TQM866M: fix SDRAM refresh
At 133 MHz the current SDRAM refresh rate is too fast
(measured 4 * 1.17 us).
CFG_MAMR_PTA changes from 39 to 97. This result
in a refresh rate of 4 * 7.8 us at the default clock
50 MHz. At 133 MHz the value will be then 4 * 2.9 us.
This is a compromise until a new method is found to
adjust the refresh rate.
Signed-off-by: Martin Krause <martin.krause@tqs.de>
diff --git a/include/configs/TQM866M.h b/include/configs/TQM866M.h
index 76facc4..ca3c166 100644
--- a/include/configs/TQM866M.h
+++ b/include/configs/TQM866M.h
@@ -426,26 +426,30 @@
#define CFG_PTA_PER_CLK ((4096 * 64 * 1000) / (4 * 64))
/*
- * Memory Periodic Timer Prescaler
- * Periodic timer for refresh, start with refresh rate for 40 MHz clock
- * (CFG_8xx_CPUCLK_MIN / CFG_PTA_PER_CLK)
+ * Periodic timer (MAMR[PTx]) for 4 * 7.8 us refresh (= 31.2 us per quad)
+ *
+ * CPUclock(MHz) * 31.2
+ * CFG_MAMR_PTA = ----------------------------------- with DFBRG = 0
+ * 2^(2*SCCR[DFBRG]) * MPTPR_PTP_DIV16
+ *
+ * CPU clock = 15 MHz: CFG_MAMR_PTA = 29 -> 4 * 7.73 us
+ * CPU clock = 50 MHz: CFG_MAMR_PTA = 97 -> 4 * 7.76 us
+ * CPU clock = 66 MHz: CFG_MAMR_PTA = 128 -> 4 * 7.75 us
+ * CPU clock = 133 MHz: CFG_MAMR_PTA = 255 -> 4 * 7.67 us
+ *
+ * Value 97 is for 4 * 7.8 us at 50 MHz. So the refresh cycle requirement will
+ * be met also in the default configuration, i.e. if environment variable
+ * 'cpuclk' is not set.
*/
-#define CFG_MAMR_PTA 39
+#define CFG_MAMR_PTA 97
/*
- * For 16 MBit, refresh rates could be 31.3 us
- * (= 64 ms / 2K = 125 / quad bursts).
- * For a simpler initialization, 15.6 us is used instead.
- *
- * #define CFG_MPTPR_2BK_2K MPTPR_PTP_DIV32 for 2 banks
- * #define CFG_MPTPR_1BK_2K MPTPR_PTP_DIV64 for 1 bank
+ * Memory Periodic Timer Prescaler Register (MPTPR) values.
*/
-#define CFG_MPTPR_2BK_4K MPTPR_PTP_DIV16 /* setting for 2 banks */
-#define CFG_MPTPR_1BK_4K MPTPR_PTP_DIV32 /* setting for 1 bank */
-
-/* refresh rate 7.8 us (= 64 ms / 8K = 31.2 / quad bursts) for 256 MBit */
-#define CFG_MPTPR_2BK_8K MPTPR_PTP_DIV8 /* setting for 2 banks */
-#define CFG_MPTPR_1BK_8K MPTPR_PTP_DIV16 /* setting for 1 bank */
+/* 4 * 7.8 us refresh (= 31.2 us per quad) at 50 MHz and PTA = 97 */
+#define CFG_MPTPR_2BK_4K MPTPR_PTP_DIV16
+/* 4 * 3.9 us refresh (= 15.6 us per quad) at 50 MHz and PTA = 97 */
+#define CFG_MPTPR_2BK_8K MPTPR_PTP_DIV8
/*
* MAMR settings for SDRAM