Reading Address 3 of a 2×2 memory

Reading Address 3 from a 2x2 memory refers to accessing the third element in a two-dimensional array where each row has exactly two elements. In a 2x2 matrix representation, we typically have four cells arranged like this:

[0, 1]
[2, 3]

Addressing starts with the top-left corner as 0 (row 0, column 0), followed by the top-right (row 0, column 1), then the bottom-left (row 1, column 0), and finally the bottom-right (row 1, column 1). So, if you want to read the value at address 3, which is the third element, it corresponds to the element located at position (1, 1) or [2] in the numerical indexing system, because counting starts from 0.

相关问题

Write a program to 1.Setup a simulating backing store in memory. Read the data from pdata.bin to this backing store. 2.Initialize a page table for process p, set the frame number to be -1 for each page, indicating that the page is not loaded into memory yet. 3.Read logical addresses one by one from la.txt. 4.For each logical address, a)if its page has been loaded into physical memory, simply find the frame number in the page table, then generate physical address, find and print out the physical address and data inside this address. b)if the page is used for the first time, i.e., in page table, its frame number is -1，then the page that contains this address should be loaded into a free frame in physical memory (RAM). Then update the page table by adding the frame number to the right index in the page table. Then repeat 4a). Assumption: 1.Assume the file la.txt includes the sequence of generated addresses from CPU. 2.Use a part of memory as backing store that store data for a process. 3.The backing store size is 128 bytes 4.The size of process p is 128 bytes. 5.The contents of p is included in a file pdata.bin which is a binary file. 6.Use a part of memory as RAM. The size of physical memory is 256 bytes, from 0 to 255. All the physical memory is available, allocating starting from beginning in sequence. That is, allocate frame 0 first, then frame 1, then frame 2…. 7.The size of a frame is 32 bytes, i.e., 5 bits for the offset in a frame, total number of frames is 8. At beginning, no page table is available for process p.

Here is a sample program that implements the steps you described:

BACKING_STORE_SIZE = 128
PHYSICAL_MEMORY_SIZE = 256
PAGE_SIZE = 32
NUM_FRAMES = PHYSICAL_MEMORY_SIZE // PAGE_SIZE

# Initialize backing store
backing_store = bytearray(BACKING_STORE_SIZE)
with open("pdata.bin", "rb") as f:
    pdata = f.read()
    backing_store[:len(pdata)] = pdata

# Initialize page table
page_table = [-1] * (BACKING_STORE_SIZE // PAGE_SIZE)

# Initialize physical memory
physical_memory = [bytearray(PAGE_SIZE) for _ in range(NUM_FRAMES)]

# Read logical addresses from la.txt
with open("la.txt", "r") as f:
    for line in f:
        logical_address = int(line.strip())
        page_number = logical_address // PAGE_SIZE
        offset = logical_address % PAGE_SIZE

        # Check if page is already in physical memory
        frame_number = page_table[page_number]
        if frame_number != -1:
            physical_address = frame_number * PAGE_SIZE + offset
            data = physical_memory[frame_number][offset]
            print("Physical address:", physical_address, "Data:", data)

        # If page is not in physical memory, load it
        else:
            # Find a free frame in physical memory
            frame_number = None
            for i in range(NUM_FRAMES):
                if page_table.count(i) == 0:
                    frame_number = i
                    break

            if frame_number is None:
                print("Error: no free frame available in physical memory")
                break

            # Load page from backing store to physical memory
            page_start = page_number * PAGE_SIZE
            page_data = backing_store[page_start:page_start + PAGE_SIZE]
            physical_memory[frame_number][:] = page_data

            # Update page table
            page_table[page_number] = frame_number

            # Print physical address and data
            physical_address = frame_number * PAGE_SIZE + offset
            data = physical_memory[frame_number][offset]
            print("Physical address:", physical_address, "Data:", data)

Here is an overview of how the program works:

1. The program initializes the backing store by reading the contents of `pdata.bin` into a byte array. It also initializes the page table with -1 values, indicating that no pages are loaded into physical memory yet.

2. The program creates a byte array for each frame in physical memory, and initializes them all to 0.

3. The program reads logical addresses from `la.txt` one by one.

4. For each logical address, the program computes the page number and offset.

5. If the page is already loaded into physical memory (i.e., its frame number is not -1), the program computes the physical address and reads the data from the corresponding byte array in physical memory.

6. If the page is not yet loaded into physical memory, the program searches for a free frame, loads the page from the backing store to the frame, updates the page table with the frame number, and then reads the data from the corresponding byte array in physical memory.

7. The program prints the physical address and data for each logical address.

Note that this program assumes that there is always at least one free frame in physical memory. If there are no free frames, the program will print an error message and stop.

i2c repeat start

I2C repeat start is a signal that initiates a new transmission on the I2C bus without releasing the bus. It is used to send multiple data bytes to the same slave device without the need to readdress the device.

The I2C repeat start condition is generated by the master device after sending a data byte to the slave device. Instead of sending a stop condition to release the bus, the master sends a start condition followed by the slave address and the R/W bit. This tells the slave device that the master wishes to continue the communication and there is no need to release the bus.

Repeat start is useful in situations where multiple data bytes need to be sent to the same slave device, such as when reading or writing a large amount of data from a sensor or memory device. It saves time and reduces the overhead of address and control byte transmission.

It is important to note that not all I2C devices support the repeat start condition. It is recommended to check the device datasheet to confirm if it is supported.