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Team Antelope. Progress Report. Antelope Team Progress. Finished: Shifter Register File Multiplier Multiply Accumulate ALU CLZ Still Working On: Cache Instruction Decode Integration. Memory system. Cache Unit. Cache Specs. 16 bytes wide 9 bit line address Write-back
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Team Antelope Progress Report
Antelope Team Progress Finished: Shifter Register File Multiplier Multiply Accumulate ALU CLZ Still Working On: Cache Instruction Decode Integration
Cache Specs • 16 bytes wide • 9 bit line address • Write-back • data + instr caches • Check for dirty blocks in data cache on writes • Clock stalls during main memory interaction
32-Bit Barrel Shifter Carry In / Carry Out -Carry in only used in RRX (rotate right extended) operations -Carry out always computed, even though not needed in rotate operations
Carry Out Logic: Two Options • Separate logic computes Cout early using input and shift amount Pros: -Cout signal ready much earlier, no need for propagation -Simpler bit shifter designs Cons: -Many more gates needed
Carry Out Logic: Two Options • Individual bit shifters compute and propagate Cout signal Pros: -Simpler overall design -Fewer logic gates Cons: -Takes longer for Cout to be ready (propagation delay) -More complicated bit shifters
Conclusion • Went ahead and implemented Cout logic in the bit shifters -Don’t really need the signal to be ready any earlier than the rest of the shifter output, especially not at the addition gate cost -Each shifter computes Cout for its own shift amount and passes it on, or leaves Cout alone if it is disabled
Barrel Shifter Added 32-bit Shifters Result propagated through bit shifters
Multiplier (MUL/MLA) • 32 additions in parallel • Logarithmic time result • 25 = 32, so time equals 5 adds • Multiply w/accumulate inserted at the end with a multiplexor
Count leading zeros (CLZ) • Output equals number of leading zeros on the input (Ex: 00010110 00000011) • First step: 00010110 00011111 • Then, add one: 00011111 00100000 • Lastly, convert to binary. With a 32-bit input, output will have a 6-digit maximum.
CLZ Timing • Time equals: • 2x 16-bit OR gate • 1x 2-bit OR gate • 1x 2-bit XOR gate • Perhaps faster than an addition!
Register File Complete • 37 total registers • 4 outputs Register1 out, Register2 out, CPSR out, and PC out • 7 inputs: ReadSelect1, ReadSelect2, Mode, WriteEnable, Clk, PC, CPSR
Integration Status • Most components are complete • Ready to start running most instructions • Need to make stage buffers • Most importantly, need to start figuring out the control structure