[etherlab-users] stack overflow

Luigjes, Godert gluigjes at moog.com
Tue Sep 15 14:17:56 CEST 2015

HI all,

I am evaluating a HBM CX27 EtherCAT data aquisition system.
It has, at least for me unusal way of configuring the PDO map.
Each input signal, and its corresponding data signal occupies
two 'ec_pdo_info_t' entries.

To clearify, 'ethercat cstruct' looks like this:

ec_pdo_entry_info_t slave_10_pdo_entries[] = {
    {0x6130, 0x01, 32},
    {0x6150, 0x01, 8},
    {0x6130, 0x02, 32},
    {0x6150, 0x02, 8},
    {0x6130, 0xc7, 32},
    {0x6150, 0xc7, 8},
    {0x61d1, 0x02, 64},
    {0x61d1, 0x03, 64},
    {0x61e1, 0x01, 64},

ec_pdo_info_t slave_10_pdos[] = {
    {0x1a00, 2, slave_10_pdo_entries + 0},
    {0x1a01, 2, slave_10_pdo_entries + 2},
    {0x1a02, 2, slave_10_pdo_entries + 4},
    {0x1a03, 2, slave_10_pdo_entries + 6},
    {0x1a04, 2, slave_10_pdo_entries + 8},
    {0x1ac8, 1, slave_10_pdo_entries + 399},
    {0x1ac9, 1, slave_10_pdo_entries + 400},
    {0x1aca, 1, slave_10_pdo_entries + 401},

As you can see it can handle loads of data signals.
The problem is that during configuration of the device
I get a stack overflow.

I have instrumented some code in fsm_pdo.c, showing the actual free stack space.

-- Function: ec_fsm_pdo_conf_action_pdo_mapping  stack free: 0x00001be0
-- Function: ec_fsm_pdo_conf_action_check_mapping  stack free: 0x00001b6c
-- Function: ec_fsm_pdo_conf_action_pdo_mapping  stack free: 0x00001b4c
-- Function: ec_fsm_pdo_conf_action_check_mapping  stack free: 0x00001b4c
-- Function: ec_fsm_pdo_conf_action_pdo_mapping  stack free: 0x0000006c
-- Function: ec_fsm_pdo_conf_action_check_mapping  stack free: 0x0000003c
-- Function: ec_fsm_pdo_conf_action_pdo_mapping  stack free: 0x0000001c
-- Function: ec_fsm_pdo_conf_action_check_mapping  stack free: 0x00000004
-- Function: ec_fsm_pdoBUG: unable to handle kernel paging request at 696c610a

There seems to be some recursion going on, eating the stack and crashing the application.

If the HBM is cold-started, it has no configuration and the code does not
go into recusion. It probably uses the escape route in
ec_fsm_pdo_conf_action_pdo_mapping() where the list_empty() exits the function.
If the application is restarted without a power cycle on the HBM unit
it enters the recursion and crashes.

For now I have a work around this problem. Default the SII-EEPROM does not have
'enable_pdo_configuration' bit set, in CoE details. When I enable this bit, the
code uses the escape in 'ec_fsm_pdo_conf_action_check_mapping' and exits via

For now this seems to work. I have to double check if I get all my data.
At least the application does not crash anymore.

Godert Luigjes,
Software Engineer, Moog Inc.

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