secded_edac

extras/secded_edac.vhdl

Description

This package implements Single Error Correction, Double Error Detection (SECDED) by extending the Hamming code with an extra overall parity bit. It is built on top of the functions implemented in hamming_edac. The ecc_vector is extended with an additional parity bit to the right of the Hamming parity as shown below.

SECDED ecc_vector layout:

                           MSb            LSb
[(data'length - 1) <-> 0] [-1 <-> -(parity_size - 1)] [-parity_size]
          data               Hamming parity          SECDED parity bit

Example usage

signal word, corrected_word : std_ulogic_vector(15 downto 0);
constant WORD_MSG_SIZE : positive := secded_message_size(word'length);
signal secded_word :
  ecc_vector(word'high downto -secded_parity_size(WORD_MSG_SIZE));
...
secded_word <= secded_encode(word);
... <SEU or transmission error flips a bit>
corrected_word <= secded_decode(hamming_word);
errors := secded_has_errors(secded_word);
if errors(single_bit) or errors(double_bit) then ... -- check for error

As with hamming_edac, it is possible to share logic between the decoder and error checker and also between an encoder and decoder that don’t operate simultaneously. Refer to hamming_edac and secded_codec for examples of this approach.

Types

secded_edac.secded_error_kind

Type of SECDED errors.

secded_edac.secded_errors

Boolean bitfield for SECDED errors.

Subprograms

secded_edac.secded_message_size (Data_size : positive) → positive
Determine the size of a message (data interleaved with parity) given the size of data to be protected.
Parameters:
  • Data_size (positive) – Number of data bits
Returns:

Message size.
secded_edac.secded_indices (Data_size : positive) → ecc_range
Return the left and right indices needed to declare an ecc_vector for the requested data size.
Parameters:
  • Data_size (positive) – Number of data bits
Returns:

Range with left and right.
secded_edac.secded_parity_size (Message_size : positive) → positive
Determine the number of parity bits for a given message size.
Parameters:
  • Message_size (positive) – Number of bits in complete message
Returns:

Parity size.
secded_edac.secded_data_size (Message_size : positive) → positive
Determine the number of data bits for a given message size.
Parameters:
  • Message_size (positive) – Number of bits in complete message
Returns:

Data size.
secded_edac.secded_encode (Data : std_ulogic_vector) → ecc_vector
Encode the supplied data into an ecc_vector using Hamming code for the parity and an additional overall parity for SECDED. This version uses self contained logic.
Parameters:
  • Data (std_ulogic_vector) – Raw data
Returns:

Encoded data with parity.
secded_edac.secded_encode (Data : std_ulogic_vector; Parity_bits : unsigned) → ecc_vector
Encode the supplied data into an ecc_vector using Hamming code for the parity and an additional overall parity for SECDED. This version depends on external logic to generate the Hamming parity bits.
Parameters:
  • Data (std_ulogic_vector) – Raw data
  • Parity_bits (unsigned) – Number of parity bits
Returns:

Encoded data with parity.
secded_edac.secded_decode (Encoded_data : ecc_vector) → std_ulogic_vector
Decode an ecc_vector into the plain data bits, potentially correcting a single-bit error if a bit has flipped. This version uses self contained logic.
Parameters:
  • Encoded_data (ecc_vector) – Encoded (uninterleaved) message
Returns:

Decoded data.
secded_edac.secded_has_errors (Encoded_data : ecc_vector) → secded_errors
Test for a single-bit and double-bit errors in an ecc_vector. Returns true for each error type.
Parameters:
  • Encoded_data (ecc_vector) – Encoded (uninterleaved) message
Returns:

true if message has a single or double-bit error.
secded_edac.secded_has_errors (Encoded_data : ecc_vector; Syndrome : unsigned) → secded_errors
Test for a single-bit and double-bit errors in an ecc_vector. Returns true for each error type. This version depends on external logic to generate a syndrome.
Parameters:
  • Encoded_data (ecc_vector) – Encoded (uninterleaved) message
  • Syndrome (unsigned) – Syndrome generated by hamming_parity()
Returns:

true if message has a single or double-bit error.