def get_data_dev(sector):
drive.seek((2000+sector)*512)
data = drive.read(512)
if len(data) != 512:
data = ''
return data
read_crc = struct.unpack('H', data[-2:])[0]
calc_crc = shimmerUtil.crc_compute(data[0:-2])
if read_crc != calc_crc:
data = ''
return data
def get_data_port(sector):
"""
Reads a sector off of the SHIMMER sd card.
This function returns the 512 bytes read from sd card on the
sector specified. Sector 0 is the file header, and the data is on
the following sectors. If there was a problem reading from the sd
card, the empty string is returned.
"""
data = ''
marker_not_found = 1
# Command to read sector
ser.write('f' + struct.pack('I', sector))
# Look for start marker
markers_seen = 0
marker_found = 0
while not marker_found:
char = ser.read(1)
# check for timeout
if char == '':
return data
if char == '\xaa':
markers_seen += 1
if markers_seen == 4:
marker_found = 1
else:
markers_seen = 0
# Found start of sector
data = ser.read(512)
if len(data) != 512:
data = ''
return data
read_crc = struct.unpack('H', data[-2:])[0]
calc_crc = shimmerUtil.crc_compute(data[0:-2])
if read_crc != calc_crc:
data = ''
return data
new_offset = struct.unpack('d',offset_str)[0]
if new_offset != offset:
print "Error writing offset to SHIMMER. Please try again."
ser.close()
sys.exit(1)
# We are now ready to generate our marker block. The marker starts
# with the 0x0000 (normally the SHIMMER timestamp goes here) and then
# the 8 byte offset offset followed by 500 bytes of random characters
# and a 2 byte checksum.
data = '\x00\x00' + offset_str
for i in range(500):
data += chr(random.randint(0,255))
data += struct.pack('H',shimmerUtil.crc_compute(data))
# Now send this marker to SHIMMER
# We have the offset. Now store it on the SHIMMER
ser.write('m')
ser.write(data)
ser.write('e')
new_data = ser.read(512)
if new_data != data:
print "File marker mismatch. Please try again."
ser.close()
sys.exit(1)
now = time.strftime('%m/%d/%Y %H:%M:%S',
