diff --git a/artiq/firmware/libboard/sdram.rs b/artiq/firmware/libboard/sdram.rs
index f2b320c93..f987ab79c 100644
--- a/artiq/firmware/libboard/sdram.rs
+++ b/artiq/firmware/libboard/sdram.rs
@@ -177,17 +177,19 @@ mod ddr {
             let delay = Cell::new(0);
             let incr_delay_until = |expected| {
                 while delay.get() < DDRPHY_MAX_DELAY {
-                    sdram_phy::command_prd(DFII_COMMAND_CAS|DFII_COMMAND_CS|
-                                           DFII_COMMAND_RDDATA);
-                    spin_cycles(15);
-
                     let mut working = true;
-                    for p in 0..DFII_NPHASES {
-                        for &offset in [n, n + DQS_SIGNAL_COUNT].iter() {
-                            let addr = DFII_PIX_RDDATA_ADDR[p].offset(offset as isize);
-                            let data = prs[DFII_PIX_DATA_SIZE * p + offset];
-                            if ptr::read_volatile(addr) as u8 != data {
-                                working = false;
+                    for _ in 0..64 {
+                        sdram_phy::command_prd(DFII_COMMAND_CAS|DFII_COMMAND_CS|
+                                               DFII_COMMAND_RDDATA);
+                        spin_cycles(15);
+
+                        for p in 0..DFII_NPHASES {
+                            for &offset in [n, n + DQS_SIGNAL_COUNT].iter() {
+                                let addr = DFII_PIX_RDDATA_ADDR[p].offset(offset as isize);
+                                let data = prs[DFII_PIX_DATA_SIZE * p + offset];
+                                if ptr::read_volatile(addr) as u8 != data {
+                                    working = false;
+                                }
                             }
                         }
                     }