How to Develop Firmware for a Direct Drive TFT
Contents
1. SUIHidePageO This hides the page while we are redrawing Draw the icons selected in the G_ddChoices array ChoicesDraw amp G_aTsWindow G_ddChoices Draw choices SUIShowPage0 Show the page now that everything has been drawn while G_ddExit Wait for a touchscreen event or timeout ChoicesUpdate amp G_aTsWindow G_ddChoices queue 100 application code here UEZLCDClose lcd End access to the LCD display UEZTSClose ts queue Close a previously opened touchscreen device UEZQueueDelete queue Close the Touch Screen queue Figure 10 Sense Touchscreen Input FUTURE ELECTRONICS www FutureElectronics com Animate Screen Objects The Bouncing Diamonds Application Figure 11 was developed by the Future Electronics System Design Center SDC to highlight the RX62N direct drive fen R ma AAAAAAAAARARRRRAAARAA FPU 15544 7 NOFPU 15544 7 Speed IDLE 205537 85 p Control Timer 151 lt 1 capability The firmware discussed in this section demonstrates variable soeed animation of two bouncing diamond sprites red amp blue together with CPU run time statistics User buttons control speed of animation slow medium and fast As the animation speed increases the CPU IDLE time decreases At the slowest animation speed the CPU IDLE time is above 80 while at the fastest animation speed the CPU IDLE time is above 50 Figure 11 Bouncing Diamonds Application E2. LCD To select an LCD panel in firmware and activate its preset configuration modify the VEZ_DEFAULT_LCD_CONFIG define in file Config_App h as shown below Figure 2 define UEZ_DEFAULT_LCD_CONFIG NLT_NL2432HC22 41B Figure 2 Select LCD used in the Project in file Config_App h Additional firmware may be required when integrating a new LCD panel For example the NLT NL2432HC22 41B requires initialization of its internal registers after reset Refer to the Tips amp Tricks section for more details Direct Drive LCD Device Specific Focus LCD Timing Parameters The firmware to configure the timing parameters for the TFT LCD panel is found in uEZ project file DirectLCD_CNF h The part number of the target LCD panel is in parentheses for example DirectLCD_CNF NLT_NL2432HC22 41B h is the configuration file for the NLT NL2482HC22 41B TFT LCD Modify the LCD timing parameters dot clock frequency pulse width back porch and front porch Figure 3 according to the manufacturer s datasheet Dot Clock Frequency define DOT_CLOCK_FREQUENCY_DATA 6000000L define H_IDOT_PULSE 8 Horizontal pulse width define HIDOT_BACK_PORCH 3 Horizontal back porch define HLDOT_FRONT_PORCH 4 Horizontal front porch define V_LINES PULSE 2 Vertical pulse width define V_LINES_ BACK_PORCH 1 Vertical back porch define V_LINES FRONT_PORCH 1 Vertical front porch Figure 3 LCD Timing Parameters file DirectLCD_CNF NLT_NL2432HC22 4
3. 1B h FUTURE _ ELECTRONICS www FutureElectronics com LCD Resolution amp Orientation Settings To configure the screen resolution modify the LCD resolution parameters H_DOT_DISPLAY and V_LINES_DISPLAY Figure 4 For example to configure the Direct Drive firmware for resolution 240x320 pixels modify the parameters as shown below Figure 4 The firmware may be used to drive an LCD in either landscape or portrait orientation define H_DOT_DISPLAY 240 define V_LINES_DISPLAY 320 Figure 4 Resolution 240x820 Portrait file DirectLCD_CNF NLT_NL2432HC22 41B h LCD Interface Settings The interface settings specify the port and pin assignments for vsync hsync dot clock and backlight The Ex DMA channel and timer unit are also specified The code is found in uEZ project file DirectLCD_CN h Figure 5 define VSYNC_PORT 2 VSYNC connected to Port 2 Pin 4 define VSYNC_PIN 4 define HSYNC_PORT 3 HSYNC connected to Port3 Pin 6 define HSYNC_PIN 2 define DOTCLK_PORT 5 DOTCLK connected to Port 5 Pin 6 define DOTCLK_PIN 6 define LCD_BACKLIGHT_PORT 9 Power to LCD Backlight define LCD_BACKLIGHT_PIN 3 define EXDMAC_DD EXDMACO0 ExDMA Channel define DD_TMR_MTU Specify timer unit used Figure 5 Interface Settings file DirectLCD_CNF h Turn on LCD Control Backlight and Access LCD To turn on the LCD and backlight refer to the table below Table 1 LCD Function VEZ Routing Acc
4. Demo Touchscreen Input 4 Wire Resistive The uEZ provides an API for the touchscreen with a task that polls status and generates events placed on the queue To get access to the touchscreen add an array of type T_choice that holds information about each icon size and type In the example shown below Figure 8 three icons are displayed on the LCD The icons are G_exitIcon to exit the menu G_upArrlcon to increase animation speed and G_downArrlcon to decrease animation speed Each icon has a function associated with it that is called when the icon is pressed For example when the user presses the G_exiticon the touchscreen senses the input and calls function DD_Exit static const T_choice G_ddChoicesj Array to store the icons their locations and the functions they call DD_COLUMN_1_CTRL 20 DD_COLUMN_1_CTRL DD_BUTTON_WIDTH 1 50 DD_Exit G_exitlcon DD_COLUMN_1_CTRL 55 DD_COLUMN_1_CTRL DD_BUTTON_WIDTH 1 85 DD_IncSpd G_ upArricon DD_COLUMN_1_CTRL 85 DD_COLUMN_1_CTRL DD_BUTTON_WIDTH 1 115 DD_DecSpd G_ downArrlicon 0 0 0 0 0 Figure 8 Array to Store Icons Location amp Associated Function when Pressed To use the touchscreen declare a queue to catch the touchscreen events and a handle to the touchscreen Figure 9 T_uezQueue queue queue to catch the touch screen events T_uezDevice ts handle to touch screen Figure 9 Touchscreen Queue FUTURE ELECTR
5. ERROR_NONE error UEZSPIOpen SPI1 amp p gt iSPI open the SPI1 interface if error SYSTEM SYSCRO WORD 0x5A01 disable External Bus if l error UEZTaskDelay 1 Power ON Sequence 5 45 error ISPIWriteCommands p G_IlcdPowerOn_a if error Sequence 46 30 microsecond min wait UEZTaskDelay 1 Sequence 47 Data input start NOP Sequence 48 error ISPIWriteCommands p G_lcdPowerOn_b if error Sequence 49 20 ms min wait UEZTaskDelay 25 Sequence 50 error ISPIWriteCommands p G_IlcdPowerOn_c SYSTEM SYSCRO WORD 0x5A03 enable External Bus UEZSPIClose p gt iSPI close the SPI interface return error Figure 16 Disable External Bus Prior to SPI Transfer FUTURE ELECTRONICS www FutureElectronics com 2 Double Buffer Dynamic Text to Avoid Display Flicker Problem When dynamic text is refreshed rapidly on the LCD for example FreeRTOS run time statistics it can result in display flicker Solution Create a double buffer Figure 17 in the software to manage the text input and output buffer The buffers are swapped periodically Dynamic data is sent to the input buffer while the LCD displays the contents of the output buffer Every fixed time interval the doublebufferFlag is toggled to swap the buffers toggle doublebufferFlag in application code short doublebufferFlag 0 0 buffer1 input buffer2 output 1 buffer1 output buff
6. How to Develop Firmware for a Direct Drive TFT LCD Design with RX62N ae By Daniel Azimov Software Specialist System Design Center Future Electronics EN ESAS A Direct Drive TFT LCD design can drive high quality images on small color displays including QVGA 320x240 and WQVGA 480x272 at 16 bpp color depth 60Hz refresh rate The Direct Drive solution eliminates the need for a standalone external LCD controller the main benefits are cost reduction and smaller design footprint But how to develop firmware for a Direct Drive TFT LCD solution This white paper presents the fundamental elements of a Direct Drive firmware design for the RX62N The device specific focus includes LCD timing parameters resolution settings interface settings backlight control and frame memory access The application specific focus includes draw routines pixels lines boxes and text icons buttons touchscreen input and animation There are code snippets application notes and tips amp tricks Getting Started with RX62N Direct Drive Firmware Development Renesas provides the RX62N Direct Drive LCD low level drivers and GAPI to control the timing signals to the TFT LCD free of charge From this point the developer has to make a choice either develop a standalone application or choose an open source platform compatible with Renesas Direct Drive The firmware design time can be reduced significantly by choosing an open source platform such as uEZ This white paper re
7. ONICS www FutureElectronics com The code to sense the touchscreen input is shown below Figure 10 The UEZQueueCreate function creates a queue for the touchscreen Open and initialize the touchscreen device and pass in the queue by calling function VEZTSOpen The ChoicesDraw function draws the icons in the G_ddChoices array and checks the touchscreen event on each iteration of the while loop When an icon is touched its corresponding function is called To disable touchscreen input close the touchscreen and delete the queue by calling functions VEZTSClose UEZQueueDelete typedef struct T_uezTSFlags iFlags TInt32 iX TInt32 iY TUInt32 iPressure T_uezTSReading void DisplayDemo const T_choice aChoice T_uezDevice Icd uEZ Device Type handle to the display T_pixelColor pixels pointer to the screen an array of pixels T_uezQueue queue Queue to catch Touch Screen events T_uezDevice ts uEZ Device Type handle to Touch Screen UEZQueueCreate creates a queue and returns point to the queue if UEZQueueCreate 1 sizeof T_uezTSReading amp queue UEZ_ERROR_NONE Open up the touchscreen and pass in the queue to receive events if UEZTSOpen Touchscreen amp ts amp gueue UEZ_ERROR_NONE Open the LCD and get the pixel buffer if VEZLCDOpen LCD amp lcd UEZ_ERROR_NONE Returns a pointer to the frame memory in the LCD UEZLCDGetFrameiIcd 0 void amp pixels
8. ach diamond animation is implemented as a FreeRTOS task The tasks are assigned identical priority and time to complete as many trajectory calculations as possible Figure 12 UEZTaskCreate T_uezTaskFunction vUpdateFPUShape FPU UEZ_TASK_STACK_BYTES 128 void 0 UEZ_PRIORITY_NORMAL FPUHandle UEZTaskCreate T_uezTaskFunction vUpdateNoFPUShape NoFPU UEZ_TASK_STACK_BYTES 128 void 0 UEZ_PRIORITY_NORMAL NoFPUHandle Figure 12 Create FreeRTOS Tasks to Perform Animation To create the animation effect the FPU task calls function vUpdateFPUShape to initialize a timer for TaskAppTimerMsecCount msecs The shape position is updated in function fpu_shapeUpdatePosition The previous shape is erased by redrawing it with the pen color set to the background color Then the new shape is drawn at the updated position Figure 13 FUTURE ELECTRONICS www FutureElectronics com define RADIUS_VERT 10 Diamond vertical radius SHAPE fpuShape current shape position SHAPE fpuShapePrev previous shape position TUInt382 vUpdateFPUShape T_uezTask aMyTask void aParams RTOS Task PARAM_NOT_USED aMyTask PARAM_NOT_USED aParams for if enableUpdateFPUShape save fpuShape previous position fpuShapePrev fpuShape Move shape using hardware FPU TaskAppTimerMsecCount TimeToMoveShape while TaskAppTimerMsecCount gt 0 decrement count in another task fpu_shap
9. anel is being refreshed externally There is approximately 5 Bde cma loading on the CPU during normal operation as the Ex DMA unit and the CPU RE have minimal interaction This frees up the CPU to run the application and Ti s i Unit P corre ag periodically write new image data to the external RAM frame buffer Data Bus 16bits RX Series Direct LCD Design Guide p 17 Renesas Electronics Corporation Address RAM Figure 1 Direct drive block diagram FUTURE ELECTRONICS www FutureElectronics com LCD Selection When selecting a TFT LCD for a Renesas Direct Drive RX62N solution choose any panel up to WQVGA resolution 480x272 at 16 bpp color depth The LCD can be any size or orientation portrait or landscape Future Electronics together with FDI offers three Direct Drive TFT LCD solutions e Future FDI RX62N Demo including 3 5 QVGA NLT LCD Portrait e FDI DK 43WQT RX62N including 4 3 WQVGA Tianma LCD Landscape e FDI DK 47WQT RX62N including 4 7 WQVGA Tianma LCD Landscape These TFT LCD panels have integrated touchscreens and there are preset LCD firmware configurations available for each If one of the above is not chosen for the design firmware parameters should be modified as described below in the Direct Drive LCD device specific focus The remainder of the white paper discusses a Direct Drive firmware design based on the 3 5 NLT NL2482HC22 41B QVGA 240x320
10. commends the latter approach and describes the Direct Drive firmware design within this framework Another firmware consideration is whether to use a real time operating system such as FreeRTOS Although it is not absolutely necessary for a Direct Drive application an RTOS will provide additional benefits such as a real time kernel and CPU usage monitoring Recommended Tools The following development tools are recommended to develop a Direct Drive application E Choose one of the following RX62N LCD Touchscreen Development Kits Future FDI RX62N Demo DK 43WQT RX62N DK 47WQT RX62N E LEZ Development Platform E FreeRTOS Operation System E Renesas High Performance Embedded Workshop E Segger J Link Lite How Does the Direct Drive Hardware Work The CPU offloads the work of refreshing the TFT panel to the external DMA Ex DMA controller inside the MCU Figure 1 The Ex DMA takes control of the 16 bit external bus by driving the address lines and controlling the read strobe to the external RAM The RAM frame buffer outputs a 16 bit data word for one pixel of RGB data The MCU s timer unit clocks the RGB pixel data into the TFT panel This process is repeated for each RGB pixel once per frame Driving the TFT LCD using the external DMA frees up the CPU to spend the bulk of its processing time on the application software The MCU can access internal memory and peripherals using its internal bus Pl 4g p _Optionat External Storage while the TFT p
11. e Electronics representative E 3 5 NLT LCD Carrier Board Carrier Board for NLT 3 5in TFT LCD 240x320 Designed by Future Electronics System Design Center SDC as part of the Future FDI 3 5in NLT RX62N demo as stated above Reference design available upon request E NLT 3 5 TFT LCD 240x320 NL2432HC22 41B Portrait Technical Resources E www FutureElectronics com Renesas E www rxmcu com USA E www teamfdi com E The uEZ source code and documentation can be downloaded from www sourceforge net projects uez E FreeRTOS is available from http www freertos org Renesas Electronics America is the exclusive sales and marketing channel in the Americas for LCD Modules from NLT Technologies FUTURE ELECTRONICS www FutureElectronics com
12. e on chip ROM and the external bus Figure 14 System Control Register O SYSCRO RX62N Group RX621 Group User s Manual Hardware p 124 RO1UHOO33EJ0110 Rev 1 10 Renesas Electronics Corporation Problem The SPI Interface requires access to the external bus to initialize the LCD internal registers On startup the uEZ function UEZBSPSDRAMInit enables the external bus Figure 15 When the external bus is enabled the SPI interface CS cannot go to the LOW state and the transfer will not occur FUTURE ELECTRONICS www FutureElectronics com Description Initialize the external SDRAM void UEZBSPSDRAMInit void TUInt32 delay Configure port pins Enable On Chip ROM amp External BUS SYSTEM SYSCRO WORD 0x5A03 Figure 15 UEZBSPSDRAMInit Function Enables External BUS Solution The HAL Hardware Abstraction Layer is a layer of firmware that controls the hardware directly The function SPIConfigure is a HAL function that configures the SPI interface Figure 16 Before starting the SPI transfer disable the external bus by setting the SYSTEM SYSCRO WORD to Ox5A01 This clears SYSCRO Bit b1 Then write data to the LCD Registers via the SPI interface by calling function SPIWriteCommands When the SPI transfer is complete set SYSTEM SYSCRO WORD to Ox5A03 to enable the external bus for normal LCD operation static T_uezError ISPIConfigure T_NL2432HC22_41KWorkspace p T_uezError error UEZ_
13. eUpdatePosition amp fpuShape move the shape erase fpuShape in previous position set_pen_color amp G_aTsWindow BLACK Sets the pen color set_fill_color amp G_aTsWindow BLACK Sets the fill color put_diamond amp G_aTsWindow int fpuShapePrev x x Virtual X position of diamond int fpuShapePrev y y Virtual Y position of diamond RADIUS_HORIZ rx Radius for horizontal RADIUS_VERT ry Radius for vertical draw fpu shape set_pen_color amp G_aTsWindow BLACK Sets the pen color set_fill_color amp amp G_aTsWindow RED Sets the fill color put_diamond amp G_aTsWindow int fpuShape x x_ Virtual X position of diamond int fpuShape y Iy_ Virtual Y position of diamond RADIUS_HORIZ rx_ Radius for horizontal RADIUS_VERT ry Radius for vertical UEZTaskDelay TaskldleTime return 0 Figure 13 FreeRTOS Task to Animate a Shape The red diamond animation trajectory is calculated with floating point math enabled FPU simply by changing the compiler options to generate native floating point code causing it to bounce much faster approximately 3 5 times faster than the blue diamond The blue diamond trajectory is calculated with native floating point code generation turned off by the compiler NOFPU The FreeRTOS API collects real time data on the absolute amp percentage of CPU processing time used by each task The CPU Stats are displayed in the upper right hand corn
14. er of the TFT LCD highlighting percentage of CPU IDLE time This is a useful feature to enable in FreeRTOS to measure system performance Animation requires frequent access to the frame buffer during vertical blanking Refer to the Tips amp Tricks section for more details FUTURE ELECTRONICS www FutureElectronics com Tips amp Tricks 1 How to Initialize TFT LCD Internal Registers via SPI Some LCDs may require initialization of internal registers For example the NL2432HC22 41B LCD requires data be written into the internal registers after applying RESET from serial interface pins CS SCL and Sl The RX62N System Control Register O bit 61 controls whether the external bus is enabled or disabled Figure 14 3 2 3 System Control Register 0 SYSCRO Address 0008 0006h b15 b14 b13 b12 b11 b10 b9 b8 KEY 7 0 Value after reset 0 0 0 0 0 0 0 0 Value after reset b7 b6 b5 b4 b3 b2 b1 bO ee EE E 0 0 0 0 0 0 0 1 Bit Symbol Bit Name Description R W bo ROME On Chip ROM Enable 0 The on chip ROM is disabled RAW 1 The on chip ROM is enabled b1 EXBE External Bus Enable 0 The external bus is disabled RAW 1 The external bus is enabled b7 to b2 Reserved These bits are always reas as 0 The write value should always R W be 0 b15 to b8 KEY 7 0 SYSCRO Key Code 5Ah Modifying SYSCRO is enabled R W Other codes Modifying SYSCRO is disabled These bits are always read as 00h SYSCRO is used to enable or disable th
15. er2 input double buffer 1 2 dimensional array of strings char buffer1 Stats MAX_NUM_TASK_STRINGS MAX_TASK_STRING_SIZE double buffer 2 2 dimensional array of strings char buffer2Stats MAX_NUM_TASK_STRINGS MAX_TASK_STRING_SIZE get pointer to input buffer static char getDoubleBufferPtrln int index if doublebufferFlag flag to choose input buffer return amp buffer1 Stats index 0 doublebufferFlag 0 buffer1 input else return amp buffer2Stats index 0 doublebufferFlag 1 buffer2 input get pointer to output buffer static char getDoubleBufferPtrOut int index if doublebufferFlag flag to choose output buffer return amp buffer1 Stats index 0 doublebufferFlag 1 buffer1 output else return amp buffer2Stats index 0 doublebufferFlag 0 buffer2 output Figure 17 Double Buffer Text Strings to Avoid Display Flicker 3 Crystal Dot Clock Frequency amp Bclk Frequency When choosing the LCD for the design verify the DOT_CLOCK_FREQUENCY specified by the manufacturer and choose the crystal accordingly For the RX62N BCLK_FREQUENCY Crystal Frequency 8 1 or 2 or 4 or 8 For more information refer to p 238 of the RX62N Group RX621 Group User s Manual Hardware The DOT_CLOCK_FREQUENCY must be an even divisor of the BCLK_FREQUENCY For example if the BCLK_FREQUENCY is 48 MZ the DOT_CLOCK_FREQUENCY can be 24MH 12MHZ 6 MHZ 4MHZ etc If the DOT_CLOCK_FREQUENCY i
16. ess the LCD device UEZLCDOpen Get a pointer to the frame memory in the LCD display UEZLCDGetFrame Control the backlight intensity UEZLCDBacklight Turn the LCD on UEZLCDOn Icd Turn the LCD off UEZLCDOff Icd Table 1 LCD Access API y wl FUTURE ELECTRONICS www FutureElectronics com Sample code to access the LCD and control the backlight is shown below Figure 6 T_uezDevice Icd T_pixelColor pixels if VEZLCDOpen LCD amp lcd UEZ_ERROR_NONE UEZLCDGetFramei cd 0 void amp pixels UEZLCDBacklight Icd 0 set backlight off UEZLCDOniIcd UEZLCDBacklight Icd 255 set backlight to max intensity Figure 6 Access LCD and Turn On Backlight This ends the discussion of the Direct Drive LCD device specific focus The application specific focus is discussed below Direct Drive LCD Application Specific Focus Display Pixels Lines Boxes amp Text The uEZ provides a graphics library for drawing pixels lines boxes and text First open and draw a window by calling the uEZ window_open routine A window is defined by its left top coordinate and right bottom coordinate and border width Choose the window background color Call uEZ drawing routines to draw pixels lines boxes and shapes Call UEZ font routines to display text control font type size and transparency Pen color text color and fill color can also be modified dynamically Icons Buttons Display To add an application ico
17. its for the ExDMA transfer to end This will result in undesired screen artifacts To resolve this issue in firmware wait for the LCD_BusActive flag to be cleared indicating ExDMA transfer is finished before modifying the contents of the frame buffer Conclusion The essential elements of a successful Direct Drive firmware design are presented By using the recommended hardware and software libraries the developer can shorten the Direct Drive firmware design cycle considerably Renesas provides the GAPI library and Direct Drive LCD low level drivers to control the timing signals to the TFT LCD free of charge The uEZ GUI Software and FreeRTOS are open source software tools compatible with Renesas RX62N Direct Drive TFT LCD solutions providing advanced graphical display effects for a cost effective design FUTURE ELECTRONICS www FutureElectronics com Direct Drive Demo Hardware E Future Electronics FDI 3 5 NLT RX62N demo including LCD board baseboard and SOMDIMM module Can be borrowed through your local Future Electronics representative E FDI 4 3 Tianma demo including LCD board baseboard and SOMDIMM module Can be purchased using the following part number DK 43WQT RX62N Can be borrowed through your local Future Electronics representative E FDI 4 7 Tianma demo including LCD board baseboard and SOMDIMM module Can be purchased using the following part number DK 47WQT RX62N Can be borrowed through your local Futur
18. n to the project first create a bitmap image in Targa format using an Image Editor Save the image to file Newlcon tga and copy it to the Images folder In this folder there is a batch file called convert bat that converts the binary tga file into a C variable definition It contains the binary data in a format that can be compiled by the uEZ Run the batch file convert bat to create the file Newlcon h Add the icon to the HEW project by right clicking on the project name in the HEW Project Explorer and select Add Files Navigate to the images folder and select file Newlcon h From the Project Explorer open the file UDClmages c find the list of include directives and add the line include images Newlcon h Go back to the Project Explorer and open the file UDCIlmages h then ada extern const TUInt8 G_newlcon FUTURE ELECTRONICS www FutureElectronics com Build the project to add the application icon to the project Use the code shown below Figure 7 to display the application icon static const T_appMenuEntry mainmenu_entries Direct Drive Demo DisplayDemo G_newlcon 0 Oh static const T_appMenu mainmenu PROJECT_NAME VERSION_AS_ TEXT Main Menu mainmenu_entries EFalse cannot exit AppMenu amp mainmenu Figure 7 Display Icon on LCD When the icon represented by G_newlcon is pressed on the touchscreen the application calls function Display
19. nitialized in firmware is not an even divisor of BCLK_FREQUENCY a compilation error will be generated during the project build Select a crystal that it is an even multiple of the DOT_CLOCK_FREQUENCY For example if the manufacturer recommended DOT_CLOCK_FREQUENCY is 6 Mt choose a crystal oscillator that is an even multiple of GMHZ i e 12MHz FUTURE ELECTRONICS www FutureElectronics com 4 CPU Access to Frame Buffer The ExDMA and CPU share access to the external memory frame buffer For approximately 50 of the LCD refresh period the ExDMA moves data from the SRAM to the LCD During this time the CPU tasks that access the external memory should be suspended After the ExDMA transfer is finished the CPU can access the frame buffer to update the LCD display Figure 18 16 6 msec 60Hz refresh rate 50 of Period 50 of Period PPPS oars aS a a ar eras oe E 7 DoS Pa OO a a OS a eer eee SISESTI eres d IEEE SIII SS V sync ORO OR OOO Xx ERLER RRRS J RL RERE ERRE CPU cannot access CPU can access frame buffer frame buffer ExDMA gt ExDMA finished moving from gt moving data from data SRAM to LCD SRAM to LCD Figure 18 CPU Access to Frame Buffer after ExDMA Transfer Courtesy Renesas Electronics Corporation There is no hardware synchronization between the ExDMA and CPU access to the frame buffer The effect of unsynchronized frame buffer access may be stalling of the CPU core while it wa
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