129 IEEE MBIST & ECC for RAM 8x32 :: Quicker, easier and cheaper to make your own chip!

How it works

RAM: only 8x32 bit data available, but this RAM designed 8x40 for ECC implement

MBIST (Memory Built-In Self-Test): using March algorithm. In this project, I decided using March C-:

↑ (w0)
↑ (r0,w1)
↑ (r1,w0)
↓ (r0,w1)
↓ (r1,w0)
↓ (r0)

Hamming ECC (Hamming Error Correcting Code) SECDED:
We add r parity bits such that: 2^r = m+r+1
where:
m = number of data bits
r = number of parity bits
Parity bits are placed at power-of-two positions
Each parity bit monitors a specific subset of bits:

P1 checks all bits with LSB = 1: 1,3,5,7,…
P2 checks bits with second LSB = 1: 2,3,6,7,…
P4 checks bits with third LSB = 1: 4,5,6,7,12,13,…
… and so on
When reading data, parity bits are recalculated and compared with the stored parity bits.

Run and expected results:

Input ui[0] MBIST Enable:

MBIST Enable == 0: Normal Mode
MBIST Enable == 1: Start RAM test

Output uo[0] MBIST Activated:

MBIST Activated == 0: MBIST mode is not enbled
MBIST Activated == 1: MBIST mode is enbled

Output uo[1] MBIST Fail:

Can only be toggled when MBIST Activated == 1
Inversion of uo[2] indicates MBIST Pass
MBIST Fail == 0: MBIST mode has not failed
MBIST Fail == 1: MBIST mode has failed

Output uo[2] MBIST Pass:

Can only be toggled when MBIST Activated == 1
Inversion of uo[1] indicates MBIST Fail
MBIST Fail == 0: MBIST mode has not passed
MBIST Fail == 1: MBIST mode has passed
Side note: After ui[0] MBIST Enable == 1, only one uo[1] MBIST Fail or uo[2] MBIST Pass can be toggled

Output uo[3] RAM Enable:

Check if RAM is enable or not
RAM Enable == 0: RAM is not enable
RAM Enable == 1: RAM is enable

Output uo[4] ECC Bypass Status:

Can only be toggled when MBIST Activated == 1
ECC Bypass Status == 0: ECC is not bypassed
ECC Bypass Status == 1: ECC is now bypassed

Output uo[5] ECC Single Bit Error Detected:

ECC Single Bit Error Dtected == 0: No error found
ECC Single Bit Error Detected == 1: 1 Error Detected, fix status will be shown in uo[7]

Output uo[6] ECC Double Bit Error Detected:

ECC Double Bit Error Dtected == 0: No error found
ECC Double Bit Error Detected == 1: 2 Error Detected, cannot be fix

Output uo[7] ECC Single Bit Error Fix:

ECC Single Bit Error Fix == 0: No error found
ECC Single Bit Error Fix == 1: 1 Error Detected, fixed

How to test

ECC and MBIST test are the same, they have 2 parts:

Functional Check: Check if normal function of DUT is working
Fault injection: simulation error to watch behaviors of DUT

All test have checker

External hardware

All built-in, we are all in-house, no need to outsource, because we are strong enough

#	Input	Output
0	MBIST Enable	[MBIST] Activated
1		[MBIST] Fail
2		[MBIST] Pass
3		RAM Enable
4		ECC Bypass Status
5		[ECC] Single Bit Error Detected
6		[ECC] Double Bit Error Detected
7		[ECC] Single Bit Error Fix

129 IEEE MBIST & ECC for RAM 8x32