Logic Analyzer core: Trigger Sequence States

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Sequence states allow you to control how the analyzer evaluates and stores sampled data. Each state gives you control over data capturing, searching for a target (optionally multiple times), or branching to another sequence should a special condition occur. On a hit, the analyzer advances to the next sequence state. It can also trigger the analyzer controller & start/stop timers. With 16 sequence states, you can create complex protocol following triggers.


Figure 24 - Example Sequence Level

For each state you specify:

  • Capture Term (sum of trigger terms, range checks, edge detect & timer hits)
  • Hit Term (sum of trigger terms, range checks, edge detect & timer hits)
  • Else Term (sum of trigger terms, range checks, edge detect & timer hits)
  • Occurrence Count
  • Else State
  • Timer Control Flags (start/stop/clear for timers 1 & 2)
  • Trigger Flag

The trigger sequencer itself is a relatively simple state machine. Pseudocode for it is:

if (sampled_input valid) then {
    if (capture_term valid) then
        capture data
    if (hit_term valid) then {
        increment hit_count
        if (hit_count == fsm_occurence_count) then {    
            reset hit_count
            if (fsm_trigger || last_state) then assert run to controller
            if (!last_state && !fsm_last_state) advance to next state
    otherwise if (else_term valid) then {
        reset hit_count
        go to state "fsm_else_level"

Figure 25 - Trigger Sequencer State Machine

8.1 Example (Trigger Sequence Initialization)

#define TRIGSTATE_STOP_TIMER0  0x01000000
#define TRIGSTATE_STOP_TIMER1  0x02000000
#define TRIGSTATE_CLEAR_TIMER0 0x04000000
#define TRIGSTATE_CLEAR_TIMER1 0x08000000
#define TRIGSTATE_START_TIMER0 0x10000000
#define TRIGSTATE_START_TIMER1 0x20000000
#define TRIGSTATE_TRIGGER_FLAG 0x40000000
#define TRIGSTATE_LASTSTATE    0x80000000
void write_trigger_state (
  int statenum,     // 0 to 15
  int last_state,
  int set_trigger,
  int start_timer,  // bit0=timer1, bit1=timer2
  int stop_timer,   // bit0=timer1, bit1=timer2
  int clear_timer,  // bit0=timer1, bit1=timer2
  int else_state,   // 0 to 15
  int obtain_count)
  write_select (statenum & TRIGSTATE_STATENUM_MASK);
  unsigned int value =
    (obtain_count & TRIGSTATE_OBTAIN_MASK);
  if (last_state) value |= TRIGGER_LASTSTATE;
  if (set_trigger) value |= TRIGSTATE_TRIGGER_FLAG;
  if (start_timer & 1) value |= TRIGSTATE_START_TIMER0;
  if (start_timer & 2) value |= TRIGSTATE_START_TIMER1;
  if (stop_timer & 1) value |= TRIGSTATE_STOP_TIMER0;
  if (stop_timer & 2) value |= TRIGSTATE_STOP_TIMER1;
  if (clear_timer & 1) value |= TRIGSTATE_CLEAR_TIMER0;
  if (clear_timer & 2) value |= TRIGSTATE_CLEAR_TIMER1;
  write_chain (value);

Figure 26 - Initialize Trigger Sequence

License note

This document is Copyright © 2011 Ian Davis
Released under the  GNU General Public License