TMS570LC4357: TMS570LC4357 PBIST: clarify precedence of ROM[1:0] vs ALGO (SPNU563A Table 9-14 / 9-15)

Hi mc,

mc b said:

Question 1 (directly verifiable): In Example 9.6.1, what would happen if we change only step 9 from ROM=0x3 to ROM=0x0, while keeping:

If you change only step 9 from ROM=0x3 to ROM=0x0 while keeping all other settings the same:

The PBIST would NOT execute properly. With ROM=0x0, the controller ignores all ROM-stored information about both algorithms and RAM groups.

When ROM=0x0:

• The controller will only use explicitly programmed values from ALGO and RINFOx registers
• However, it still needs ROM information to properly configure the test for specific RAM groups
• The PBIST controller requires ROM metadata to properly execute the algorithms against the specified RAM groups

The example sets ROM=0x3 specifically because the controller needs the ROM-stored configuration data to properly execute the March13N algorithm on the DCAN1 RAM.

mc b said:

Question 2 (precedence): When ROM includes “Algorithm information from ROM” (ROM=0x2 or ROM=0x3), does PBIST still use the ALGO register as the algorithm enable mask, or does ROM selection override/replace the ALGO selection?

When ROM includes "Algorithm information from ROM" (ROM=0x2 or ROM=0x3):

The ALGO register acts as an enable mask that selects from available ROM algorithms, not a replacement.

• The ALGO register selects which algorithms from ROM will be executed
• The ROM provides the implementation details of those algorithms
• Both are required: ALGO selects, ROM provides the algorithm details

The apparent contradiction in Example 9.6.1 exists because:

1. First, you select the algorithm via ALGO register (March13N = 0x00000004)
2. Then, you enable ROM information via ROM=0x3
3. The controller uses your ALGO selection to determine which ROM-defined algorithm to execute

--
Thanks & regards,
Jagadish.

Hi Jagadish,

Thanks for the explanation.

I still see one ambiguity that is important for us from a safety perspective (TMS570LC4357, application PBIST):

1) Is ROM = 0x0 a *supported* and *fully specified* configuration for application code on TMS570LC4357, or should it be considered "not supported / internal only"?

   - The TRM (SPNU563A, Table 9-14) describes ROM=0 as "No information is used from ROM".
   - However, from your answer and from Example 9.6.1 behavior, it sounds like ROM=0 cannot be used to run a valid PBIST test because the controller still depends on ROM metadata to interpret ALGO and RINFOx.

   Can you please confirm explicitly:
   - On TMS570LC4357, is there any valid PBIST test configuration where ROM=0 is intended to be used by application software?
   - Or should ROM=0 be treated as an unsupported mode (e.g. only for manufacturing / internal test), and thus not used in customer software?

2) For safety-related documentation and reviews, we want to use a clear rule like:
   - "For application PBIST, always set ROM = 0x3. Other ROM values are not to be used."

   Is this rule correct and acceptable from TI’s point of view for TMS570LC4357?

3) Finally, could TI please clarify (or confirm) the intended precedence in the TRM:
   - When ROM indicates "algorithm information from ROM" (ROM=2 or 3), ALGO is still the *enable mask* that selects which algorithms to run, and ROM merely defines those algorithms (i.e., ROM does not override ALGO selection). Is this correct?

If possible, it would be very helpful if this could be clarified in an app note or a TRM update/errata, since this affects how we justify our PBIST configuration in safety documentation.

Best regards,
Mehmet Can

Hi Mehmet Can,

1. Regarding ROM = 0x0 Configuration:

Explicit confirmation: ROM=0x0 should be treated as not supported for application software on the TMS570LC4357.

While the TRM technically describes ROM=0 as "No information is used from ROM," this configuration:

• Is not demonstrated in any application examples
• Cannot properly execute PBIST tests as the controller requires ROM metadata
• Is likely reserved for specialized manufacturing or internal test purposes

The controller architecture fundamentally relies on ROM-based algorithm definitions to properly execute tests, even when ALGO and RINFOx registers are explicitly configured.

2. Safety Related Rule Confirmation:

Yes, your proposed rule is correct and aligns with TI's recommendations:

For application PBIST, always set ROM = 0x3. Other ROM values are not to be used.

This rule:

• Matches TI's recommended configuration in Example 9.6.1
• Ensures proper operation of the PBIST controller

3. Precedence Confirmation:

Correct understanding: When ROM=2 or ROM=3 (algorithm information from ROM):

• ALGO acts as an enable mask that selects which algorithms to run
• ROM defines the algorithms but does not override the ALGO selection
• Both registers work together: ROM provides the algorithm definitions, ALGO enables specific algorithms

--
Thanks & regards,
Jagadish.