imx233: implement emi frequency scaling (disabled by default)

CPU frequency scaling is basically useless without scaling the
memory frequency. On the i.MX233, the EMI (external memory
interface) and DRAM blocks are responsable for the DDR settings.
This commits implements emi frequency scaling. Only some settings
are implemented and the timings values only apply to mDDR
(extracted from Sigmatel linux port) and have been checked to
work on the Fuze+ and Zen X-Fi2/3. This feature is still disabled
by default but I expected some battery life savings by boosting
higher to 454MHz and unboosting lower to 64MHz.
Note that changing the emi frequency is particularly tricky and
to avoid writing it entirely in assembly we rely on the compiler
to not use the stack except in the prolog and epilog (because
it's in dram which is disabled when doing the change) and to put
constant pools in iram which should always be true if the
compiler isn't completely dumb and since the code itself is put
in iram. If this proves to be insufficient, one can always switch
the stack to the irq stack since interrupts are disabled during
the change.

Change-Id: If6ef5357f7ff091130ca1063e48536c6028f23ba

5 files changed, 489 insertions, 9 deletions

diff --git a/firmware/target/arm/imx233/clkctrl-imx233.h b/firmware/target/arm/imx233/clkctrl-imx233.h
index 665674108c..30c1c54545 100644
--- a/firmware/target/arm/imx233/clkctrl-imx233.h
+++ b/firmware/target/arm/imx233/clkctrl-imx233.h
@@ -81,6 +81,7 @@
 #define HW_CLKCTRL_EMI__DIV_XTAL_BP 8
 #define HW_CLKCTRL_EMI__DIV_XTAL_BM (0xf << 8)
 #define HW_CLKCTRL_EMI__BUSY_REF_EMI    (1 << 28)
+#define HW_CLKCTRL_EMI__BUSY_REF_XTAL   (1 << 29)
 #define HW_CLKCTRL_EMI__SYNC_MODE_EN    (1 << 30)
 #define HW_CLKCTRL_EMI__CLKGATE     (1 << 31)
 
diff --git a/firmware/target/arm/imx233/emi-imx233.c b/firmware/target/arm/imx233/emi-imx233.c
new file mode 100644
index 0000000000..b10d08134d
--- /dev/null
+++ b/firmware/target/arm/imx233/emi-imx233.c
@@ -0,0 +1,186 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2013 by Amaury Pouly
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#include "emi-imx233.h"
+#include "clkctrl-imx233.h"
+
+struct emi_reg_t
+{
+    int index;
+    uint32_t value;
+};
+
+/* hardcode all the register values for the different settings. This is ugly
+ * but I don't understand what they mean and it's faster this way so...
+ * Recall that everything should be put in iram !
+ * Make sure the last value is written to register 40. */
+
+/* Values extracted from Sigmatel linux port (GPL) */
+
+/** mDDR value */
+static struct emi_reg_t settings_24M[15] ICONST_ATTR =
+{
+    {4, 0x01000101}, {7, 0x01000101}, {12, 0x02010002}, {13, 0x06060a02},
+    {15, 0x01030000}, {17, 0x2d000102}, {18, 0x20200000}, {19, 0x027f1414},
+    {20, 0x01021608}, {21, 0x00000002}, {26, 0x000000b3}, {32, 0x00030687},
+    {33, 0x00000003}, {34, 0x000012c1}, {40, 0x00010000}
+};
+
+static struct emi_reg_t settings_48M[15] ICONST_ATTR =
+{
+    {4, 0x01000101}, {7, 0x01000101}, {13, 0x06060a02}, {12, 0x02010002},
+    {15, 0x02040000}, {17, 0x2d000104}, {18, 0x1f1f0000}, {19, 0x027f0a0a},
+    {20, 0x01021608}, {21, 0x00000004}, {26, 0x0000016f}, {32, 0x00060d17},
+    {33, 0x00000006}, {34, 0x00002582}, {40, 0x00020000}
+};
+
+static struct emi_reg_t settings_60M[15] ICONST_ATTR =
+{
+    {4, 0x01000101}, {7, 0x01000101}, {12, 0x02020002}, {13, 0x06060a02},
+    {15, 0x02040000}, {17, 0x2d000005}, {18, 0x1f1f0000}, {19, 0x027f0a0a},
+    {20, 0x02040a10}, {21, 0x00000006}, {26, 0x000001cc}, {32, 0x00081060},
+    {33, 0x00000008}, {34, 0x00002ee5}, {40, 0x00020000}
+};
+
+static struct emi_reg_t settings_80M[15] ICONST_ATTR __attribute__((alias("settings_60M")));
+
+static struct emi_reg_t settings_96M[15] ICONST_ATTR =
+{
+    {4, 0x00000101}, {7, 0x01000001}, {12, 0x02020002}, {13, 0x06070a02},
+    {15, 0x03050000}, {17, 0x2d000808}, {18, 0x1f1f0000}, {19, 0x020c1010},
+    {20, 0x0305101c}, {21, 0x00000007}, {26, 0x000002e6}, {32, 0x000c1a3b},
+    {33, 0x0000000c}, {34, 0x00004b0d}, {40, 0x00030000}
+};
+
+static struct emi_reg_t settings_120M[15] ICONST_ATTR =
+{
+    {4, 0x00000101}, {7, 0x01000001}, {12, 0x02020002}, {13, 0x06070a02},
+    {15, 0x03050000}, {17, 0x2300080a}, {18, 0x1f1f0000}, {19, 0x020c1010},
+    {20, 0x0306101c}, {21, 0x00000009}, {26, 0x000003a1}, {32, 0x000f20ca},
+    {33, 0x0000000f}, {34, 0x00005dca}, {40, 0x00040000}
+};
+
+static struct emi_reg_t settings_133M[15] ICONST_ATTR =
+{
+    {4, 0x00000101}, {7, 0x01000001}, {12, 0x02020002}, {13, 0x06070a02},
+    {15, 0x03050000}, {17, 0x2000080a}, {18, 0x1f1f0000}, {19, 0x020c1010},
+    {20, 0x0306101c}, {21, 0x0000000a}, {26, 0x00000408}, {32, 0x0010245f},
+    {33, 0x00000010}, {34, 0x00006808}, {40, 0x00040000}
+};
+
+static struct emi_reg_t settings_155M[15] ICONST_ATTR __attribute__((alias("settings_133M")));
+
+static void set_frequency(unsigned long freq) ICODE_ATTR;
+
+static void set_frequency(unsigned long freq)
+{
+    /* Set divider and clear clkgate. Do byte access to register to avoid bothering
+     * with other PFDs */
+    switch(freq)
+    {
+        case IMX233_EMIFREQ_151_MHz:
+            /* clk_emi@ref_emi/3*18/19 */
+            HW_CLKCTRL_FRAC_EMI = 19;
+            __FIELD_SET(HW_CLKCTRL_EMI, DIV_EMI, 3);
+            /* ref_emi@480 MHz
+             * clk_emi@151.58 MHz */
+            break;
+        case IMX233_EMIFREQ_130_MHz:
+            /* clk_emi@ref_emi/2*18/33 */
+            HW_CLKCTRL_FRAC_EMI = 33;
+            __FIELD_SET(HW_CLKCTRL_EMI, DIV_EMI, 2);
+            /* ref_emi@480 MHz
+             * clk_emi@130.91 MHz */
+            break;
+        case IMX233_EMIFREQ_64_MHz:
+        default:
+            /* clk_emi@ref_emi/5*18/27 */
+            HW_CLKCTRL_FRAC_EMI = 27;
+            __FIELD_SET(HW_CLKCTRL_EMI, DIV_EMI, 5);
+            /* ref_emi@480 MHz
+             * clk_emi@64 MHz */
+            break;
+    }
+}
+
+void imx233_emi_set_frequency(unsigned long freq) ICODE_ATTR;
+
+void imx233_emi_set_frequency(unsigned long freq)
+{
+    /** FIXME we rely on the compiler to NOT use the stack here because it's
+     * in iram ! If it's not smart enough, one can switch the switch to use
+     * the irq stack since we are running interrupts disable here ! */
+    /** BUG for freq<=24 MHz we must keep bypass mode since we run on xtal
+     * we this setting is unused by our code so ignore this bug for now */
+    /** WARNING DANGER
+     * Changing the EMI frequency is complicated because it requires to
+     * completely shutdown the external memory interface. We must make sure
+     * that this code and all the data it uses in in iram and that no access to
+     * the sdram will be made during the change. Care must be taken w.r.t to
+     * the cache also. */
+    /** FIXME assume that auto-slow is disabled here since that could put some
+     * clock below the minimum value and we want to spend as less time as
+     * possible in this state anyway. */
+    
+    /* first disable all interrupts */
+    int oldstatus = disable_interrupt_save(IRQ_FIQ_STATUS);
+    /* flush the cache */
+    commit_discard_idcache();
+    /* put DRAM into self-refresh mode */
+    HW_DRAM_CTL08 |= HW_DRAM_CTL08__SREFRESH;
+    /* wait for DRAM to be halted */
+    while(!(HW_EMI_STAT & HW_EMI_STAT__DRAM_HALTED));
+    /* load timings */
+    struct emi_reg_t *regs;
+    if(freq <= 24000) regs = settings_24M;
+    else if(freq <= 48000) regs = settings_48M;
+    else if(freq <= 60000) regs = settings_60M;
+    else if(freq <= 80000) regs = settings_80M;
+    else if(freq <= 96000) regs = settings_96M;
+    else if(freq <= 120000) regs = settings_120M;
+    else if(freq <= 133000) regs = settings_133M;
+    else regs = settings_155M;
+
+    do
+        HW_DRAM_CTLxx(regs->index) = regs->value;
+    while((regs++)->index != 40);
+    /* switch emi to xtal */
+    __REG_SET(HW_CLKCTRL_CLKSEQ) = HW_CLKCTRL_CLKSEQ__BYPASS_EMI;
+    /* wait for transition */
+    while(HW_CLKCTRL_EMI & HW_CLKCTRL_EMI__BUSY_REF_XTAL);
+    /* put emi dll into reset mode */
+    __REG_SET(HW_EMI_CTRL) = HW_EMI_CTRL__DLL_RESET | HW_EMI_CTRL__DLL_SHIFT_RESET;
+    /* load the new frequency dividers */
+    set_frequency(freq);
+    /* switch emi back to pll */
+    __REG_CLR(HW_CLKCTRL_CLKSEQ) = HW_CLKCTRL_CLKSEQ__BYPASS_EMI;
+    /* wait for transition */
+    while(HW_CLKCTRL_EMI & HW_CLKCTRL_EMI__BUSY_REF_EMI);
+    /* allow emi dll to lock again */
+    __REG_CLR(HW_EMI_CTRL) = HW_EMI_CTRL__DLL_RESET | HW_EMI_CTRL__DLL_SHIFT_RESET;
+    /* wait for lock */
+    while(!(HW_DRAM_CTL04 & HW_DRAM_CTL04__DLLLOCKREG));
+    /* get DRAM out of self-refresh mode */
+    HW_DRAM_CTL08 &= ~HW_DRAM_CTL08__SREFRESH;
+    /* wait for DRAM to be to run again */
+    while(HW_EMI_STAT & HW_EMI_STAT__DRAM_HALTED);
+
+    restore_interrupt(oldstatus);
+}
diff --git a/firmware/target/arm/imx233/emi-imx233.h b/firmware/target/arm/imx233/emi-imx233.h
new file mode 100644
index 0000000000..8106d27dfe
--- /dev/null
+++ b/firmware/target/arm/imx233/emi-imx233.h
@@ -0,0 +1,260 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2013 by Amaury Pouly
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#ifndef __EMI_IMX233_H__
+#define __EMI_IMX233_H__
+
+#include "cpu.h"
+#include "system.h"
+#include "system-target.h"
+
+#define HW_EMI_BASE     0x80020000
+
+#define HW_EMI_CTRL     (*(volatile uint32_t *)(HW_EMI_BASE + 0x0))
+#define HW_EMI_CTRL__DLL_SHIFT_RESET    (1 << 25)
+#define HW_EMI_CTRL__DLL_RESET          (1 << 24)
+
+/* this register is undocumented but exists, I put the whole doc here */
+#define HW_EMI_STAT     (*(volatile uint32_t *)(HW_EMI_BASE + 0x10))
+#define HW_EMI_STAT__DRAM_PRESENT       (1 << 31)
+#define HW_EMI_STAT__NOR_PRESENT        (1 << 30)
+#define HW_EMI_STAT__LARGE_DRAM_ENABLED (1 << 29)
+#define HW_EMI_STAT__DRAM_HALTED        (1 << 1)
+#define HW_EMI_STAT__NOR_BUSY           (1 << 0)
+
+/* another undocumented registers (there are some more) */
+#define HW_EMI_TIME     (*(volatile uint32_t *)(HW_EMI_BASE + 0x20))
+#define HW_EMI_TIME__THZ_BP     24
+#define HW_EMI_TIME__THZ_BM     (0xf << 24)
+#define HW_EMI_TIME__TDH_BP     16
+#define HW_EMI_TIME__TDH_BM     (0xf << 16)
+#define HW_EMI_TIME__TDS_BP     8
+#define HW_EMI_TIME__TDS_BM     (0x1f << 8)
+#define HW_EMI_TIME__TAS_BP     0
+#define HW_EMI_TIME__TAS_BM     (0xf << 0)
+
+/** WARNING: the HW_DRAM_* registers don't have a SCT variant ! */
+#define HW_DRAM_BASE    0x800E0000
+
+#define HW_DRAM_CTLxx(xx) (*(volatile uint32_t *)(HW_DRAM_BASE + 0x4 * (xx)))
+
+#define HW_DRAM_CTL00   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x0))
+#define HW_DRAM_CTL01   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x4))
+#define HW_DRAM_CTL02   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x8))
+#define HW_DRAM_CTL03   (*(volatile uint32_t *)(HW_DRAM_BASE + 0xc))
+
+#define HW_DRAM_CTL04   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x10))
+#define HW_DRAM_CTL04__DLL_BYPASS_MODE  (1 << 24)
+#define HW_DRAM_CTL04__DLLLOCKREG       (1 << 16)
+
+#define HW_DRAM_CTL05   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x14))
+#define HW_DRAM_CTL05__EN_LOWPOWER_MODE (1 << 0)
+
+#define HW_DRAM_CTL06   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x18))
+#define HW_DRAM_CTL07   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x1c))
+
+#define HW_DRAM_CTL08   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x20))
+#define HW_DRAM_CTL08__SREFRESH (1 << 8)
+
+#define HW_DRAM_CTL09   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x24))
+
+#define HW_DRAM_CTL10   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x28))
+#define HW_DRAM_CTL10__TEMRS_BP 8
+#define HW_DRAM_CTL10__TEMRS_BM (0x3 << 8)
+
+#define HW_DRAM_CTL11   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x2c))
+#define HW_DRAM_CTL11__CASLAT_BP    0
+#define HW_DRAM_CTL11__CASLAT_BM    (0x7 << 0)
+
+#define HW_DRAM_CTL12   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x30))
+#define HW_DRAM_CTL12__TCKE_BP      0
+#define HW_DRAM_CTL12__TCKE_BM      (0x7 << 0)
+#define HW_DRAM_CTL12__TRRD_BP      16
+#define HW_DRAM_CTL12__TRRD_BM      (0x7 << 16)
+#define HW_DRAM_CTL12__TWR_INT_BP   24
+#define HW_DRAM_CTL12__TWR_INT_BM   (0x7 << 24)
+
+#define HW_DRAM_CTL13   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x34))
+#define HW_DRAM_CTL13__TWTR_BP      0
+#define HW_DRAM_CTL13__TWTR_BM      (0x7 << 0)
+#define HW_DRAM_CTL13__CASLAT_LIN_BP    16
+#define HW_DRAM_CTL13__CASLAT_LIN_BM    (0xf << 16)
+#define HW_DRAM_CTL13__CASLAT_LIN_GATE_BP   24
+#define HW_DRAM_CTL13__CASLAT_LIN_GATE_BM   (0xf << 24)
+
+#define HW_DRAM_CTL14   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x38))
+
+#define HW_DRAM_CTL15   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x3c))
+#define HW_DRAM_CTL15__TDAL_BP      16
+#define HW_DRAM_CTL15__TDAL_BM      (0xf << 16)
+#define HW_DRAM_CTL15__TRP_BP       24
+#define HW_DRAM_CTL15__TRP_BM       (0xf << 24)
+
+#define HW_DRAM_CTL16   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x40))
+#define HW_DRAM_CTL16__TMRD_BP       24
+#define HW_DRAM_CTL16__TMRD_BM       (0x1f << 24)
+
+#define HW_DRAM_CTL17   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x44))
+#define HW_DRAM_CTL17__TRC_BP        0
+#define HW_DRAM_CTL17__TRC_BM        (0x1f << 0)
+#define HW_DRAM_CTL17__DLL_INCREMENT_BP     8
+#define HW_DRAM_CTL17__DLL_INCREMENT_BM     (0xff << 0)
+#define HW_DRAM_CTL17__DLL_START_POINT_BP   24
+#define HW_DRAM_CTL17__DLL_START_POINT_BM   (0xff << 24)
+
+#define HW_DRAM_CTL18   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x48))
+#define HW_DRAM_CTL17__DLL_DQS_DELAY_0_BP   16
+#define HW_DRAM_CTL17__DLL_DQS_DELAY_0_BM   (0x7f << 16)
+#define HW_DRAM_CTL17__DLL_DQS_DELAY_1_BP   24
+#define HW_DRAM_CTL17__DLL_DQS_DELAY_1_BM   (0x7f << 24)
+
+#define HW_DRAM_CTL19   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x4c))
+#define HW_DRAM_CTL19__DQS_OUT_SHIFT_BP     16
+#define HW_DRAM_CTL19__DQS_OUT_SHIFT_BM     (0x7f << 16)
+
+#define HW_DRAM_CTL20   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x50))
+#define HW_DRAM_CTL20__WR_DQS_SHIFT_BP  0
+#define HW_DRAM_CTL20__WR_DQS_SHIFT_BM  (0x7f << 0)
+#define HW_DRAM_CTL20__TRAS_MIN_BP      16
+#define HW_DRAM_CTL20__TRAS_MIN_BM      (0xff << 16)
+#define HW_DRAM_CTL20__TRCD_INT_BP      24
+#define HW_DRAM_CTL20__TRCD_INT_BM      (0xff << 24)
+
+#define HW_DRAM_CTL21   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x54))
+#define HW_DRAM_CTL21__TRFC_BP      0
+#define HW_DRAM_CTL21__TRFC_BM      (0xff << 0)
+
+#define HW_DRAM_CTL22   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x58))
+#define HW_DRAM_CTL23   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x5c))
+#define HW_DRAM_CTL24   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x60))
+#define HW_DRAM_CTL25   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x64))
+
+#define HW_DRAM_CTL26   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x68))
+#define HW_DRAM_CTL26__TREF_BP      0
+#define HW_DRAM_CTL26__TREF_BM      (0xfff << 0)
+
+#define HW_DRAM_CTL27   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x6c))
+#define HW_DRAM_CTL28   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x70))
+#define HW_DRAM_CTL29   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x74))
+#define HW_DRAM_CTL30   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x78))
+
+#define HW_DRAM_CTL31   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x7c))
+#define HW_DRAM_CTL31__TDLL_BP      16
+#define HW_DRAM_CTL31__TDLL_BM      (0xffff << 16)
+
+#define HW_DRAM_CTL32   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x80))
+#define HW_DRAM_CTL32__TRAS_MAX_BP  0
+#define HW_DRAM_CTL32__TRAS_MAX_BM  (0xffff << 0)
+#define HW_DRAM_CTL32__TXSNR_BP     16
+#define HW_DRAM_CTL32__TXSNR_BM     (0xffff << 16)
+
+#define HW_DRAM_CTL33   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x84))
+#define HW_DRAM_CTL33__TXSR_BP      0
+#define HW_DRAM_CTL33__TXSR_BM      (0xffff << 0)
+
+#define HW_DRAM_CTL34   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x88))
+#define HW_DRAM_CTL34__TINIT_BP 0
+#define HW_DRAM_CTL34__TINIT_BM 0xffffff
+
+#define HW_DRAM_CTL35   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x8c))
+#define HW_DRAM_CTL36   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x90))
+#define HW_DRAM_CTL37   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x94))
+#define HW_DRAM_CTL38   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x98))
+#define HW_DRAM_CTL39   (*(volatile uint32_t *)(HW_DRAM_BASE + 0x9a))
+
+#define HW_DRAM_CTL40   (*(volatile uint32_t *)(HW_DRAM_BASE + 0xa0))
+#define HW_DRAM_CTL40__TPDEX_BP     16
+#define HW_DRAM_CTL40__TPDEX_BM     (0xffff << 16)
+
+/** Interesting fields:
+ * - TCKE: CTL12
+ * - TDAL: CTL15
+ * - TDLL: CTL31
+ * - TEMRS: CTL10
+ * - TINIT: CTL34
+ * - TMRD: CTL16
+ * - TPDEX: CTL40
+ * - TRAS_MAX: CTL32
+ * - TRAS_MIN: CTL20
+ * - TRC: CTL17
+ * - TRCD_INT: CTL20
+ * - TREF: CTL26
+ * - TRFC: CTL21
+ * - TRP: CTL15
+ * - TRRD: CTL12
+ * - TWR_INT: CTL12
+ * - TWTR: CTL13
+ * - TXSNR: CTL32
+ * - TXSR: CTL33
+ * - DLL_DQS_DELAY_BYPASS_0
+ * - DLL_DQS_DELAY_BYPASS_1
+ * - DQS_OUT_SHIFT_BYPASS
+ * - WR_DQS_SHIFT_BYPASS
+ * - DLL_INCREMENT: CTL17
+ * - DLL_START_POINT: CTL17
+ * - DLL_DQS_DELAY_0: CTL18
+ * - DLL_DQS_DELAY_1: CTL18
+ * - DQS_OUT_SHIFT: CTL19
+ * - WR_DQS_SHIFT: CTL20
+ * - CAS: CTL11
+ * - DLL_BYPASS_MODE: CTL04
+ * - SREFRESH: CTL08
+ * - CASLAT_LIN: CTL13
+ * - CASLAT_LIN_GATE: CTL13
+ *
+ * Interesting registers:
+ * - CTL04: DLL_BYPASS_MODE
+ * - CTL08: SREFRESH
+ * - CTL10: TEMRS
+ * - CTL11: CASLAT
+ * - CTL12: TCKE TRRD TWR_INT
+ * - CTL13: TWTR CASLAT_LIN CASLAT_LIN_GATE
+ * - CTL15: TDAL TRP
+ * - CTL16: TMRD
+ * - CTL17: TRC DLL_INCREMENT DLL_START_POINT
+ * - CTL18: DLL_DQS_DELAY_0 DLL_DQS_DELAY_1
+ * - CTL19: DQS_OUT_SHIFT
+ * - CTL20: WR_DQS_SHIFT TRAS_MIN TRCD_INT
+ * - CTL21 TRFC
+ * - CTL26: TREF
+ * - CTL31: TDLL
+ * - CTL32: TRAS_MAX TXSNR TXSR: CTL33
+ * - CTL34: TINIT
+ * - CTL40: TPDEX
+
+ * - DLL_DQS_DELAY_BYPASS_0
+ * - DLL_DQS_DELAY_BYPASS_1
+ * - DQS_OUT_SHIFT_BYPASS
+ * - WR_DQS_SHIFT_BYPASS
+ */
+
+/**
+ * Absolute maximum EMI speed:  151.58 MHz (mDDR),  130.91 MHz (DDR)
+ * Intermediate EMI speeds: 130.91 MHz,  120.00 MHz, 64 MHz, 24 MHz
+ * Absolute minimum CPU speed: 24 MHz */
+#define IMX233_EMIFREQ_151_MHz  151580
+#define IMX233_EMIFREQ_130_MHz  130910
+#define IMX233_EMIFREQ_120_MHz  120000
+#define IMX233_EMIFREQ_64_MHz    64000
+#define IMX233_EMIFREQ_24_MHz    24000
+
+void imx233_emi_set_frequency(unsigned long freq);
+
+#endif /* __EMI_IMX233_H__ */
diff --git a/firmware/target/arm/imx233/system-imx233.c b/firmware/target/arm/imx233/system-imx233.c
index 07ab62d680..68f063512d 100644
--- a/firmware/target/arm/imx233/system-imx233.c
+++ b/firmware/target/arm/imx233/system-imx233.c
@@ -36,6 +36,7 @@
 #include "lradc-imx233.h"
 #include "rtc-imx233.h"
 #include "power-imx233.h"
+#include "emi-imx233.h"
 #include "lcd.h"
 #include "backlight-target.h"
 #include "button.h"
@@ -196,6 +197,8 @@ void set_cpu_frequency(long frequency)
             imx233_clkctrl_set_fractional_divisor(CLK_CPU, 19);
             imx233_clkctrl_set_clock_divisor(CLK_CPU, 1);
             imx233_clkctrl_set_bypass_pll(CLK_CPU, false);
+
+            imx233_emi_set_frequency(IMX233_EMIFREQ_130_MHz);
             /* ref_cpu@480 MHz
              * ref_emi@480 MHz
              * clk_emi@130.91 MHz
@@ -211,12 +214,30 @@ void set_cpu_frequency(long frequency)
             imx233_clkctrl_set_fractional_divisor(CLK_CPU, 33);
             imx233_clkctrl_set_clock_divisor(CLK_CPU, 1);
             imx233_clkctrl_set_bypass_pll(CLK_CPU, false);
+
+            imx233_emi_set_frequency(IMX233_EMIFREQ_130_MHz);
             /* ref_cpu@480 MHz
              * ref_emi@480 MHz
              * clk_emi@130.91 MHz
              * clk_p@261.82 MHz
              * clk_h@130.91 MHz */
             break;
+        case IMX233_CPUFREQ_64_MHz:
+            /* set VDDD to 1.050 mV (brownout at 0.975 mV) */
+            imx233_power_set_regulator(REGULATOR_VDDD, 1050, 975);
+            /* clk_h@clk_p */
+            imx233_clkctrl_set_clock_divisor(CLK_HBUS, 1);
+            /* clk_p@ref_cpu/5*18/27 */
+            imx233_clkctrl_set_fractional_divisor(CLK_CPU, 27);
+            imx233_clkctrl_set_clock_divisor(CLK_CPU, 5);
+            imx233_clkctrl_set_bypass_pll(CLK_CPU, false);
+
+            imx233_emi_set_frequency(IMX233_EMIFREQ_64_MHz);
+            /* ref_cpu@480 MHz
+             * ref_emi@480 MHz
+             * clk_emi@64 MHz
+             * clk_p@64 MHz
+             * clk_h@64 MHz */
         default:
             break;
     }
diff --git a/firmware/target/arm/imx233/system-target.h b/firmware/target/arm/imx233/system-target.h
index 5515597570..c6073a9ae3 100644
--- a/firmware/target/arm/imx233/system-target.h
+++ b/firmware/target/arm/imx233/system-target.h
@@ -37,6 +37,18 @@
 
 #define HW_DIGCTL_MICROSECONDS  (*(volatile uint32_t *)(HW_DIGCTL_BASE + 0xC0))
 
+#define HW_DIGCTL_ARMCACHE      (*(volatile uint32_t *)(HW_DIGCTL_BASE + 0x2b0))
+#define HW_DIGCTL_ARMCACHE__ITAG_SS_BP  0
+#define HW_DIGCTL_ARMCACHE__ITAG_SS_BM  (3 << 0)
+#define HW_DIGCTL_ARMCACHE__DTAG_SS_BP  4
+#define HW_DIGCTL_ARMCACHE__DTAG_SS_BM  (3 << 4)
+#define HW_DIGCTL_ARMCACHE__CACHE_SS_BP  8
+#define HW_DIGCTL_ARMCACHE__CACHE_SS_BM  (3 << 8)
+#define HW_DIGCTL_ARMCACHE__DRTY_SS_BP  12
+#define HW_DIGCTL_ARMCACHE__DRTY_SS_BM  (3 << 12)
+#define HW_DIGCTL_ARMCACHE__VALID_SS_BP  16
+#define HW_DIGCTL_ARMCACHE__VALID_SS_BM  (3 << 16)
+
 /* USB Phy */
 #define HW_USBPHY_BASE          0x8007C000 
 #define HW_USBPHY_PWD           (*(volatile uint32_t *)(HW_USBPHY_BASE + 0))
@@ -48,17 +60,17 @@
  * Absolute maximum CPU speed: 454.74 MHz
  * Intermediate CPU speeds: 392.73 MHz, 360MHz, 261.82 MHz, 64 MHz
  * Absolute minimum CPU speed: 24 MHz */
-#define IMX233_CPUFREQ_454_MHz  454740000
-#define IMX233_CPUFREQ_392_MHz  392730000
-#define IMX233_CPUFREQ_360_MHz  360000000
-#define IMX233_CPUFREQ_261_MHz  261820000
-#define IMX233_CPUFREQ_64_MHz    64000000
-#define IMX233_CPUFREQ_24_MHz    24000000
+#define IMX233_CPUFREQ_454_MHz  454740
+#define IMX233_CPUFREQ_392_MHz  392730
+#define IMX233_CPUFREQ_360_MHz  360000
+#define IMX233_CPUFREQ_261_MHz  261820
+#define IMX233_CPUFREQ_64_MHz    64000
+#define IMX233_CPUFREQ_24_MHz    24000
 
-#define CPUFREQ_DEFAULT     IMX233_CPUFREQ_261_MHz
-#define CPUFREQ_NORMAL      IMX233_CPUFREQ_261_MHz
+#define CPUFREQ_DEFAULT     IMX233_CPUFREQ_64_MHz
+#define CPUFREQ_NORMAL      IMX233_CPUFREQ_64_MHz
 #define CPUFREQ_MAX         IMX233_CPUFREQ_454_MHz
-#define CPUFREQ_SLEEP       IMX233_CPUFREQ_261_MHz
+#define CPUFREQ_SLEEP       IMX233_CPUFREQ_64_MHz
 
 void udelay(unsigned us);
 bool imx233_us_elapsed(uint32_t ref, unsigned us_delay);