soc/software/bios/sdram: improve write_level robustness

diff --git a/litex/soc/software/bios/sdram.c b/litex/soc/software/bios/sdram.c
index eb8dda036b55bde56fd212e819ac6ab93fed2a7d..d3d07583a84550a2baaed3707b9e13d68ea2aa69 100644 (file)
--- a/litex/soc/software/bios/sdram.c
+++ b/litex/soc/software/bios/sdram.c
@@ -277,13 +277,14 @@ int write_level(void)
        unsigned char taps_scan[ERR_DDRPHY_DELAY];
 
        int one_window_active;
-       int one_window_start;
+       int one_window_start, one_window_best_start;
+       int one_window_count, one_window_best_count;
 
        int delays[NBMODULES];
 
-    int ok;
+       int ok;
 
-       err_ddrphy_wdly = (ERR_DDRPHY_DELAY*14)/16 - ddrphy_half_sys8x_taps_read();
+       err_ddrphy_wdly = ERR_DDRPHY_DELAY - ddrphy_half_sys8x_taps_read();
 
        printf("Write leveling:\n");
 
@@ -291,12 +292,12 @@ int write_level(void)
        cdelay(100);
        for(i=0;i<NBMODULES;i++) {
                printf("m%d: |", i);
-           dq_address = sdram_dfii_pix_rddata_addr[0]+4*(NBMODULES-1-i);
+               dq_address = sdram_dfii_pix_rddata_addr[0]+4*(NBMODULES-1-i);
 
                /* rst delay */
                write_delay_rst(i);
 
-               /* scan taps */
+               /* scan write delay taps */
                for(j=0;j<err_ddrphy_wdly;j++) {
                        int zero_count = 0;
                        int one_count = 0;
@@ -324,14 +325,23 @@ int write_level(void)
                }
                printf("|");
 
-               /* select last 0/1 transition */
+               /* find longer 1 window and set delay at the 0/1 transition */
                one_window_active = 0;
                one_window_start = 0;
+               one_window_count = 0;
+               one_window_best_start = 0;
+               one_window_best_count = 0;
                delays[i] = -1;
                for(j=0;j<err_ddrphy_wdly;j++) {
                        if (one_window_active) {
-                               if (taps_scan[j] == 0)
+                               if ((taps_scan[j] == 0) | (j == err_ddrphy_wdly - 1)) {
                                        one_window_active = 0;
+                                       one_window_count = j - one_window_start;
+                                       if (one_window_count > one_window_best_count) {
+                                               one_window_best_start = one_window_start;
+                                               one_window_best_count = one_window_count;
+                                       }
+                               }
                        } else {
                                if (taps_scan[j]) {
                                        one_window_active = 1;
@@ -339,7 +349,7 @@ int write_level(void)
                                }
                        }
                }
-               delays[i] = one_window_start;
+               delays[i] = one_window_best_start;
 
                /* configure write delay */
                write_delay_rst(i);