[asterisk-dev] TDM400P FXS polarity reversal method.

[Alec Davis]

The wctdm code specifically has code to set an FXS module to reverse the
line voltage, the code I refer to is a module parameter 'reversepolarity'.
When I " echo 1 > /sys/module/wctdm/parameters/reversepolarity" the line
succesfully changes from -48V to +48V

But when attempting to use the VSGN bit 6 (Register 72) from the Si3215
datasheet which sets the VTip-VRing polarity, when I set this bit the
On-Hook voltage changes from -48v to +9.5v, not +48V as expected.

        if (vmwilamp){						  /* Visual Message Waiting Indicator */
                wctdm_setreg(wc, card, 72, 0x60);       /* reverse line
voltage*/
        } else {
                wctdm_setreg(wc, card, 72, 0x20);       /* normal line */
        }

Can someone explain if the reversepolarity code is a workaround for the
TDM400P FXS module not properly supporting the VSGN method.

The wctdm24xxp code doesn't have a reversepolarity module parameter, does it
correctly support being controlled by the VSGN bit, or does it need the
extra code that the wctdm has?

Alec Davis