STM32H573 : RNG Seed Error (SEIS) when used with TZEN=1 and STiRoT

hicham75 · ‎2025-01-10

Hi,

I try to use PKA for some ECDSA computation. For this purpose I needed to use PKA block. However, in SR register, I never get INITOK bit set.

I am working with TrustZone enabled. So, STiRoT is executed before my program.

After investigation, I've seen that bit SEIS in RNG_SR is set. (while CEIS=0)

Despite reference manual stating in this case, it means some thing went wrong and RNG was able to auto-reset and recover, I think this is what is preventing PKA INITOK to be set.

"INITOK: PKA initialization OK
This bit is asserted when PKA initialization is complete. When RNG is not able to output proper
random numbers INITOK stays at 0."

With same program and with TrustZone disabled(Hence, STiRoT is not executed), RNG is correctly configured without any SEIS error and PKA INITOK bit is set.

I am using RNG in A configuration.

RNG = {
  CR = 0xf00e04,
  SR = 0x41,
  DR = 0x31b4c84e,
  NSCR = 0x3af66,
  HTCR = 0x6a91
}

HCLK(AHB2) is 250 Mhz and HSI48 is used for RNG sampling.

Could someone help with this issue or point any additional configuration to be checked?

Regards