From: Gerhard Sittig Date: Sat, 12 Nov 2016 22:19:47 +0000 (+0100) Subject: avr_pdi: introduce decoder for Atmel Program and Debug Interface X-Git-Tag: libsigrokdecode-0.5.0~97 X-Git-Url: https://sigrok.org/gitweb/?p=libsigrokdecode.git;a=commitdiff_plain;h=f0349f7f5bae7cff479772fa9791d3f7f311dfc3 avr_pdi: introduce decoder for Atmel Program and Debug Interface Introduce a decoder for Atmel's proprietary programming and debugging interface which got introduced with ATxmega chips. This implementation supports the UART style physical (two wires PDI_CLK and PDI_DATA). --- diff --git a/decoders/avr_pdi/__init__.py b/decoders/avr_pdi/__init__.py new file mode 100644 index 0000000..ebe647b --- /dev/null +++ b/decoders/avr_pdi/__init__.py @@ -0,0 +1,41 @@ +## +## This file is part of the libsigrokdecode project. +## +## Copyright (C) 2016 Gerhard Sittig +## +## This program is free software; you can redistribute it and/or modify +## it under the terms of the GNU General Public License as published by +## the Free Software Foundation; either version 2 of the License, or +## (at your option) any later version. +## +## This program is distributed in the hope that it will be useful, +## but WITHOUT ANY WARRANTY; without even the implied warranty of +## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +## GNU General Public License for more details. +## +## You should have received a copy of the GNU General Public License +## along with this program; if not, see . +## + +''' +PDI (Program and Debug Interface) is an Atmel proprietary interface for +external programming and on-chip debugging of the device. See the Atmel +Application Note AVR1612 "PDI programming driver" and the "Program and +Debug Interface" section in the Xmega A manual for details. + +The protocol uses two pins: the RESET pin and one dedicated DATA pin. +The RESET pin provides a clock, the DATA pin communicates serial frames +with a start bit, eight data bits, an even parity bit, and two stop bits. +Data communication is bidirectional and half duplex, the device will +provide response data after reception of a respective request. + +Protocol frames communicate opcodes and their arguments, which provides +random and sequential access to the device's address space. By accessing +the registers of internal peripherals, especially the NVM controller, +it's possible to identify the device, read from and write to several +kinds of memory (signature rows, fuses and lock bits, internal flash and +EEPROM, memory mapped peripherals), and to control execution of software +on the device. +''' + +from .pd import Decoder diff --git a/decoders/avr_pdi/pd.py b/decoders/avr_pdi/pd.py new file mode 100644 index 0000000..1568fdf --- /dev/null +++ b/decoders/avr_pdi/pd.py @@ -0,0 +1,586 @@ +## +## This file is part of the libsigrokdecode project. +## +## Copyright (C) 2011-2014 Uwe Hermann +## Copyright (C) 2016 Gerhard Sittig +## +## This program is free software; you can redistribute it and/or modify +## it under the terms of the GNU General Public License as published by +## the Free Software Foundation; either version 2 of the License, or +## (at your option) any later version. +## +## This program is distributed in the hope that it will be useful, +## but WITHOUT ANY WARRANTY; without even the implied warranty of +## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +## GNU General Public License for more details. +## +## You should have received a copy of the GNU General Public License +## along with this program; if not, see . +## + +# Note the implementation details: +# +# Although the Atmel literature suggests (does not explicitly mandate, +# but shows in diagrams) that two stop bits are used in the protocol, +# the decoder loses synchronization with ATxmega generated responses +# when it expects more than one stop bit. Since the chip's hardware is +# fixed, this is not an implementation error in some programmer software. +# Since this is a protocol decoder which does not participate in the +# communication (does not actively send data), we can read the data +# stream with one stop bit, and transparently keep working when two +# are used. +# +# Annotations in the UART fields level differ from Atmel literature. +# Wrong parity bits are referred to as "parity error". Low stop bits are +# referred to as "frame error". +# +# The PDI component in the device starts disabled. Enabling PDI +# communication is done by raising DATA and clocking RESET with a +# minimum frequency. PDI communication automatically gets disabled when +# RESET "is inactive" for a certain period of time. The specific timing +# conditions are rather fuzzy in the literature (phrased weakly), and +# are device dependent (refer to the minumum RESET pulse width). This +# protocol decoder implementation internally prepares for but currently +# does not support these enable and disable phases. On the one hand it +# avoids excess external dependencies or wrong results for legal input +# data. On the other hand the decoder works when input streams start in +# the middle of an established connection. +# +# Communication peers detect physical collisions. The decoder can't. +# Upon collisions, a peer will cease any subsequent transmission, until +# a BREAK is seen. Synchronization can get enforced by sending two BREAK +# conditions. The first will cause a collision, the second will re-enable +# the peer. The decoder has no concept of physical collisions. It stops +# the interpretation of instructions when BREAK is seen, and assumes +# that a new instruction will start after BREAK. +# +# This protocol decoder only supports PDI communication over UART frames. +# It lacks support for PDI over JTAG. This would require separation into +# multiple protocol decoder layers (UART physical, JTAG physical, PDI +# instructions, optionally device support on top of PDI. There is some +# more potential for future extensions: +# - The JTAG physical has dedicated TX and RX directions. This decoder +# only picks up communicated bytes but does not check which "line" +# they are communicated on (not applicable to half duplex UART). +# - PDI over JTAG uses "special frame error" conditions to communicate +# additional symbols: BREAK (0xBB with parity 1), DELAY (0xDB with +# parity 1), and EMPTY (0xEB with parity 1). +# - Another "device support" layer might interpret device specific +# timings, and might map addresses used in memory access operations +# to component names, or even register names and bit fields(?). It's +# quite deep a rabbithole though... + +import sigrokdecode as srd +from collections import namedtuple + +class Ann: + '''Annotation and binary output classes.''' + ( + BIT, START, DATA, PARITY_OK, PARITY_ERR, + STOP_OK, STOP_ERR, BREAK, + OPCODE, DATA_PROG, DATA_DEV, PDI_BREAK, + ENABLE, DISABLE, COMMAND, + ) = range(15) + ( + BIN_BYTES, + ) = range(1) + +Bit = namedtuple('Bit', 'val ss es') + +class PDI: + '''PDI protocol instruction opcodes, and operand formats.''' + ( + OP_LDS, OP_LD, OP_STS, OP_ST, + OP_LDCS, OP_REPEAT, OP_STCS, OP_KEY, + ) = range(8) + pointer_format_nice = [ + '*(ptr)', + '*(ptr++)', + 'ptr', + 'ptr++ (rsv)', + ] + pointer_format_terse = [ + '*p', + '*p++', + 'p', + '(rsv)', + ] + ctrl_reg_name = { + 0: 'status', + 1: 'reset', + 2: 'ctrl', + } + +class Decoder(srd.Decoder): + api_version = 2 + id = 'avr_pdi' + name = 'AVR PDI' + longname = 'Atmel Program and Debug Interface' + desc = 'Atmel proprietary interface for the ATxmega MCU.' + license = 'gplv2+' + inputs = ['logic'] + outputs = ['pdi'] + channels = ( + {'id': 'reset', 'name': 'RESET', 'desc': 'RESET / PDI_CLK'}, + {'id': 'data', 'name': 'DATA', 'desc': 'PDI_DATA'}, + ) + annotations = ( + ('uart-bit', 'UART bit'), + ('start-bit', 'Start bit'), + ('data-bit', 'Data bit'), + ('parity-ok', 'Parity OK bit'), + ('parity-err', 'Parity error bit'), + ('stop-ok', 'Stop OK bit'), + ('stop-err', 'Stop error bit'), + ('break', 'BREAK condition'), + ('opcode', 'Instruction opcode'), + ('data-prog', 'Programmer data'), + ('data-dev', 'Device data'), + ('pdi-break', 'BREAK at PDI level'), + ('enable', 'Enable PDI'), + ('disable', 'Disable PDI'), + ('cmd-data', 'PDI command with data'), + ) + annotation_rows = ( + ('uart_bits', 'UART bits', (Ann.BIT,)), + ('uart_fields', 'UART fields', (Ann.START, Ann.DATA, Ann.PARITY_OK, + Ann.PARITY_ERR, Ann.STOP_OK, Ann.STOP_ERR, Ann.BREAK)), + ('pdi_fields', 'PDI fields', (Ann.OPCODE, Ann.DATA_PROG, Ann.DATA_DEV, + Ann.PDI_BREAK)), + ('pdi_cmds', 'PDI Cmds', (Ann.ENABLE, Ann.DISABLE, Ann.COMMAND)), + ) + binary = ( + ('bytes', 'PDI protocol bytes'), + ) + + def __init__(self): + self.samplerate = None + # Detect input changes and clock edges. + self.prev_pins = None + self.prev_clock = None + self.clear_state() + + def clear_state(self): + # Track bit times and bit values. + self.ss_last_fall = None + self.data_sample = None + self.ss_curr_fall = None + # Collect UART frame bits into byte values. + self.bits = [] + self.zero_count = 0 + self.zero_ss = None + self.break_ss = None + self.break_es = None + self.clear_insn() + + def clear_insn(self): + # Collect instructions and their arguments, + # properties of the current instructions. + self.insn_rep_count = 0 + self.insn_opcode = None + self.insn_wr_counts = [] + self.insn_rd_counts = [] + # Accumulation of data items as bytes pass by. + self.insn_dat_bytes = [] + self.insn_dat_count = 0 + self.insn_ss_data = None + # Next layer "commands", instructions plus operands. + self.cmd_ss = None + self.cmd_insn_parts_nice = [] + self.cmd_insn_parts_terse = [] + + def metadata(self, key, value): + if key == srd.SRD_CONF_SAMPLERATE: + self.samplerate = value + + def start(self): + self.out_ann = self.register(srd.OUTPUT_ANN) + self.out_binary = self.register(srd.OUTPUT_BINARY) + + def put_ann_bit(self, bit_nr, ann_idx): + b = self.bits[bit_nr] + self.put(b.ss, b.es, self.out_ann, [ann_idx, [str(b.val)]]) + + def put_ann_data(self, bit_nr, ann_data): + b = self.bits[bit_nr] + self.put(b.ss, b.es, self.out_ann, ann_data) + + def put_ann_row_val(self, ss, es, row, value): + self.put(ss, es, self.out_ann, [row, value]) + + def put_bin_bytes(self, ss, es, row, value): + self.put(ss, es, self.out_binary, [row, value]) + + def handle_byte(self, ss, es, byteval): + '''Handle a byte at the PDI protocol layer.''' + + # Handle BREAK conditions, which will abort any + # potentially currently executing instruction. + is_break = byteval is None + if is_break: + self.cmd_insn_parts_nice.append('BREAK') + self.cmd_insn_parts_terse.append('BRK') + self.insn_rep_count = 0 + # Will FALLTHROUGH to "end of instruction" below. + + # Decode instruction opcodes and argument sizes + # from the first byte of a transaction. + if self.insn_opcode is None and not is_break: + opcode = (byteval & 0xe0) >> 5 + arg30 = byteval & 0x0f + arg32 = (byteval & 0x0c) >> 2 + arg10 = byteval & 0x03 + self.insn_opcode = opcode + self.cmd_ss = ss + mnemonics = None + if opcode == PDI.OP_LDS: + # LDS: load data, direct addressing. + # Writes an address, reads a data item. + width_addr = arg32 + 1 + width_data = arg10 + 1 + self.insn_wr_counts = [width_addr] + self.insn_rd_counts = [width_data] + mnemonics = [ + 'Insn: LDS a{:d}, m{:d}'.format(width_addr, width_data), + 'LDS a{:d}, m{:d}'.format(width_addr, width_data), 'LDS', + ] + self.cmd_insn_parts_nice = ['LDS'] + self.cmd_insn_parts_terse = ['LDS'] + elif opcode == PDI.OP_LD: + # LD: load data, indirect addressing. + # Reads a data item, with optional repeat. + ptr_txt = PDI.pointer_format_nice[arg32] + ptr_txt_terse = PDI.pointer_format_terse[arg32] + width_data = arg10 + 1 + self.insn_wr_counts = [] + self.insn_rd_counts = [width_data] + if self.insn_rep_count: + self.insn_rd_counts.extend(self.insn_rep_count * [width_data]) + self.insn_rep_count = 0 + mnemonics = [ + 'Insn: LD {:s} m{:d}'.format(ptr_txt, width_data), + 'LD {:s} m{:d}'.format(ptr_txt, width_data), 'LD', + ] + self.cmd_insn_parts_nice = ['LD', ptr_txt] + self.cmd_insn_parts_terse = ['LD', ptr_txt_terse] + elif opcode == PDI.OP_STS: + # STS: store data, direct addressing. + # Writes an address, writes a data item. + width_addr = arg32 + 1 + width_data = arg10 + 1 + self.insn_wr_counts = [width_addr, width_data] + self.insn_rd_counts = [] + mnemonics = [ + 'Insn: STS a{:d}, i{:d}'.format(width_addr, width_data), + 'STS a{:d}, i{:d}'.format(width_addr, width_data), 'STS', + ] + self.cmd_insn_parts_nice = ['STS'] + self.cmd_insn_parts_terse = ['STS'] + elif opcode == PDI.OP_ST: + # ST: store data, indirect addressing. + # Writes a data item, with optional repeat. + ptr_txt = PDI.pointer_format_nice[arg32] + ptr_txt_terse = PDI.pointer_format_terse[arg32] + width_data = arg10 + 1 + self.insn_wr_counts = [width_data] + self.insn_rd_counts = [] + if self.insn_rep_count: + self.insn_wr_counts.extend(self.insn_rep_count * [width_data]) + self.insn_rep_count = 0 + mnemonics = [ + 'Insn: ST {:s} i{:d}'.format(ptr_txt, width_data), + 'ST {:s} i{:d}'.format(ptr_txt, width_data), 'ST', + ] + self.cmd_insn_parts_nice = ['ST', ptr_txt] + self.cmd_insn_parts_terse = ['ST', ptr_txt_terse] + elif opcode == PDI.OP_LDCS: + # LDCS: load control/status. + # Loads exactly one byte. + reg_num = arg30 + reg_txt = PDI.ctrl_reg_name.get(reg_num, 'r{:d}'.format(reg_num)) + reg_txt_terse = '{:d}'.format(reg_num) + self.insn_wr_counts = [] + self.insn_rd_counts = [1] + mnemonics = [ + 'Insn: LDCS {:s}, m1'.format(reg_txt), + 'LDCS {:s}, m1'.format(reg_txt), 'LDCS', + ] + self.cmd_insn_parts_nice = ['LDCS', reg_txt] + self.cmd_insn_parts_terse = ['LDCS', reg_txt_terse] + elif opcode == PDI.OP_STCS: + # STCS: store control/status. + # Writes exactly one byte. + reg_num = arg30 + reg_txt = PDI.ctrl_reg_name.get(reg_num, 'r{:d}'.format(reg_num)) + reg_txt_terse = '{:d}'.format(reg_num) + self.insn_wr_counts = [1] + self.insn_rd_counts = [] + mnemonics = [ + 'Insn: STCS {:s}, i1'.format(reg_txt), + 'STCS {:s}, i1'.format(reg_txt), 'STCS', + ] + self.cmd_insn_parts_nice = ['STCS', reg_txt] + self.cmd_insn_parts_terse = ['STCS', reg_txt_terse] + elif opcode == PDI.OP_REPEAT: + # REPEAT: sets repeat count for the next instruction. + # Reads repeat count from following bytes. + width_data = arg10 + 1 + self.insn_wr_counts = [width_data] + self.insn_rd_counts = [] + mnemonics = [ + 'Insn: REPEAT i{:d}'.format(width_data), + 'REPEAT i{:d}'.format(width_data), 'REP', + ] + self.cmd_insn_parts_nice = ['REPEAT'] + self.cmd_insn_parts_terse = ['REP'] + elif opcode == PDI.OP_KEY: + # KEY: set activation key (enables PDIBUS mmap access). + # Writes a sequence of 8 bytes, fixed length. + width_data = 8 + self.insn_wr_counts = [width_data] + self.insn_rd_counts = [] + mnemonics = [ + 'Insn: KEY i{:d}'.format(width_data), + 'KEY i{:d}'.format(width_data), 'KEY', + ] + self.cmd_insn_parts_nice = ['KEY'] + self.cmd_insn_parts_terse = ['KEY'] + + # Emit an annotation for the instruction opcode. + self.put_ann_row_val(ss, es, Ann.OPCODE, mnemonics) + + # Prepare to write/read operands/data bytes. + self.insn_dat_bytes = [] + if self.insn_wr_counts: + self.insn_dat_count = self.insn_wr_counts[0] + return + if self.insn_rd_counts: + self.insn_dat_count = self.insn_rd_counts[0] + return + # FALLTHROUGH. + # When there are no operands or data bytes to read, + # then fall through to the end of the instruction + # handling below (which emits annotations). + + # Read bytes which carry operands (addresses, immediates) + # or data values for memory access. + if self.insn_dat_count and not is_break: + + # Accumulate received bytes until another multi byte + # data item is complete. + if not self.insn_dat_bytes: + self.insn_ss_data = ss + self.insn_dat_bytes.append(byteval) + self.insn_dat_count -= 1 + if self.insn_dat_count: + return + + # Determine the data item's duration and direction, + # "consume" its length spec (to simplify later steps). + data_ss = self.insn_ss_data + data_es = es + if self.insn_wr_counts: + data_ann = Ann.DATA_PROG + data_width = self.insn_wr_counts.pop(0) + elif self.insn_rd_counts: + data_ann = Ann.DATA_DEV + data_width = self.insn_rd_counts.pop(0) + + # PDI communicates multi-byte data items in little endian + # order. Get a nice textual representation of the number, + # wide and narrow for several zoom levels. + self.insn_dat_bytes.reverse() + data_txt_digits = ''.join(['{:02x}'.format(b) for b in self.insn_dat_bytes]) + data_txt_hex = '0x' + data_txt_digits + data_txt_prefix = 'Data: ' + data_txt_hex + data_txts = [data_txt_prefix, data_txt_hex, data_txt_digits] + self.insn_dat_bytes = [] + + # Emit an annotation for the data value. + self.put_ann_row_val(data_ss, data_es, data_ann, data_txts) + + # Collect detailled information which describes the whole + # command when combined (for a next layer annotation, + # spanning the complete command). + self.cmd_insn_parts_nice.append(data_txt_hex) + self.cmd_insn_parts_terse.append(data_txt_digits) + + # Send out write data first until exhausted, + # then drain expected read data. + if self.insn_wr_counts: + self.insn_dat_count = self.insn_wr_counts[0] + return + if self.insn_rd_counts: + self.insn_dat_count = self.insn_rd_counts[0] + return + + # FALLTHROUGH. + # When all operands and data bytes were seen, + # terminate the inspection of the instruction. + + # Postprocess the instruction after its operands were seen. + cmd_es = es + cmd_txt_nice = ' '.join(self.cmd_insn_parts_nice) + cmd_txt_terse = ' '.join(self.cmd_insn_parts_terse) + cmd_txts = [cmd_txt_nice, cmd_txt_terse] + self.put_ann_row_val(self.cmd_ss, cmd_es, Ann.COMMAND, cmd_txts) + if self.insn_opcode == PDI.OP_REPEAT and not is_break: + # The last communicated data item is the repeat + # count for the next instruction (i.e. it will + # execute N+1 times when "REPEAT N" is specified). + count = int(self.cmd_insn_parts_nice[-1], 0) + self.insn_rep_count = count + + # Have the state for instruction decoding cleared, but make sure + # to carry over REPEAT count specs between instructions. They + # start out as zero, will be setup by REPEAT instructions, need + # to get passed to the instruction which follows REPEAT. The + # instruction which sees a non-zero repeat count which will + # consume the counter and drop it to zero, then the counter + # remains at zero until the next REPEAT instruction. + save_rep_count = self.insn_rep_count + self.clear_insn() + self.insn_rep_count = save_rep_count + + def handle_bits(self, ss, es, bitval): + '''Handle a bit at the UART layer.''' + + # Concentrate annotation literals here for easier maintenance. + ann_class_text = { + Ann.START: ['Start bit', 'Start', 'S'], + Ann.PARITY_OK: ['Parity OK', 'Par OK', 'P'], + Ann.PARITY_ERR: ['Parity error', 'Par ERR', 'PE'], + Ann.STOP_OK: ['Stop bit', 'Stop', 'T'], + Ann.STOP_ERR: ['Stop bit error', 'Stop ERR', 'TE'], + Ann.BREAK: ['Break condition', 'BREAK', 'BRK'], + } + def put_uart_field(bitpos, annclass): + self.put_ann_data(bitpos, [annclass, ann_class_text[annclass]]) + + # The number of bits which form one UART frame. Note that + # the decoder operates with only one stop bit. + frame_bitcount = 1 + 8 + 1 + 1 + + # Detect adjacent runs of all-zero bits. This is meant + # to cope when BREAK conditions appear at any arbitrary + # position, it need not be "aligned" to an UART frame. + if bitval == 1: + self.zero_count = 0 + elif bitval == 0: + if not self.zero_count: + self.zero_ss = ss + self.zero_count += 1 + if self.zero_count == frame_bitcount: + self.break_ss = self.zero_ss + + # BREAK conditions are _at_minimum_ the length of a UART frame, but + # can span an arbitrary number of bit times. Track the "end sample" + # value of the last low bit we have seen, and emit the annotation only + # after the line went idle (high) again. Pass BREAK to the upper layer + # as well. When the line is low, BREAK still is pending. When the line + # is high, the current bit cannot be START, thus return from here. + if self.break_ss is not None: + if bitval == '0': + self.break_es = es + return + self.put(self.break_ss, self.break_es, self.out_ann, + [Ann.BREAK, ann_class_text[Ann.BREAK]]) + self.handle_byte(self.break_ss, self.break_es, None) + self.break_ss = None + self.break_es = None + self.bits = [] + return + + # Ignore high bits when waiting for START. + if not self.bits and bitval == 1: + return + + # Store individual bits and their start/end sample numbers, + # until a complete frame was received. + self.bits.append(Bit(bitval, ss, es)) + if len(self.bits) < frame_bitcount: + return + + # Get individual fields of the UART frame. + bits_num = sum([b.val << pos for pos, b in enumerate(self.bits)]) + if False: + # This logic could detect BREAK conditions which are aligned to + # UART frames. Which was obsoleted by the above detection at + # arbitrary positions. The code still can be useful to detect + # "other kinds of frame errors" which carry valid symbols for + # upper layers (the Atmel literature suggests "break", "delay", + # and "empty" symbols when PDI is communicated over different + # physical layers). + if bits_num == 0: # BREAK + self.break_ss = self.bits[0].ss + self.break_es = es + self.bits = [] + return + start_bit = bits_num & 0x01; bits_num >>= 1 + data_val = bits_num & 0xff; bits_num >>= 8 + data_text = '{:02x}'.format(data_val) + parity_bit = bits_num & 0x01; bits_num >>= 1 + stop_bit = bits_num & 0x01; bits_num >>= 1 + + # Check for frame errors. START _must_ have been low + # according to the above accumulation logic. + parity_ok = (bin(data_val).count('1') + parity_bit) % 2 == 0 + stop_ok = stop_bit == 1 + valid_frame = parity_ok and stop_ok + + # Emit annotations. + for idx in range(frame_bitcount): + self.put_ann_bit(idx, Ann.BIT) + put_uart_field(0, Ann.START) + self.put(self.bits[1].ss, self.bits[8].es, self.out_ann, + [Ann.DATA, ['Data: ' + data_text, 'D: ' + data_text, data_text]]) + put_uart_field(9, Ann.PARITY_OK if parity_ok else Ann.PARITY_ERR) + put_uart_field(10, Ann.STOP_OK if stop_ok else Ann.STOP_ERR) + + # Emit binary data stream. Have bytes interpreted at higher layers. + if valid_frame: + byte_ss, byte_es = self.bits[0].ss, self.bits[-1].es + self.put_bin_bytes(byte_ss, byte_es, Ann.BIN_BYTES, bytes([data_val])) + self.handle_byte(byte_ss, byte_es, data_val) + + # Reset internal state for the next frame. + self.bits = [] + + def find_clk_edge(self, samplenum, clock_pin, data_pin): + # Ignore the sample if the clock pin has not changed. + if clock_pin == self.prev_clock: + return + self.prev_clock = clock_pin + + # Sample the data line on rising clock edges. Always, for TX and for + # RX bytes alike. + if clock_pin == 1: + self.data_sample = data_pin + return + + # Falling clock edges are boundaries for bit slots. Inspect previously + # sampled bits on falling clock edges, when the start and end sample + # numbers were determined. Only inspect bit slots of known clock + # periods (avoid interpreting the DATA line when the "enabled" state + # has not yet been determined). + self.ss_last_fall = self.ss_curr_fall + self.ss_curr_fall = samplenum + if self.ss_last_fall is None: + return + + # Have the past bit slot processed. + bit_ss, bit_es = self.ss_last_fall, self.ss_curr_fall + bit_val = self.data_sample + self.handle_bits(bit_ss, bit_es, bit_val) + + def decode(self, ss, es, data): + for samplenum, pins in data: + + # Ignore identical samples. + if self.prev_pins == pins: + continue + self.prev_pins = pins + + # Have DATA processed at appropriate clock edges. + clock_pin, data_pin = pins[0], pins[1] + self.find_clk_edge(samplenum, clock_pin, data_pin)