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readmemory

Read data out of AXI4 memory-mapped slaves

    Description

    example

    data = readmemory(mem,addr,size) reads size locations of data, starting from the address specified in addr and then incrementing the address for each word. The function casts the data to the uint32 or uint64 data type (depending on the data size of the AXI master IP). The address, addr, must refer to an AXI slave memory location controlled by the AXI master IP on your FPGA board. The aximaster object, mem, manages the connection between MATLAB® and the AXI master IP.

    data = readmemory(mem,addr,size,Name,Value) specifies options using one or more name-value arguments.

    Examples

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    Before you can use this example, you must have a design running on an FPGA board connected to the MATLAB host machine. The FPGA design must include an AXI master IP that is customized for your FPGA vendor. The support package installation includes this IP. To include the IP in your project, see the Access FPGA Memory Using JTAG-Based MATLAB AXI Master example.

    Create an AXI master object. The object connects MATLAB with the FPGA board and confirms that the IP is present.

    mem = aximaster('Xilinx')
    
    mem = 
    
      aximaster with properties:
    
               Vendor: 'Xilinx'
        JTAGCableName: 'auto'
    

    Write 10 addresses and then read data from a single location. By default, these functions auto-increment the address for each word of data.

    writememory(mem,140,[10:19])
    rd_d = readmemory(mem,140,1)
    
    rd_d =
    
      uint32
    
       10
    

    Read data from 10 locations.

    rd_d = readmemory(mem,140,10)
    rd_d =
    
      1×10 uint32 row vector
    
       10   11   12   13   14   15   16   17   18   19
    

    Read data 10 times from the same address by specifying that the AXI master read all data from the same address (disabling auto-incrementation).

    rd_d = readmemory(mem,140,10,'BurstType','Fixed')
    rd_d =
    
      1×10 uint32 row vector
    
       10   10   10   10   10   10   10   10   10   10
    

    Write data 10 times to the same address. In this case, the final value stored in address 140 is 29.

    writememory(mem,140,[20:29],'BurstType','Fixed')
    rd_d = readmemory(mem,140,10)
    rd_d =
    
      1×10 uint32 row vector
    
       29   11   12   13   14   15   16   17   18   19

    Specify the address as a hexadecimal value. Specify for the function to cast the read data to a data type other than uint32.

    writememory(mem,0x1c,[0:4:64])
    rd_d = readmemory(mem,0x1c,16,'OutputDataType',numerictype(0,6,4))
    rd_d = 
    
      Columns 1 through 10
             0    0.2500    0.5000    0.7500    1.0000    1.2500    1.5000    1.7500    2.0000    2.2500
      Columns 11 through 16
        2.5000    2.7500    3.0000    3.2500    3.5000    3.7500
    
              DataTypeMode: Fixed-point: binary point scaling
                Signedness: Unsigned
                WordLength: 6
            FractionLength: 4

    When you no longer need to access the board, release the JTAG connection.

    release(mem)

    Input Arguments

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    Connection to the AXI master IP on your FPGA board, specified as an aximaster object.

    Starting address for the read operation, specified as a nonnegative integer multiple of 4 or hexadecimal value multiple of 4. The function casts the address to the uint32 or uint64 data type, depending on the AXI master IP address width. The address must refer to an AXI slave memory location controlled by the AXI master IP on your FPGA board.

    Memory-Mapping Guidelines

    • If the AXI master IP data width is 32 bits, the memory is 4 bytes aligned, and addresses have 4-byte increments (0x0, 0x4, 0x8). In this case, 0x1 is an illegal address and emits an error.

    • If the AXI master IP data width is 64 bits, the memory is 8 bytes aligned, and addresses have 8-byte increments (0x0, 0x8, 0x10). In this case, 0x1 and 0x4 are illegal and emit errors.

    • If the AXI master IP data width is 32 bits and you set the 'BurstType' argument to 'Increment', the address has 4-byte increments.

    • If the AXI master IP data width is 64 bits and you set the 'BurstType' argument to 'Increment', the address has 8-byte increments.

    • Do not use a 64-bit AXI master for accessing 32-bit registers.

    Example: 0xa4, specifies a starting address of 0xa4.

    Data Types: uint32 | uint64

    Number of memory locations to read, specified as a nonnegative integer. By default, the function reads data from a contiguous address block, incrementing the address for each operation. To disable address incrementation and read repeatedly from the same location, set the 'BurstType' argument to 'Fixed'.

    When you specify a large operation size, such as reading a block of DDR memory, the function automatically breaks the operation into multiple bursts, using the maximum supported burst size of 256 words.

    Example: 5 specifies five contiguous memory locations.

    Name-Value Arguments

    Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

    Example: 'BurstType','Fixed' directs the AXI master to read all data from the same address.

    AXI4 burst type, specified as one of these options:

    • 'Increment' — The AXI master reads a vector of data from contiguous memory locations, starting with the specified address.

    • 'Fixed' — The AXI master reads all data from the same address.

    Data type assigned to the read data, specified as one of these options:

    • 'int8'

    • 'int16'

    • 'int32'

    • 'int64'

    • 'uint8'

    • 'uint16'

    • 'uint32'

    • 'uint64'

    • 'single'

    • 'double'

    • numerictype object

    The function casts the data read out of the FPGA to the specified data type. double is supported for 64-bit UDP connections only.

    Output Arguments

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    Read data, returned as a scalar or vector depending on the value you specify for the size. The function casts the data to the data type specified by the 'OutputDataType' input.

    Introduced in R2017a