TMS320F28P650DK: Questions about GSxRAM initialization after CPU1 watchdog reset

Ting,

I will refer back to the F28P65x TRM https://www.ti.com/lit/spruiz1b page 1045 which gives the boot flow

Ting-Wei Gao said:

(1) I use a CPU1 GSxRAM test variable, and add this variable by 1 per CPU1 PWM ISR.

     After I use CPU1 watchdog reset,  the variable will still remain its value.

     Is this phenomenon normal?

Ting-Wei Gao said:

(2) After power-on reset or CPU1 watchdog reset,

     will the variables in GSxRAM be set to zero if they don't have initial values in variable declaration?

A1/2)RAM INIT will only occur on a Power on reset(POR) or XRSn based reset.  Watchdog reset WDRSn will not trigger the RAM Init function in the Boot ROM.  So #1 is expected, and for #2 RAMINIT will only occur after POR, but not WDRSn.

Best,
Matthew

Yes, this what I was referring to.  Looking at the TRM page 774, you can also activate the RAM Init through a SW write to the DxInit/LxInit/GxInit registers and then wait for the Init to set the "DONE" bit.

Something you could do as part of your main code, is read the reset cause register "RESC" to determine if the source was something other than POR, and then init the RAMs accordingly.

Best,

Matthew

Ting-Wei, 

Good point on the c initialization, I see how that is an issue.  And yes, adding this code to code_start_branch.asm will address these issues and not impact the boot flow.  This section of code is the first thing that will get executed from a power up into flash boot, so there is no assumption of any CPU register retention, i.e. it is safe to code in assembly as you have done.

The only concern will be the watchdog, so I'm assuming you've disabled it via a WD_DISABLE = 1 predefine.  If you have any concerns on disabling the WD, we would need to add some more assembly to write to the check bits periodically.  If you've ran the above with WD_Enabled and don't see an issue, the RAM init time won't change run to run, so you can leave alone; I just don't know the time to RAM init the GSx RAM vs the WD timeout from reset.

Best,

Matthew