3 files changed, 11 insertions, 4 deletions

diff --git a/firmware/drivers/ata_mmc.c b/firmware/drivers/ata_mmc.c
index f927a1bdeb..897f59b8be 100644
--- a/firmware/drivers/ata_mmc.c
+++ b/firmware/drivers/ata_mmc.c
@@ -141,10 +141,12 @@ static void mmc_tick(void);
 
 void mmc_select_clock(int card_no)
 {
-    if (card_no == 0)             /* internal */
-        or_b(0x10, &PADRH);       /* set clock gate PA12  CHECKME: mask? */
-    else                          /* external */
-        and_b(~0x10, &PADRH);     /* clear clock gate PA12  CHECKME: mask?*/
+    /* set clock gate for external card / reset for internal card if the
+     * MMC clock polarity bit is 0, vice versa if it is 1 */
+    if ((card_no != 0) ^ (read_hw_mask() & MMC_CLOCK_POLARITY))
+        or_b(0x10, &PADRH);       /* set clock gate PA12 */
+    else
+        and_b(~0x10, &PADRH);     /* clear clock gate PA12 */
 }
 
 static int select_card(int card_no)
diff --git a/firmware/export/hwcompat.h b/firmware/export/hwcompat.h
index 66f29f8b16..01e26df6e0 100644
--- a/firmware/export/hwcompat.h
+++ b/firmware/export/hwcompat.h
@@ -27,6 +27,7 @@
 #define USB_ACTIVE_HIGH 0x0100
 #define PR_ACTIVE_HIGH  0x0100
 #define LCD_CONTRAST_BIAS 0x0200
+#define MMC_CLOCK_POLARITY 0x0400
 #define TUNER_MODEL 0x0800
 
 int read_rom_version(void);
diff --git a/firmware/usb.c b/firmware/usb.c
index 181b1ead1a..e27c003154 100644
--- a/firmware/usb.c
+++ b/firmware/usb.c
@@ -89,11 +89,15 @@ static void usb_enable(bool on)
 #ifdef HAVE_MMC
         mmc_select_clock(mmc_detect() ? 1 : 0);
 #endif
+        if (!(read_hw_mask() & MMC_CLOCK_POLARITY))
+            and_b(~0x20, &PBDRH); /* old circuit needs SCK1 = low while on USB */
         or_b(0x20, &PADRL); /* enable USB */
         and_b(~0x08, &PADRL); /* assert card detect */
     }
     else
     {
+        if (!(read_hw_mask() & MMC_CLOCK_POLARITY))
+            or_b(0x20, &PBDRH); /* reset SCK1 = high for old circuit */
         and_b(~0x20, &PADRL); /* disable USB */
         or_b(0x08, &PADRL); /* deassert card detect */
     }