espressif/esp_modem

uploaded 2 years ago

# ESP MODEM This component is used to communicate with modems in command and data modes. It abstracts the UART I/O processing into a DTE (data terminal equipment) entity which is configured and setup separately. On top of the DTE, the command and data processing is performed in a DCE (data communication equipment) unit. ``` esp-modem - start-ppp +-------+ +-------+ - stop-ppp | reset | | retry | - events | helper| | helper| +-------+ +-------+ +-----+ +-----+ . . | DTE |--+->| DCE |....................... +-----+ | +-----+ | | +-------------+ +-----+ +->| modem-netif | | PPP |------->| | +-----+ +-------------+ ``` ## Start-up sequence To initialize the modem we typically: * create DTE with desired UART parameters * create DCE with desired command palette and attach it to the DTE * create PPP netif and attach it to the DTE * configure event handlers for the modem and the netif Then we can start and stop PPP mode using esp-modem API, as well as receive events from the `ESP_MODEM` base as well as from netif (IP events). ### DTE Responsibilities of the DTE unit are * sending/receiving commands to/from UART * sending/receiving data to/from UART * changing data/command mode on physical layer ### DCE Responsibilities of the DCE unit are * definition of available commands * cooperate with DTE on changing data/command mode ### PPP-netif The modem-netif attaches the network interface (which was created outside of esp-modem) to the DTE and serves as a glue layer between esp-netif and esp-modem. ### Additional units ESP-MODEM provides these two modules, that could be used in addition to with other units to make modem communication more robust: * reset-helper is a very simple GPIO pulse generator, which could be typically used to reset or power up/down the module * retry-strategy is a command executor abstraction, that helps with retrying sending commands in case of a failure or a timeout. ## Modification of existing DCE In order to support an arbitrary modem, device or introduce a new command we typically have to either modify the DCE, adding a new or altering an existing command or creating a new "subclass" of the existing DCE variants. ## Internal design