CRITICALITY

Medium

DESCRIPTION

The DSP may hang after multiple iterations of going into C66x Corepac Power Down and wake up from external events.

The C66x XMC (External Memory Controller) can have outstanding pre-fetch requests when C66x Corepac transitions to a Power Down state. The XMC clocks are gated internally during this transition. While XMC clocks are gated, outstanding pre-fetch request responses are not seen by the XMC which leads to an inconsistent state between the XMC and the L3 Interconnect. When the DSP wakes up, this can manifest as different symptoms within the DSP subsystem, including Cache corruption, incorrect data being returned to the CPU, and can eventually lead to a DSP hang condition.

WORKAROUND

The steps to avoid this issue are as given below:

1. Ensure the code which places the DSP C66x Corepac to Power Down State (power down entry procedure shown below) is placed in the DSP C66x L2 RAM memory.
2. Set the IDLE bit in PDCCMD register during initialization.
3. Inside the power down entry procedure include the following software sequence:
   1. Execute MFENCE instruction.
   2. Write 1 to XPFCMD.INV (address 0x0800_0300).
   3. Read XPFACS (address 0x0800_0304).
   4. Execute IDLE instruction.

While executing multi-threaded DSP software with C66x Corepac Power Down caution should be observed to not allow the power down entry sequence to be preempted and switch context.

The software developer can choose to not perform the above software sequence by never enabling the DSP C66x Pre-fetch. The developer should understand the impact of not enabling DSP Pre-fetch on the DSP CPU memory access performance in their application.

REVISIONS IMPACTED

SR 2.0, 1.1, 1.0

TDA2x: 2.0, 1.1, 1.0

DRA75x, DRA74x: 2.0, 1.1, 1.0

AM572x: 2.0, 1.1