MMC module communicates with the external data storage - MultiMediaCard. It enables to write content of blocks from MMC to SRAM and back, and also controls the access to virtual disks on MMC.
This module communicates with MMC card via SPI interface of node 705. It provides elementary access words to nodes 703 and 706, which can write and read, respectively, whole blocks to/from MMC. The two nodes access SRAM module via ether messages sent to node 107.
Node 704 contains code that switches GPIO 600.17 (CS signal) high, thus disabling onboard SPI flash memory and enabling MMC. Next, it initializes MMC card into SPI mode. After initialization, this node functions as a wire allowing communication of nodes 703 and 705, i.e. when we wish to write SRAM content to MMC.
Upon boot up, when all system nodes have been loaded, node 707 sends a signal to node 308, which effectively starts Editor in command mode. This is indicated by cursor appearance at the beginning of the bottom screen row. This node also receives requests from Interpreter to change virtual disk, and passes this request to nodes 703 and 706. Virtual disks are explained in Mass storage chapter of system description.
Node 705 is the last one loaded either from the onboard SPI flash memory (standalone version) or from PC via async serial line (umbilical version). When loaded, it sends signal to node 704 to set CS signal high, and to node 707 to start the system.