unleashed-firmware/wiki/fw/FURI.md

Flipper Universal Registry Implementation or FURI is important part of Flipper firmware. It is used to:

• application control (start, exit, switch between active)
• data exchange between application (create/open channel, subscribe and push messages or read/write values)
• non-volatile data storage for application (create/open value and read/write)

Application registry and control (FURIAC)

Start and change application wrokflow

• FuriApp furiac_start(void(app*)(void*), char* name, void* param) simply starts application. It call app entrypoint with param passed as argument. Useful for daemon applications and pop-up.
• FuriApp furiac_switch(void(app*)(void*), char* name, void* param) swtich to other application. FURI stop current app, call app entrypoint with param passed as argument and save current application entrypoint to prev field in current application registry. Useful for UI or "active" application.

Exit application

• furiac_exit(void* param) stop current application (stop thread and clear application's stack), start application from prev entry in current application registry, cleanup current application registry.
• furiac_kill(FuriApp app) stop specified app without returning to prev application.

Data exchange

• FuriRecord furi_create(char* name) creates named FURI record. Returns NULL if registry have not enough memory for creating.
• FuriRecord furi_open(char* name, bool solo, bool no_mute) opens existing FURI record by name. Returns NULL if record does not exist. If solo is true another applications handlers set into "muted" state. When appication has exited or record has closed, all handlers is unmuted. It may be useful for concurrently acces to resources like framebuffer or beeper. If no_mute is true, another applications cannot mute this handler.
• bool furi_close(FuriRecord record) close handler and unmute anothers.
• bool furi_read(FuriRecord record, void* data, size_t size) read message from record. Returns true if success, false otherwise.
• bool furi_write(FuriRecord record, const void* data, size_t size) write message to record. Returns true if success, false otherwise (handler gone or muted).
• bool furi_take(FuriRecord record, void* data, size_t size) works as furi_read but lock global mutex. It can be useful if records contain pointer to buffer which you want to change. You must call furi_give after operation on data and you cannot block executing between take and give calls
• bool furi_give(FuriRecord record, const void* data, size_t size) works as furi_wrte but unlock global mutex.
• bool furi_global_take() lock global mutex (as furi_take but without read)
• boold furi_global_give() unlock global mutex ((as furi_give but without write))
• bool furi_unmute(FuriRecord record) unmutes muted record.
• bool furi_mute(FuriRecord record) mutes unmuted record.
• bool furi_subscribe(FuriRecord record, void(cb*)(const void* data, size_t size)) set record change callback.
• bool furi_state_subscribe(FuriRecord record, void(cb*)(bool muted)) set record state change callback (mute/unmute). For example, you can unmute itself after some application open same record, or redraw your application UI when popup application ends.

Usage example

Diagram below describes furi states

• After start, init code run some applications: in this example there is status bar, a background task and Home screen
• Status bar open access to framebuffer by opening "/ui/fb" FURI record
• "Home screen" call "Menu" application by furiac_switch. "Home screen" application stops and then "Menu" application starts.
• "Menu" application call "Your cool app" the same way. It also get access to framebuffer by open "/ui/fb" FURI record
• If "Your cool app" needs some backend app, it call this by furiac_start and then kill by furiac_kill
• If background task needs to show popup message (for example "Low battery") it can call new app or simply open "/ui/fb" record.
• When "/ui/fb" record is opened by popup message, FURI mute framebuffer handle in "Your cool app". This prevent to overwrite popup message by application drawing.
• "Status bar" framebuffer handle also is muted, but it call furi_unmute and unmute itself.
• After popup message is closed by furiac_exit or closing "/ui/fb", FURI unmute previous muted "Your cool app" framebuffer handle.

Status bar also get mute and unmute itself every time when Home screen, Menu or "Your cool app" open framebuffer but diagramm not show it

Data storage

• furi_create_var(char* name) create static-like value handler. You can use all furi_ calls for