From cd89b62ff65a3eaba78a05b6b15d51835adc7bac Mon Sep 17 00:00:00 2001
From: Maciej Dudek <mdudek@antmicro.com>
Date: Wed, 25 Jan 2023 11:35:20 +0100
Subject: [PATCH] liblitedram: Fix LFSR

LFSR only returns 1 random bit per lfsr() call,
so we should concatenate 8 consecutive calls to obtain 1 random byte

Signed-off-by: Maciej Dudek <mdudek@antmicro.com>
---
 litex/soc/software/liblitedram/sdram.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/litex/soc/software/liblitedram/sdram.c b/litex/soc/software/liblitedram/sdram.c
index 86cdfa303..aea05759e 100644
--- a/litex/soc/software/liblitedram/sdram.c
+++ b/litex/soc/software/liblitedram/sdram.c
@@ -301,9 +301,10 @@ static void print_scan_errors(unsigned int errors) {
 #define MODULE_BITMASK ((1<<SDRAM_PHY_DQ_DQS_RATIO)-1)
 
 static unsigned int sdram_write_read_check_test_pattern(int module, unsigned int seed) {
-	int p, i;
+	int p, i, bit;
 	unsigned int errors;
 	unsigned int prv;
+	unsigned char value;
 	unsigned char tst[DFII_PIX_DATA_BYTES];
 	unsigned char prs[SDRAM_PHY_PHASES][DFII_PIX_DATA_BYTES];
 
@@ -311,8 +312,12 @@ static unsigned int sdram_write_read_check_test_pattern(int module, unsigned int
 	prv = seed;
 	for(p=0;p<SDRAM_PHY_PHASES;p++) {
 		for(i=0;i<DFII_PIX_DATA_BYTES;i++) {
-			prv = lfsr(32, prv);
-			prs[p][i] = prv;
+			value = 0;
+			for (bit=0;bit<8;bit++) {
+				prv = lfsr(32, prv);
+				value |= (prv&1) << bit;
+			}
+			prs[p][i] = value;
 		}
 	}