devmem

devmem is a command in BusyBox. It can read from and write to hardware registers by using the mmap function to map device memory into user space via the mmap method of the /dev/mem driver, thereby enabling read/write operations on physical addresses.

Syntax

devmem ADDRESS [WIDTH [VALUE]]
  
  Read/write from physical address

        ADDRESS Address to act upon
        WIDTH   Width (8/16/...)
        VALUE   Data to be written

• ADDRESS: The physical address on which to perform the operation. This is a required parameter specifying the address to read from or write to.
• WIDTH: An optional parameter indicating the data width. It can be specified as 8, 16, or 32, defining the bit-width of the data to read or write. If omitted, it defaults to 32 bits.
• VALUE: An optional parameter representing the data value to write. If WIDTH is provided, VALUE must match the specified width. If VALUE is omitted, the command performs a read operation.

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Common Commands

• Reading registers

Read 32-bit: devmem 0xa600307c 32
Read 16-bit: devmem 0xa600307c 16
Read 8-bit:  devmem 0xa600307c 8

• Writing registers

Write 32-bit: devmem 0xa6003078 32 0x1000100
Write 16-bit: devmem 0xa6003078 16 0x1234
Write 8-bit:  devmem 0xa6003078 8 0x12