bios/sdram: improve bitslip selection when window can't be optimal (not enough taps...

diff --git a/litex/soc/software/bios/sdram.c b/litex/soc/software/bios/sdram.c
index 4575156973fd28fd55330260a229682625b93520..cd06491a0de6a60fb91f0eb0b21ef2c1f217d195 100644 (file)
--- a/litex/soc/software/bios/sdram.c
+++ b/litex/soc/software/bios/sdram.c
@@ -377,6 +377,7 @@ static int read_level_scan(int silent)
        unsigned char prs[DFII_NPHASES*DFII_PIX_DATA_SIZE];
        int p, i, j;
        int working;
+       int working_delays;
        int optimal;
 
        if (!silent)
@@ -407,6 +408,7 @@ static int read_level_scan(int silent)
        sdram_dfii_pird_address_write(0);
        sdram_dfii_pird_baddress_write(0);
        working = 0;
+       working_delays = 0;
        optimal = 1;
        for(i=DFII_PIX_DATA_SIZE/2-1;i>=0;i--) {
                if (!silent)
@@ -425,6 +427,7 @@ static int read_level_scan(int silent)
                                        working_delay = 0;
                        }
                        working |= working_delay;
+                       working_delays += working_delay;
                        if ((j == 0) || (j == (ERR_DDRPHY_DELAY-1)))
                                /* to have an optimal scan, first tap and last tap should not be working */
                                optimal &= (working_delay == 0);
@@ -442,7 +445,8 @@ static int read_level_scan(int silent)
        command_p0(DFII_COMMAND_RAS|DFII_COMMAND_WE|DFII_COMMAND_CS);
        cdelay(15);
 
-       return working & optimal;
+       /* Successful if working and optimal or if number of working delays > 3/4 of the taps */
+       return (working & optimal) | (working_delays > 3*ERR_DDRPHY_DELAY/4);
 }
 
 static void read_level(void)