2.3.6.3 Authenticated Encrypted Initialization Data

The following formula calculates the additional time required for LSRAM to perform the encryption.

tLSRAM_enc = tLSRAM_pt + tLSRAM_auth + ((ROUNDUP((L × 2560) / 1024, 1) + 1) × 1024 × 8 / Dlsram) / 1000

Where, pt in "tLSRAM_pt" refers to "plaintext".

Important: Dlsram depends on the SPI SCK frequency.

The following table lists the LSRAM encrypted data divisor settings.

Table 2-1. LSRAM Encrypted Data Divisor Settings
SPI_SCK Frequency (MHz)Dlsram
13.33180
2030
4015

The following formula calculates the additional time required for USRAM to perform the encryption.

tUSRAM_enc = tUSRAM_pt + tUSRAM_auth + ((ROUNDUP((U × 2560) / 1024, 1) + 1) × 1024 × 8 / Dusram) / 1000

Where,

  • tLSRAM_pt = tLSRAM
  • tUSRAM_pt = tUSRAM
  • auth in "tLSRAM_auth" and "tUSRAM_auth" refers to "Authenticated Plaintext".
  • pt in "tUSRAM_pt" refers to "plaintext".
  • tLSRAM_auth = tUSRAM_auth = 103ms ± 6%.
Important: Dusram depends on the SPI SCK frequency.

The following table lists the USRAM encrypted data divisor settings.

Table 2-2. USRAM Encrypted Data Divisor Settings
SPI_SCK Frequency (MHz)Dusram
2045
4020

For SPI_SCK frequency of 13.3 MHz, the formula is as follows:

tUSRAM_enc = tUSRAM_pt + tUSRAM_auth + 0.01