Vol. 1 12-13

PROGRAMMING WITH INTEL® SSE3, SSSE3, INTEL® SSE4 AND INTEL® AESNI

Example 12-1.  Sketch of MOVNTDQA Usage of a Consumer and a PCI Producer 

// P0: producer is a PCI device writing into the WC space
# the PCI device updates status through a UC flag, "u_dev_status" . 
# the protocol for "u_dev_status" : 0: produce; 1: consume; 2: all done

mov eax, $0
mov [u_dev_status], eax

producerStart:

mov eax, [u_dev_status]     # poll status flag to see if consumer is requestion data
cmp eax, $0                           # 
jne done                                # I no longer need to produce                       
commence PCI writes to WC region..

mov eax, $1  # producer ready to notify the consumer via status flag
mov  [u_dev_status], eax     

# now wait for consumer to signal its status
spinloop:

cmp [u_dev_status], $1      # did I get a signal from the consumer ?
jne producerStart                  # yes I did 
jmp spinloop                         # check again

done:
// producer is finished at this point 

// P1: consumer check PCI status flag to consume WC data

mov eax, $0  # request to the producer 
mov [u_dev_status], eax

consumerStart:

mov; eax, [u_dev_status]  # reads the value of the PCI status 
cmp eax, $1                                 # has producer written
jne consumerStart                       # tight loop; make it more efficient with pause, etc. 
mfence # producer finished device writes to WC, ensure WC region is coherent

ntread:

movntdqa xmm0, [addr]
movntdqa xmm1, [addr + 16]
movntdqa xmm2, [addr + 32]
movntdqa xmm3, [addr + 48]
…  # do any more NT reads as needed
mfence  # ensure PCI device reads the correct value of [u_dev_status]  

# now decide whether we are done or we need the producer to produce more data
# if we are done write a 2 into the variable, otherwise write a 0 into the variable

mov eax, $0/$2            # end or continue producing
mov [u_dev_status], eax

# if I want to consume again I will jump back to consumerStart after storing a 0 into eax
# otherwise I am done