M:Robe 500/M66591 USB improvements: Interrupts now work, a bug in odd-length transfers has been fixed. Buffers that are not initially short aligned are also now supported. Enable USB HID mouse mode.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@23483 a1c6a512-1295-4272-9138-f99709370657

6 files changed, 193 insertions, 80 deletions

diff --git a/apps/keymaps/keymap-touchscreen.c b/apps/keymaps/keymap-touchscreen.c
index 74673cc..e7cf87a 100644
--- a/apps/keymaps/keymap-touchscreen.c
+++ b/apps/keymaps/keymap-touchscreen.c
@@ -310,6 +310,27 @@ static const struct button_mapping button_context_usb_hid_mode_browser[] = {
 
     LAST_ITEM_IN_LIST__NEXTLIST(CONTEXT_USB_HID)
 }; /* button_context_usb_hid_mode_browser */
+
+#ifdef HAVE_USB_HID_MOUSE
+static const struct button_mapping button_context_usb_hid_mode_mouse[] = {
+    { ACTION_USB_HID_MOUSE_UP,                BUTTON_TOPMIDDLE,                 BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_UP_REP,            BUTTON_TOPMIDDLE|BUTTON_REPEAT,   BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_DOWN,              BUTTON_BOTTOMMIDDLE,              BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_DOWN_REP,          BUTTON_BOTTOMMIDDLE|BUTTON_REPEAT,BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_LEFT,              BUTTON_MIDLEFT,                   BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_LEFT_REP,          BUTTON_MIDLEFT|BUTTON_REPEAT,     BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_RIGHT,             BUTTON_MIDRIGHT,                  BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_RIGHT_REP,         BUTTON_MIDRIGHT|BUTTON_REPEAT,    BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_BUTTON_LEFT,       BUTTON_CENTER,                    BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_BUTTON_LEFT_REL,   BUTTON_CENTER|BUTTON_REL,         BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_WHEEL_SCROLL_UP,   BUTTON_TOPRIGHT,                  BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_WHEEL_SCROLL_UP,   BUTTON_TOPRIGHT|BUTTON_REPEAT,    BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_WHEEL_SCROLL_DOWN, BUTTON_BOTTOMRIGHT,               BUTTON_NONE },
+    { ACTION_USB_HID_MOUSE_WHEEL_SCROLL_DOWN, BUTTON_BOTTOMRIGHT|BUTTON_REPEAT, BUTTON_NONE },
+
+    LAST_ITEM_IN_LIST__NEXTLIST(CONTEXT_USB_HID)
+}; /* button_context_usb_hid_mode_mouse */
+#endif
 #endif
 
 const struct button_mapping* get_context_mapping(int context)
@@ -373,8 +394,13 @@ const struct button_mapping* get_context_mapping(int context)
             return button_context_usb_hid_mode_presentation;
         case CONTEXT_USB_HID_MODE_BROWSER:
             return button_context_usb_hid_mode_browser;
+#ifdef HAVE_USB_HID_MOUSE
+        case CONTEXT_USB_HID_MODE_MOUSE:
+            return button_context_usb_hid_mode_mouse;
 #endif
-
+#endif
+        default:
+            return button_context_standard;
     }
     return button_context_standard;
 }
diff --git a/firmware/drivers/m66591.c b/firmware/drivers/m66591.c
index 2ce121a..1197485 100644
--- a/firmware/drivers/m66591.c
+++ b/firmware/drivers/m66591.c
@@ -19,7 +19,7 @@
  * KIND, either express or implied.
  *
  ****************************************************************************/
-#define LOGF_ENABLE
+//#define LOGF_ENABLE
 
 #include "system.h"
 #include "config.h"
@@ -47,9 +47,10 @@
  */
 #define HISPEED
 
-/* Right now sending blocks till the full transfer has completed, this needs to
- *  be fixed so that it does not require a block. (USB_TRAN_LOCK ideally would
- *  not be set).
+/* Right now sending blocks till the full transfer has completed. The driver
+ *  will work without USB_TRAN_BLOCK set, but it is more than 50% slower.  
+ *  The driver is more "Proper" without USB_TRAN_BLOCK defined so if you start
+ *  having freezeups or trouble using USB undefine this option.
  */
 #define USB_TRAN_BLOCK
 
@@ -69,7 +70,8 @@ static int pipe_maxpack_size (int pipe);
 static void control_received(void);
 static void transfer_complete(int endpoint);
 static int mxx_transmit_receive(int endpoint);
-static int mxx_queue(int endpoint, void * ptr, int length, bool send);
+static int mxx_queue(int endpoint, void * ptr, int length, bool send, 
+    bool wait);
 
 struct M66591_epstat {
     unsigned char dir;      /* endpoint direction */
@@ -91,6 +93,15 @@ static volatile unsigned short * pipe_ctrl_addr(int pipe) {
     }
 }
 
+static void pipe_init(int pipe) {
+    volatile unsigned short *pipe_cfg;
+    pipe_cfg = pipe_ctrl_addr(pipe);
+    
+    *pipe_cfg |= 1<<9;      /* ACLR */
+    *pipe_cfg &= ~(1<<9);   /* Force de-assertion */
+    *pipe_cfg |= 1<<8;      /* SQCLR */
+}
+
 /* This function sets the pipe/endpoint handshake */
 static void pipe_handshake(int pipe, int handshake) {
     handshake&=0x03;
@@ -125,7 +136,10 @@ static int pipe_buffer_size (int pipe) {
         return 256;
     case 1:
     case 2:
-        return 1024;
+        if(M66591_PIPE_CFGWND & (1<<9) )
+            return 1024;
+        else
+            return 512;
     case 3:
     case 4:
         return 512;
@@ -206,7 +220,7 @@ static void transfer_complete(int endpoint) {
     logf("mxx: ep %d transfer complete", endpoint);
     int temp=M66591_eps[endpoint].dir ? USB_DIR_IN : USB_DIR_OUT;
     usb_core_transfer_complete(endpoint, temp, 0, 
-        M66591_eps[endpoint].length);
+        M66591_eps[endpoint].count);
 }
 
 /* This is the main transmit routine that is typically called from the interrupt
@@ -250,7 +264,8 @@ static int mxx_transmit_receive(int endpoint) {
         length = M66591_eps[endpoint].length;
 #else
         int bufsize=pipe_buffer_size(endpoint);
-        length=MIN(M66591_eps[endpoint].length, bufsize);
+        length=MIN(M66591_eps[endpoint].length - M66591_eps[endpoint].count, 
+            bufsize);
 #endif
 
         /* Calculate the position in the buffer, all transfers should be 2-byte
@@ -259,32 +274,70 @@ static int mxx_transmit_receive(int endpoint) {
         ptrs = (unsigned short *)(M66591_eps[endpoint].buf
             + M66591_eps[endpoint].count);
         
-        /* Start sending data in 16-bit words */
-        for (i = 0; i < (length>>1); i++) { 
-            /* This wait is dangerous in the event that something happens to 
-             *  the PHY pipe where it never becomes ready again, should probably
-             *  add a timeout, and ideally completely remove.
-             */
-            while(!(M66591_CPORT_CTRL1&(1<<13))){};
+        /* Check if the buffer is alligned */
+        if( LIKELY(((int)ptrs) & 0x01) == 0 )
+        {
+            /* Start sending data in 16-bit words (fast) */
+            for (i = 0; i < (length>>1); i++) { 
+#if defined(USB_TRAN_BLOCK)
+                /* This wait is dangerous in the event that something happens 
+                 *  to the PHY pipe where it never becomes ready again, should 
+                 *  probably add a timeout, and ideally completely remove.
+                 */
+                while(!(M66591_CPORT_CTRL1&(1<<13))){};
+#endif
 
-            M66591_CPORT = *ptrs++;
-            M66591_eps[endpoint].count+=2;
-        }
-        
-        /* If the length is odd, send the last byte after setting the byte width
-         *  of the FIFO.
-         */
-        if(length & 0x01) {
-            /* Unset MBW (8-bit transfer) */
-            M66591_CPORT_CTRL0 &= ~(1<<10);
-            M66591_CPORT = *((unsigned char *)ptrs - 1);
-            M66591_eps[endpoint].count++;
+                M66591_CPORT = *ptrs++;
+                M66591_eps[endpoint].count+=2;
+            }
+            
+            /* If the length is odd, send the last byte after setting the byte 
+             *  width of the FIFO.
+             */
+            if(length & 0x01) {
+                /* Unset MBW (8-bit transfer) */
+                M66591_CPORT_CTRL0 &= ~(1<<10);
+                M66591_CPORT = *((unsigned char *)ptrs);
+                M66591_eps[endpoint].count++;
+            }
         }
-        
-        /* Set BVAL if length is not a multiple of the maximum packet size */
-        if( (length == 0) || (length % maxpack != 0) ) {
-            logf("mxx: do set BVAL");
-            M66591_CPORT_CTRL1 |= (1<<15);
+        else
+        {
+            /* The buffer is mis-aligned - data needs to be organized first. 
+             *  This is slower than the above method.
+             */
+            unsigned short sbuf;
+            unsigned char *ptrc = (unsigned char*)ptrs;
+            
+            /* Start sending data in 16-bit words */
+            for (i = 0; i < (length>>1); i++) { 
+#if defined(USB_TRAN_BLOCK)
+                /* This wait is dangerous in the event that something happens 
+                 *  to the PHY pipe where it never becomes ready again, should 
+                 *  probably add a timeout, and ideally completely remove.
+                 */
+                while(!(M66591_CPORT_CTRL1&(1<<13))){};
+#endif
+
+                /* These are mis-aligned accesses so the data nees to be
+                 *  arranged.
+                 */
+                sbuf = (*(ptrc+1) << 8) | *ptrc;
+                ptrc += 2;
+
+                M66591_CPORT = sbuf;
+                M66591_eps[endpoint].count+=2;
+            }
+            
+            /* If the length is odd, send the last byte after setting the byte 
+             *  width of the FIFO.
+             */
+            if(length & 0x01) {
+                /* Unset MBW (8-bit transfer) */
+                M66591_CPORT_CTRL0 &= ~(1<<10);
+                M66591_CPORT = *ptrc;
+                M66591_eps[endpoint].count++;
+            }
         }
         
         /* If the transfer is complete set up interrupts to notify when FIFO is
@@ -302,6 +355,12 @@ static int mxx_transmit_receive(int endpoint) {
             /* There is still data to transfer, make sure READY is enabled */
             M66591_INTCFG_RDY |= 1 << endpoint;
         }
+        
+        /* Set BVAL if length is not a multiple of the maximum packet size */
+        if( (length == 0) || (length % maxpack != 0) ) {
+            logf("mxx: do set BVAL");
+            M66591_CPORT_CTRL1 |= (1<<15) | ((length == 0) << 14);
+        }
     } else {
         /* Read data from FIFO */
         
@@ -366,8 +425,17 @@ static int mxx_transmit_receive(int endpoint) {
 
 /* This function is used to start transfers.  It is a helper function for the 
  *  usb_drv_send_nonblocking, usb_drv_send, and usb_drv_receive functions.
+ *
+ * The functionality for wait needs to be added.  Currently the driver is 
+ *  always used in a blocking mode(USB_TRAN_BLOCK) so it is not required.
  */
-static int mxx_queue(int endpoint, void * ptr, int length, bool send) {
+static int mxx_queue(int endpoint, void * ptr, int length, bool send, 
+    bool wait) 
+{
+#if defined(USB_TRAN_BLOCK) && !defined(LOGF_ENABLE)
+    (void) wait;
+#endif
+
     /* Disable IRQs */
     int flags = disable_irq_save();
 
@@ -384,7 +452,8 @@ static int mxx_queue(int endpoint, void * ptr, int length, bool send) {
     M66591_eps[endpoint].dir=send;
     M66591_eps[endpoint].waiting=true;
 
-    logf("mxx: queue ep %d %s, len: %d", endpoint, send ? "out" : "in", length);
+    logf("mxx: queue ep %d %s, len: %d, wait: %d", 
+        endpoint, send ? "out" : "in", length, wait);
     
     /* Pick the pipe that communications are happening on */
     pipe_c_select(endpoint, send);
@@ -436,9 +505,10 @@ static int mxx_queue(int endpoint, void * ptr, int length, bool send) {
  * This is the interrupt handler for this driver.  It should be called from the
  *  target interrupt handler routine (eg. GPIO3 on M:Robe 500).
  ******************************************************************************/
+void USB_DEVICE(void)  __attribute__ ((section(".icode")));
 void USB_DEVICE(void) {
     int pipe_restore=M66591_CPORT_CTRL0;
-    logf("mxx: INT BEGIN tick: %d\n", (int) current_tick);
+    logf("\nmxx: INT BEGIN tick: %d", (int) current_tick);
     
     logf("mxx: sMAIN0: 0x%04x, sRDY: 0x%04x", 
         M66591_INTSTAT_MAIN, M66591_INTSTAT_RDY);
@@ -548,7 +618,7 @@ void USB_DEVICE(void) {
     
     /* Restore the pipe state before the interrupt occured */
     M66591_CPORT_CTRL0=pipe_restore;
-    logf("\nmxx: INT END");
+    logf("mxx: INT END\n");
 }
 
 /*******************************************************************************
@@ -576,7 +646,7 @@ int usb_drv_request_endpoint(int type, int dir) {
 
     if (type == USB_ENDPOINT_XFER_BULK) {
         /* Enable double buffer mode (only used for ep 1 and 2) */
-        pipecfg |= 1<<9; 
+        pipecfg |= 1<<9 | 1<<8; 
         
         /* Bulk endpoints must be between 1 and 4 inclusive */
         ep=1;
@@ -591,6 +661,8 @@ int usb_drv_request_endpoint(int type, int dir) {
     } else if (type == USB_ENDPOINT_XFER_INT) {
         ep=5;
         
+        pipecfg |= 1<<13; 
+        
         while(M66591_eps[ep].busy && ep++<7);
         
         /* If this reached 7 the endpoints were all busy */
@@ -612,14 +684,16 @@ int usb_drv_request_endpoint(int type, int dir) {
     
     M66591_PIPE_CFGSEL=ep;
     
-    /* Enable pipe (15) and continuous transfer mode (8) */
-    pipecfg |= 1<<15 | 1<<8; 
+    /* Enable pipe (15) */
+    pipecfg |= 1<<15; 
     
     pipe_handshake(ep, PIPE_SHAKE_NAK);
 
     /* Setup the flags */
     M66591_PIPE_CFGWND=pipecfg;
     
+    pipe_init(ep);
+    
     logf("mxx: ep req ep#: %d config: 0x%04x", ep, M66591_PIPE_CFGWND);
 
     return ep | dir;
@@ -664,24 +738,13 @@ void usb_enable(bool on) {
 void usb_drv_init(void) {
     logf("mxx: Device Init");
     
-    /* State left behind by m:robe 500i original firmware */
-    M66591_TRN_CTRL         = 0x8001; /* External 48 MHz clock */
-    M66591_TRN_LNSTAT       = 0x0040; /* "Reserved. Set it to '1'." */
-    
-    M66591_PIN_CFG0         = 0x0000;
     M66591_PIN_CFG1         = 0x8000; /* Drive Current: 3.3V setting */
     M66591_PIN_CFG2         = 0x0000;
     
-    M66591_INTCFG_MAIN      = 0x0000; /* All Interrupts Disable for now */
-    M66591_INTCFG_OUT       = 0x0000; /* Sense is edge, polarity is low */
-    M66591_INTCFG_RDY       = 0x0000;
-    M66591_INTCFG_NRDY      = 0x0000;
-    M66591_INTCFG_EMP       = 0x0000;
-    
-    M66591_INTSTAT_MAIN     = 0;
-    M66591_INTSTAT_RDY      = 0;
-    M66591_INTSTAT_NRDY     = 0;
-    M66591_INTSTAT_EMP      = 0;
+    M66591_TRN_CTRL         = 0x8000; /* External 48 MHz clock */
+    M66591_TRN_CTRL         |=0x0001;
+
+    M66591_INTCFG_MAIN      |=0x8000; /* Enable VBUS interrupt */
 }
 
 /* fully enable driver */
@@ -713,17 +776,17 @@ void usb_attach(void) {
     M66591_TRN_CTRL &= ~(1<<7);
 #endif
 
-    /* Enable oscillation buffer */
+    /* Enable oscillation buffer XCKE */
 	M66591_TRN_CTRL |= (1<<13);
 
     udelay(1500);
 
-    /* Enable reference clock, PLL */
+    /* Enable reference clock, PLL RCKE */
     M66591_TRN_CTRL |= (3<<11);
 
     udelay(9);
 
-    /* Enable internal clock supply */
+    /* Enable internal clock supply SCKE */
     M66591_TRN_CTRL |= (1<<10);
 
     /* Disable PIPE ready interrupts */
@@ -744,7 +807,7 @@ void usb_attach(void) {
     M66591_DCP_CNTMD |= (1<<8);
     
     /* Set the threshold that the PHY will automatically transmit from EP0 */
-    M66591_DCP_CTRLEN = 128;
+    M66591_DCP_CTRLEN = 256;
     
     pipe_handshake(0, PIPE_SHAKE_NAK);
     
@@ -793,8 +856,7 @@ void usb_drv_exit(void) {
  */
 int usb_drv_send_nonblocking(int endpoint, void* ptr, int length)
 {
-    /* The last arguement for queue specifies the dir of data (true==send) */
-    return mxx_queue(endpoint, ptr, length, true);
+    return mxx_queue(endpoint, ptr, length, true, false);
 }
 
 /* This function begins a transmit (on an IN endpoint), it does not block
@@ -802,8 +864,7 @@ int usb_drv_send_nonblocking(int endpoint, void* ptr, int length)
  */
 int usb_drv_send(int endpoint, void* ptr, int length)
 {
-    /* The last arguement for queue specifies the dir of data (true==send) */
-    return mxx_queue(endpoint, ptr, length, true);
+    return mxx_queue(endpoint, ptr, length, true, true);
 }
 
 /* This function begins a receive (on an OUT endpoint), it should not block
@@ -811,8 +872,7 @@ int usb_drv_send(int endpoint, void* ptr, int length)
  */
 int usb_drv_recv(int endpoint, void* ptr, int length)
 {
-    /* Last arguement for queue specifies the dir of data (false==receive) */
-    return mxx_queue(endpoint, ptr, length, false);
+    return mxx_queue(endpoint, ptr, length, false, false);
 }
 
 /* This function checks the reset handshake speed status 
diff --git a/firmware/export/config-mrobe500.h b/firmware/export/config-mrobe500.h
index d9dc054..9d04aac 100644
--- a/firmware/export/config-mrobe500.h
+++ b/firmware/export/config-mrobe500.h
@@ -207,7 +207,7 @@
 /* enable these for the usb stack */
 #define CONFIG_USBOTG       USBOTG_M66591
 #define USE_ROCKBOX_USB
-//#define USB_ENABLE_SERIAL
+
 #define HAVE_USBSTACK
 //#define HAVE_USB_POWER
 //#define USBPOWER_BUTTON     BUTTON_POWER
@@ -216,6 +216,7 @@
 #define USB_NUM_ENDPOINTS   7
 #define USB_VENDOR_ID       0x07b4
 #define USB_PRODUCT_ID      0x0281
+#define HAVE_USB_HID_MOUSE
 
 /* Define this if hardware supports alternate blitting */
 #define HAVE_LCD_MODES LCD_MODE_RGB565 | LCD_MODE_YUV | LCD_MODE_PAL256
diff --git a/firmware/export/usb.h b/firmware/export/usb.h
index c380ac5..d432b39 100644
--- a/firmware/export/usb.h
+++ b/firmware/export/usb.h
@@ -98,10 +98,18 @@ enum {
 #ifdef HAVE_USBSTACK
 /* USB class drivers */
 enum {
+#ifdef USB_ENABLE_STORAGE
     USB_DRIVER_MASS_STORAGE,
+#endif
+#ifdef USB_ENABLE_SERIAL
     USB_DRIVER_SERIAL,
+#endif
+#ifdef USB_ENABLE_CHARGING_ONLY
     USB_DRIVER_CHARGING_ONLY,
+#endif
+#ifdef USB_ENABLE_HID
     USB_DRIVER_HID,
+#endif
     USB_NUM_DRIVERS
 };
 
diff --git a/firmware/target/arm/tms320dm320/mrobe-500/usb-mr500.c b/firmware/target/arm/tms320dm320/mrobe-500/usb-mr500.c
index 1fbc1ce..06a5011 100644
--- a/firmware/target/arm/tms320dm320/mrobe-500/usb-mr500.c
+++ b/firmware/target/arm/tms320dm320/mrobe-500/usb-mr500.c
@@ -30,32 +30,44 @@
 void usb_init_device(void) {
     logf("mxx: SOC Init");
 
-    /* The EMIF timing that is currently used may not be apropriate when the 
-     *  device is boosted.  The following values were used with sucess too:
+    /* The following EMIF timing values are from the OF:
      *      IO_EMIF_CS4CTRL1 = 0x66AB;
      *      IO_EMIF_CS4CTRL2 = 0x4220; 
+     *
+     * These EMIF timing values are more agressive, but appear to work as long
+     *  as USB_TRANS_BLOCK is defined in the USB driver:
+     *      IO_EMIF_CS4CTRL1 = 0x2245;
+     *      IO_EMIF_CS4CTRL2 = 0x4110; 
+     *
+     * When USB_TRANS_BLOCK is not defined the USB driver does not work unless
+     *  the values from the OF are used.
      */
+    
     IO_EMIF_CS4CTRL1 = 0x2245;
     IO_EMIF_CS4CTRL2 = 0x4110; 
 
-    IO_GIO_DIR0 &= ~(1<<2);
-    IO_GIO_INV0 &= ~(1<<2);
-    IO_GIO_FSEL0 &= ~(0x03);
+    /* Setup the m66591 reset signal */
+    IO_GIO_DIR0     &= ~(1<<2); /* output */
+    IO_GIO_INV0     &= ~(1<<2); /* non-inverted */
+    IO_GIO_FSEL0    &= ~(0x03); /* normal pins */
+    
+    /* Setup the m66591 interrupt signal */
+    IO_GIO_DIR0     |= 1<<3;    /* input */
+    IO_GIO_INV0     &= ~(1<<3); /* non-inverted */
+    IO_GIO_IRQPORT  |= 1<<3;    /* enable EIRQ */
+    
+    udelay(100);
     
     /* Drive the reset pin low */
-    IO_GIO_BITCLR0 = 1<<2;
+    IO_GIO_BITCLR0  = 1<<2;
 
     /* Wait a bit */
-    udelay(3);
+    udelay(100);
 
     /* Release the reset (drive it high) */
-    IO_GIO_BITSET0 = 1<<2;
-    
-    udelay(300);
+    IO_GIO_BITSET0  = 1<<2;
     
-    IO_GIO_DIR0 |= 1<<3;
-    IO_GIO_INV0 &= ~(1<<3);
-    IO_GIO_IRQPORT |= 1<<3;
+    udelay(500);
 
     /* Enable the MXX interrupt */
     IO_INTC_EINT1 |= (1<<8); /* IRQ_GIO3 */
diff --git a/firmware/target/arm/tms320dm320/system-dm320.c b/firmware/target/arm/tms320dm320/system-dm320.c
index d1f2ff1..434b006 100644
--- a/firmware/target/arm/tms320dm320/system-dm320.c
+++ b/firmware/target/arm/tms320dm320/system-dm320.c
@@ -102,7 +102,7 @@ static const unsigned short const irqpriority[] =
     IRQ_ICE,IRQ_ARMCOM_RX,IRQ_ARMCOM_TX,IRQ_RESERVED
 }; /* IRQ priorities, ranging from highest to lowest */
 
-static void (* const irqvector[])(void) =
+static void (* const irqvector[])(void) __attribute__ ((section(".idata"))) =
 {
     TIMER0,TIMER1,TIMER2,TIMER3,CCD_VD0,CCD_VD1,
     CCD_WEN,VENC,SERIAL0,SERIAL1,EXT_HOST,DSPHINT,
@@ -222,11 +222,16 @@ void system_init(void)
     
     /* setup the clocks */
     IO_CLK_DIV0=0x0003;
+    
+    /* SDRAM Divide by 3 */
     IO_CLK_DIV1=0x0102;
     IO_CLK_DIV2=0x021F;
     IO_CLK_DIV3=0x1FFF;
     IO_CLK_DIV4=0x1F00;
     
+    /* 27 MHz input clock:
+     *  PLLA = 27*11/1
+     */
     IO_CLK_PLLA=0x80A0;
     IO_CLK_PLLB=0x80C0;
     
@@ -286,6 +291,7 @@ void system_init(void)
     ttb_init();
     /* Make sure everything is mapped on itself */
     map_section(0, 0, 0x1000, CACHE_NONE);
+    
     /* Enable caching for RAM */
     map_section(CONFIG_SDRAM_START, CONFIG_SDRAM_START, MEM, CACHE_ALL);
     /* enable buffered writing for the framebuffer */