topic Re: etpu_set4 pwmmac clarification in MPC5xxx

etpu_set4 pwmmac clarification

jyothsna_rajan — Wed, 11 Aug 2021 00:48:04 GMT

Hi, In the etpu-set4 pwmmac sample application half-cycle reload option is specified. Where can I find more details of when cycle reload is typically used?

Is there an application note that demonstrates how to invoke and use the pwmmac functions?

Refer the attached etpuc_pwmmac.c, the specific section shown below:

//====== begin excerpt

else if ( (m2 == 1) && (flag0 == 1) )
{
.....
// set channelX half-cycle reload flag
tmp_half_reload_flag__master_chan = 0x800000 + GetCurrentChanNum()
......
goto PWMMAC_RELOAD;
}

//=============== end excerpt

The param 'tmp_half_reload_flag__master_chan' appears to be a flag but is manipulated using channel number. What is rationale behind this?

Thank you for taking time to clarify.

Best, JR

Re: etpu_set4 pwmmac clarification

davidtosenovjan — Thu, 12 Aug 2021 11:16:56 GMT

The function is described in the following appnote:

https://www.nxp.com/docs/en/application-note/AN2969.pdf

Mentioned feature is described in section 3.4.

Half cycle update has faster response, on the other hand it’ll have higher etpu load i.e. performance limits.

Regarding source code - it seems mentioned flag tmp_half_reload_flag__master_chan (it is alias for register B) has an effect on channel switching.

Are you going to modify or re-use eTPU source code?

Re: etpu_set4 pwmmac clarification

johndiener — Thu, 12 Aug 2021 17:52:30 GMT

Just adding a couple of notes to David's excellent info:
- tmp_half_reload_flag__master_chan is used to retain the master channel number in order to channel context switch in PWMMACReloadPhase(), and then restore proper channel context at return time. It also passes a flag indicating reload or half reload cycle into the routine.
- as mentioned, this is an alias of register B... if modifying C code that uses register aliasing it is recommended to take special care and carefully analyze and test the results of any changes.