def read_idcodes(self):
"""return a tuple of idcodes for the JTAG chain"""
# a TAP reset leaves the idcodes in the DR chain
self.driver.tap_reset()
tdi = bits.ones(self.n * _idcode_length)
tdo = bits.null()
self.driver.scan_dr(tdi, tdo)
return tdo.split((_idcode_length, ) * self.n)
def rw_dr(self, wr):
"""read/write DR for a device"""
tdi = bits.ones(self.devs_before).tail(wr).tail1(self.devs_after)
tdo = bits.null()
self.chain.driver.scan_dr(tdi, tdo)
# strip the dr bits from the bypassed devices
tdo.drop_head(self.devs_before)
tdo.drop_tail(self.devs_after)
return tdo
def rw_ir(self, wr):
"""read/write IR for a device"""
tdi = bits.ones(self.irlen_before).tail(wr).tail1(self.irlen_after)
tdo = bits.null()
self.chain.driver.scan_ir(tdi, tdo)
# strip the ir bits from the other devices
tdo.drop_head(self.irlen_before)
tdo.drop_tail(self.irlen_after)
return tdo
def chain_length(self, scan):
"""return the length of the JTAG chain"""
tdo = bits.null()
# build a 000...001000...000 flush buffer for tdi
tdi = bits.zeroes(_flush_size).tail1(1).tail0(_flush_size)
scan(tdi, tdo)
# the first bits are junk
tdo.drop_head(_flush_size)
# work out how many bits tdo is behind tdi
s = tdo.bit_str()
s = s.lstrip('0')
if len(s.replace('0', '')) != 1:
raise Error, 'unexpected result from jtag chain, there should be a single 1'
return len(s) - 1
def test1(self):
x = bits.null()
self.assertEqual(str(x), '(0) ')