Single-Chip Flash Device with Boot Code Transfer Capability

摘要

A Multi-Media Card (MMC) Single-Chip Flash Device (SCFD) contains a MMC flash microcontroller and flash mass storage blocks containing flash memory arrays that are block-addressable rather than randomly-addressable. An initial boot loader is read from the first page of flash by a state machine and written to a small RAM. A central processing unit (CPU) in the microcontroller reads instructions from the small RAM, executing the initial boot loader, which reads more pages from flash. These pages are buffered by the small RAM and written to a larger DRAM. Once an extended boot sequence is written to DRAM, the CPU toggles a RAM_BASE bit to cause instruction fetching from DRAM. Then the extended boot sequence is executed from DRAM, copying an OS image from flash to DRAM. Boot code and control code are selectively overwritten during a code updating operation to eliminate stocking issues.