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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 Demonstrate interleaving source arrays using DMA scatter/gather.
Each source array gets a corresponding Transfer Control Descriptor (TCD) containing
Step1:  Simulate concatenate behaviour on host (i.e., using numpy)
Step2:  Device
Connect to device
Step3:  Allocate arrays
Source array (input chunks)
Destination array (space for concatenated result)
Array of Transfer Control Descriptor (TCD) structures (one TCD per chunk)
Step4:  Create Transfer Control Descriptor (TCD) configurations
Step5:  Load first TCD in scatter chain and enable scatter/gather
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Python Code:
import numpy as np
# Configurable test settings
channel_count = 3  # Simulate sampling from multiple channels.
sample_count = 8  # Number of samples (each sample -> one value per channel).
N = channel_count * sample_count
src_data = np.arange(1, N + 1, dtype='uint8')
Explanation: Demonstrate interleaving source arrays using DMA scatter/gather.
Each source array gets a corresponding Transfer Control Descriptor (TCD) containing:
Destination address in output array to write to.
Stride set through DOFF field to achieve interleaved writing pattern.
DLASTSGA field set to the address of the next TCD in memory (except for last TCD,
   which points back to first TCD).
Host
Define size and number of chunks
End of explanation
src_chunks = [src_data[i * channel_count:(i + 1) * channel_count]
              for i in xrange(sample_count)]
dst_data = np.column_stack(src_chunks).ravel()
for i, chunk in enumerate(src_chunks):
    print 'SOURCE%d:' % i, chunk
# Show interleaved result
print 'TARGET:', dst_data
Explanation: Simulate concatenate behaviour on host (i.e., using numpy)
End of explanation
from teensy_minimal_rpc import SerialProxy
import teensy_minimal_rpc.DMA as dma
# Disconnect from existing proxy (if available)
try:
    del proxy
except NameError:
    pass
proxy = SerialProxy()
Explanation: Device
Connect to device
End of explanation
proxy.free_all()
# Allocate source array
src_addr = proxy.mem_alloc(N)
# Allocate destination array
dst_addr = proxy.mem_alloc(N)
src_addrs = [src_addr + i * channel_count for i in xrange(sample_count)]
tcds_addr = proxy.mem_aligned_alloc(32, sample_count * 32)
hw_tcds_addr = 0x40009000
tcd_addrs = [tcds_addr + 32 * i for i in xrange(sample_count)]
hw_tcd_addrs = [hw_tcds_addr + 32 * i for i in xrange(sample_count)]
# Fill first 16 bytes of source array with the numbers 1-N
proxy.mem_cpy_host_to_device(src_addr, src_data)
for i in xrange(sample_count):
    print 'SOURCE%d:  ' % i, proxy.mem_cpy_device_to_host(src_addrs[i], channel_count)
Explanation: Allocate arrays
Source array (input chunks)
Destination array (space for concatenated result)
Array of Transfer Control Descriptor (TCD) structures (one TCD per chunk)
End of explanation
# Create Transfer Control Descriptor configuration for first chunk, encoded
# as a Protocol Buffer message.
tcd0_msg = dma.TCD(CITER_ELINKNO=dma.R_TCD_ITER_ELINKNO(ITER=1),
                   BITER_ELINKNO=dma.R_TCD_ITER_ELINKNO(ITER=1),
                   ATTR=dma.R_TCD_ATTR(SSIZE=dma.R_TCD_ATTR._8_BIT,
                                       DSIZE=dma.R_TCD_ATTR._8_BIT),
                   NBYTES_MLNO=channel_count,
                   SADDR=int(src_addrs[0]),
                   SOFF=1,
                   SLAST=-channel_count,
                   DADDR=int(dst_addr),
                   DOFF=sample_count,
                   DLASTSGA=int(tcd_addrs[1]),
                   CSR=dma.R_TCD_CSR(START=0, DONE=False, ESG=True))
# Convert Protocol Buffer encoded TCD to bytes structure.
tcd0 = proxy.tcd_msg_to_struct(tcd0_msg)
# Create binary TCD struct for each TCD protobuf message and copy to device
# memory.
for i, src_addr_i in enumerate(src_addrs):
    tcd_i = tcd0.copy()
    tcd_i['SADDR'] = src_addr_i
    tcd_i['DADDR'] = dst_addr + i
    tcd_i['DLASTSGA'] = tcd_addrs[(i + 1) % len(tcd_addrs)]
    tcd_i['CSR'] |= (1 << 4)  # | 0x1  # Automatically start transfers 2-n
    # __N.B.,__ Setting `START` bit causes destination bus error.
#     if i > 0:
#         tcd_i['CSR'] |= 0x1  # Automatically start transfers 2-n
    proxy.mem_cpy_host_to_device(tcd_addrs[i], tcd_i.tostring())
Explanation: Create Transfer Control Descriptor (TCD) configurations
End of explanation
# Fill the destination array with all zeros (to show transfer progress below).
proxy.mem_fill_uint32(dst_addr, 0, N / 4)
for i in xrange(sample_count):
    print 'SOURCE%d:  ' % i, proxy.mem_cpy_device_to_host(src_addrs[i], channel_count)
# Load initial TCD to DMA channel 0.
proxy.mem_cpy_host_to_device(hw_tcd_addrs[0], tcd0.tostring())
print 'DEST:'
# Trigger once per chunk
for i in xrange(sample_count):
    proxy.update_dma_registers(dma.Registers(SSRT=0))
    device_dst_data = proxy.mem_cpy_device_to_host(dst_addr, N)
    print '   Trigger %d:' % i, device_dst_data
    
# Verify device result matches expected result computed on host.
assert((device_dst_data == dst_data).all())
Explanation: Load first TCD in scatter chain and enable scatter/gather
End of explanation
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