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non-optimized strawman for improved bootrom ECC reads #8

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non-optimized strawman for improved bootrom ECC reads #8

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27 changes: 27 additions & 0 deletions src/main/arm/varm_otp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -390,7 +390,34 @@ int __used s_varm_api_hx_otp_access(aligned4_uint8_t *buf, uint32_t buf_len, otp
// note: we expect user to verify the data was written correctly
} else {
if (is_ecc) {
// current_val holds the raw value
*(uint16_t *)buf = inline_s_otp_read_ecc(row);
// when reading using bootrom, validate the ECC read corresponds
// to the raw value read above. Otherwise, the data is corrupted.
uint32_t re_encoded = s_otp_calculate_ecc(*(uint16_t *)buf);
uint32_t current_wo_brp = (current_value & 0x3FFFFFu);
if ((current_val & 0xC00000u) == 0x0) &&
(__builtin_popcount(current_wo_brp ^ re_encoded) >= 1)) {
// If neither BRP bit is set, then if there is more than
// a single-bit error, the data from the ECC read is corrupted.
rc = BOOTROM_ERROR_INVALID_DATA;
goto abort;
} else if ((current_val & 0xC00000u) == 0xC00000u) &&
(__builtin_popcount(((~current_wo_brp) & 0x3FFFFFu) ^ re_encoded) >= 1)) {
// If both BRP bits are set, then if there is more than
// a single-bit error, the data from the ECC read is corrupted.
rc = BOOTROM_ERROR_INVALID_DATA;
goto abort;
} else {
// When only one BRP bit is set, allow up to a single-bit error
// vs. either inverted or original current raw value (w/o BRP).
if ((__builtin_popcount(current_wo_brp ^ re_encoded) >= 1) &&
(__builtin_popcount(((~current_wo_brp) & 0x3FFFFFu)^ re_encoded) >= 1)) {
rc = BOOTROM_ERROR_INVALID_DATA;
goto abort;
}
}
// if did not abort from above checks, then value already stored in buf.
} else {
*(uint32_t *)buf = current_val;
}
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