fields: - to be set by the driver before calling attach_capi_ctr(): struct module *owner pointer to the driver module owning the device void *driverdata an opaque pointer to driver specific data, not touched by Kernel CAPI char name[32] the name of the controller, as a zero-terminated ASCII string char *driver_name the name of the driver, as a zero-terminated ASCII string int (*load_firmware)(struct capi_ctr *ctrlr, capiloaddata *ldata) (optional) pointer to a callback function for sending firmware and configuration data to the device void (*reset_ctr)(struct capi_ctr *ctrlr) pointer to a callback function for performing a reset on the device, releasing all registered applications void (*register_appl)(struct capi_ctr *ctrlr, u16 applid, capi_register_params *rparam) void (*release_appl)(struct capi_ctr *ctrlr, u16 applid) pointers to callback functions for registration and deregistration of applications with the device u16 (*send_message)(struct capi_ctr *ctrlr, struct sk_buff *skb) pointer to a callback function for sending a CAPI message to the device char *(*procinfo)(struct capi_ctr *ctrlr) pointer to a callback function returning the entry for the device in the CAPI controller info table, /proc/capi/controller read_proc_t *ctr_read_proc pointer to the read_proc callback function for the device's proc file system entry, /proc/capi/controllers/; will be called with a pointer to the device's capi_ctr structure as the last (data) argument - to be filled in before calling capi_ctr_ready(): u8 manu[CAPI_MANUFACTURER_LEN] value to return for CAPI_GET_MANUFACTURER capi_version version value to return for CAPI_GET_VERSION capi_profile profile value to return for CAPI_GET_PROFILE u8 serial[CAPI_SERIAL_LEN] value to return for CAPI_GET_SERIAL 5. Lower Layer Interface Functions (declared in ) void register_capi_driver(struct capi_driver *drvr) void unregister_capi_driver(struct capi_driver *drvr) register/unregister a driver with Kernel CAPI int attach_capi_ctr(struct capi_ctr *ctrlr) int detach_capi_ctr(struct capi_ctr *ctrlr) register/unregister a device (controller) with Kernel CAPI void capi_ctr_ready(struct capi_ctr *ctrlr) void capi_ctr_reseted(struct capi_ctr *ctrlr) signal controller ready/not ready void capi_ctr_suspend_output(struct capi_ctr *ctrlr) void capi_ctr_resume_output(struct capi_ctr *ctrlr) signal suspend/resume void capi_ctr_handle_message(struct capi_ctr * ctrlr, u16 applid, struct sk_buff *skb) pass a received CAPI message to Kernel CAPI for forwarding to the specified application 6. Helper Functions and Macros Library functions (from ): void capilib_new_ncci(struct list_head *head, u16 applid, u32 ncci, u32 winsize) void capilib_free_ncci(struct list_head *head, u16 applid, u32 ncci) void capilib_release_appl(struct list_head *head, u16 applid) void capilib_release(struct list_head *head) void capilib_data_b3_conf(struct list_head *head, u16 applid, u32 ncci, u16 msgid) u16 capilib_data_b3_req(struct list_head *head, u16 applid, u32 ncci, u16 msgid) Macros to extract/set element values from/in a CAPI message header (from ): Get Macro Set Macro Element (Type) CAPIMSG_LEN(m) CAPIMSG_SETLEN(m, len) Total Length (u16) CAPIMSG_APPID(m) CAPIMSG_SETAPPID(m, applid) ApplID (u16) CAPIMSG_COMMAND(m) CAPIMSG_SETCOMMAND(m,cmd) Command (u8) CAPIMSG_SUBCOMMAND(m) CAPIMSG_SETSUBCOMMAND(m, cmd) Subcommand (u8) CAPIMSG_CMD(m) - Command*256 + Subcommand (u16) CAPIMSG_MSGID(m) CAPIMSG_SETMSGID(m, msgid) Message Number (u16) CAPIMSG_CONTROL(m) CAPIMSG_SETCONTROL(m, contr) Controller/PLCI/NCCI (u32) CAPIMSG_DATALEN(m) CAPIMSG_SETDATALEN(m, len) Data Length (u16)