olo_ft_pkg_ecc¶

Status Information¶

Description¶

This package contains SECDED (Single Error Correction, Double Error Detection) Hamming code functions used internally by the ECC-protected entities in the ft area (e.g. olo_ft_ram_sp).

For the SECDED scheme overview, codeword layout and overhead table, see Open Logic Fault-Tolerance Principles.

All functions in this package are synthesizable; there are no testbench-only helpers. They split into two categories:

Elaboration-time helpers — eccParityBits and eccCodewordWidth are pure integer functions of a positive argument. Their typical use is to size ports and signals from a generic data width (e.g. signal Codeword : std_logic_vector(eccCodewordWidth(Width_g) - 1 downto 0);). They evaluate to a constant at elaboration and produce no logic.
Combinational RTL logic — eccEncode, eccSyndromeAndParity, eccCorrectData, eccSecError and eccDedError operate on signals in the read/write datapath. They synthesize to combinational logic (XOR trees and selection).

Functions¶

eccParityBits¶

function eccParityBits (
    DataWidth : positive
) return positive;

Returns the number of Hamming parity bits required for a given data width (excluding the overall parity bit). Computed as the smallest m such that 2^m >= DataWidth + m + 1.

Usage: Synthesizable, elaboration-time helper. Typical use is to size signals/ports from a generic.

eccCodewordWidth¶

function eccCodewordWidth (
    DataWidth : positive
) return positive;

Returns the total codeword width including data bits, Hamming parity bits, and the overall parity bit. Equivalent to DataWidth + eccParityBits(DataWidth) + 1.

Usage: Synthesizable, elaboration-time helper. Typical use is to size signals/ports from a generic.

eccEncode¶

function eccEncode (
    Data : std_logic_vector
) return std_logic_vector;

Encodes a data word into a SECDED codeword. Bit 0 of the result is the overall parity bit; bits at power-of-2 positions (1, 2, 4, 8, ...) are Hamming parity bits; remaining positions hold the data bits.

Usage: Synthesizable, combinational. Used on the write path to produce the codeword stored in memory.

eccSyndromeAndParity¶

function eccSyndromeAndParity (
    Codeword  : std_logic_vector;
    DataWidth : positive
) return std_logic_vector;

Computes the syndrome and overall parity from a (possibly corrupted) codeword. The result packs both into one vector: bits ParityBits-1 downto 0 hold the syndrome, bit ParityBits holds the overall parity error. Result intended to be fed into eccCorrectData, eccSecError, and eccDedError.

Usage: Synthesizable, combinational. Used on the read path before the optional ECC pipeline registers.

eccCorrectData¶

function eccCorrectData (
    Codeword  : std_logic_vector;
    SynPar    : std_logic_vector;
    DataWidth : positive
) return std_logic_vector;

Extracts the corrected data bits from a codeword using the precomputed syndrome/parity from eccSyndromeAndParity. When a single-bit error is detected (overall parity odd, syndrome nonzero), the offending bit is corrected before extraction.

Usage: Synthesizable, combinational. Used on the read path to drive the corrected data output.

eccSecError¶

function eccSecError (
    SynPar : std_logic_vector
) return std_logic;

Returns '1' when a single-bit error was corrected. Under SECDED assumption (at most two bit errors per codeword), an odd overall parity bit indicates a single-bit error.

Usage: Synthesizable, combinational. Drives the SEC status output.

eccDedError¶

function eccDedError (
    SynPar : std_logic_vector
) return std_logic;

Returns '1' when a double-bit error was detected. A nonzero syndrome combined with even overall parity indicates two bit errors, which SECDED can detect but not correct.

Usage: Synthesizable, combinational. Drives the DED status output.