Adding Memories and I／O

Memory Block Signals
Address – 32 bits
Mem Write – 1 bit
Write Data – 32 bits
Read Data – 32 bits
Mem Read – 1 bit
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Using 2 Block RAMs
• Illustration from book • Let’s work it out for Block RAMs • Specs next
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Block RAM Specs
Adding Memories and I/O
Anselmo Lastra
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
The MIPS Datapath
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Let’s Add Keyboard Register
• Can put it at location 1024 (binary 100 0000 0000)
• Will now want to decode 3 bits
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Another Approach
• Let’s see how to add a block of x8 character memory for the VGA
• Need to makeRSITY of NORTH CAROLINA at CHAPEL HILL
Memory Map
• Refers to how physical memory is populated
• In our example, memory from 0 to 511
♦ It’s in two blocks, but that’s invisible to programmer
Expanding Memory Block
• First let’s look in detail at data memory block
• See how to add block memories • Add I/O
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Memory Map
0 01 0000 0000 -256
Instruction and Data Memory
Empty
10 0000 0000 512
Character Memory
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In Reality
• Isolated from CPU • On standard buses
♦ PCI
• Ours will be simpler
♦ Just memory addresses
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there
♦ Real computers have flash memory to boot CPU or go to configuration utility
♦ On (very) old computers had to enter boot program on front panel
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• Try 2 256x16
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Adding More Memory
• Illustration from text
• Let’s see how to add 2 more block RAMs to increase mem to 512 words
• What happens if we read location 1025?
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How Does Processor Begin
• One way is to initialize PC to 0 • Make sure to have instructions
Verilog
• Can sketch how to code this in Verilog
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Adding I/O
• Look at memory-mapped I/O • Conceptually like this