expanding the micro blaze system

Expanding the MicroBlaze SystemIntroduction

This week, we will expand our MicroBlaze design to a full-blown system providing the following features:

• VGA output• LCD output• 16-bit memory controller• code and data stored in external memory

Instead of performing the required steps to upgrade your design from week 4 yourself, we will present a guided tour through the complete design here. Take your time to look through the code, and try simple variations on the given project. You will be implementing your own peripherals during the next extercises!

SoC Course WS 2002/2003 Week #7

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VGA outputThe VGA output may be used to display textural information on a standard PC monitor. The VGA peripheral comes complete with drivers, so that the peripheral may be used to redirect STDOUT.The peripheral‘s hardware design files are located in the opb_peripherals/te_vga_v1_00_a directory. The peripheral‘s driver source files are located in the drivers/drv_te_vga_v1_00_a directory. You are invited to browse through these files for further insights.The peripheral is instantiated in the MHS file as follows:SELECT slave te_vga

CSET attribute INSTANCE = vgaconCSET attribute HW_VER = 1.00.aCSET attribute C_BASEADDR = 0xF4800000CSET attribute C_HIGHADDR = 0xF4FFFFFFCSET signal clk25 = clk25CSET signal r = rCSET signal g = gCSET signal b = bCSET signal rb = rbCSET signal gb = gbCSET signal bb = bbCSET signal hsync = hsyncCSET signal vsync = vsync

END

The peripheral is mapped into the main memory at address F4800000. The video screen is organized in 32 lines with 64 characters each. This results in 2kB of video memory. As the address is not fully decoded, the video memory is mirrored throughout the complete area from C_BASEADDR to C_HIGHADDR.The signals r,g,b and rb, gb, bb carry the color information for up to 64 colors. The analog signals required by the VGA monitor are created using a passive resistor network. The horizontal and vertical sync pulses are created from the hsync and vsync signals. In addition to these outputs, the VGA peripherals requires the separate clock input clk25 which provides a 25MHz pixel clock. As standard VGA monitors require relatively high accuracy on their timings, a suitable clock cannot be derived from the 48MHz input used for the MicroBlaze cpu.The drivers for the VGA peripheral are specified in the MSS file as follows:SELECT INSTANCE vgacon

CSET attribute DRIVER = drv_te_vgaCSET attribute DRIVER_VER = 1.00.a

END

To redirect stdout to the VGA, replace the STDOUT definition as follows:# SET attribute STDOUT = uartSET attribute STDOUT = vgacon

Questions• what is the screen resolution in pixels?• what is the size of the character generator ROM in bytes?• draw a simple block diagram of the VGA peripheral showing the bus

interface, the timing generator, the video memory, and the character generator• what happens, if output reaches line 33, how is scrolling implemented? Are

there any other solutions?• which peripheral would you prefer to print debug messages, UART or

VGA? why?


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LCD outputThe LCD output may be used to display textural information on-board. While usage of the LCD panel eases handling, the LCD has some significant drawbacks:

• timing is slow• display is small• LCD has own display buffer• requires 12 pins

Typical cycle time of LCD controllers is 500ns, which is a long time for a CPU running at 48MHz. The display is only 2 lines with 16 characters each, which is not enough for sophisticated output. The display provides its own display buffer, which makes implementation of scrolling difficult or very slow. Still, as no additional monitor is required, the LCD is a useful peripheral for simple text output.The peripheral‘s hardware design files are located in the opb_peripherals/te_lcd_v1_00_a directory. The peripheral‘s driver source files are located in the drivers/drv_te_lcd_v1_00_a directory.The peripheral is instantiated in the MHS file as follows:SELECT SLAVE te_lcd

CSET attribute INSTANCE = lcdconCSET attribute HW_VER = 1.00.aCSET attribute C_BASEADDR = 0xF3800000CSET attribute C_HIGHADDR = 0xF38000FFCSET signal lcd_rs = lcd_rsCSET signal lcd_rwn = lcd_rwnCSET signal lcd_e = lcd_eCSET signal lcd_dr = lcd_drCSET signal lcd_db = lcd_db

END

The driver is specified in the MSS file as follows:SELECT INSTANCE lcdcon

CSET attribute DRIVER = drv_te_lcdCSET attribute DRIVER_VER = 1.00.a

END

Before printing to the LCD, the controller needs to be initialized. To do so, put the following line into your code:

lcd_init();This will initialize your display with an empty screen, cursor off, and an 8-bit interface to the MicroBlaze system.Questions

• is it possible to attach the LCD controller to an 8-bit memory bus?• how would you implement scrolling? are there alternatives?


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memory controllerThe memory controller attaches external 16-bit memory to the 32-bit MicroBlaze system using dynamic bus resizing. This latter is the key feature required, to execute program code from external 16-bit memory. To maximize CPU performance, the memory controller implements different timings for RAM read, RAM write, and access to the Flash memory.The peripheral‘s hardware design files are located in the opb_peripherals/te_mem_v1_00_a directory. The peripheral‘s driver source files are located in the drivers/drv_te_mem_v1_00_a directory.The peripheral is instantiated in the MHS file as follows:SELECT SLAVE te_mem

CSET attribute INSTANCE = memconCSET attribute HW_VER = 1.00.aCSET attribute C_BASEADDR = 0x00800000CSET attribute C_HIGHADDR = 0x00FFFFFFCSET signal mem_a = mem_aCSET signal mem_d = mem_dCSET signal mem_wen = mem_wenCSET signal flash_cen = flash_cenCSET signal flash_oen = flash_oenCSET signal flash_rdy = flash_rdyCSET signal flash_8n = flash_8nCSET signal ram_csn = ram_csnCSET signal ram_oen = ram_oenCSET signal ram_blen = ram_blenCSET signal ram_bhen = ram_bhenCSET signal cpld_csn = cpld_csnCSET signal cpld_rwn = cpld_rwn

END

Beginning with address 0x00800000, the memory map is as follows:0080_0000 - 0087_ffff SRAM00c0_0000 - 00c3_ffff Flash (factory configuration)00c4_0000 - 00c7_ffff Flash (user configuration)00c8_0000 - 00cf_ffff Flash (application space)00e0_0000 push buttons00e0_0002 dip switch00e0_0004 LEDs

The driver is specified in the MSS file as follows:SELECT INSTANCE memcon

CSET attribute DRIVER = drv_te_memCSET attribute DRIVER_VER = 1.00.a

END

The driver provides code to access the flash. Please do not program the flash, unless instructed to do so. This will save your tutor some time!!! Thank you.Questions

• draw a simple diagram illustrating how the memory bus timing is generated• what are the access times for RAM read, RAM write, and Flash? could this

be tweaked to run faster?


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running code from external memoryThe maximum amount of memory implemented inside an XC2S300E part is 8kB. This is not enough for sophisticated programs, especially as part of the memory is already utilized by the peripherals. The solution is, to store code and data in external memory.Typically, program code is store in non-volatile memory, i.e. the on-board flash. Storing your code in the flash memory leads to several problems:

• flash is read-only. this is a problem for initialized data• segmenting code and data according to access attributes is complicated• flash is slow. this reduces the overall performance of the system

To overcome these problems, the code and data are stored in flash, but are copied into the RAM during system start-up. This functionality is implemented using some stub code:main(){ long i, j;

const unsigned short* src;unsigned short* dst;void (*UserEntry)(void)= (void (*)(void))SRAM_BASEADDR;

src = (unsigned short*)FLASH_BASEADDR_APPL;dst = (unsigned short*)SRAM_BASEADDR;for (i= 0; i< FLASH_SIZE; i++){ *dst++ = *src++;}

UserEntry();}

The stub is compiled into the object module flashstub.out using the same options as you used in your previous projects. The stub is stored in the LMB memory with the following line in your MHS file:SET attribute EXECUTABLE = code/flashstub.out

Please note, that the LMB contents for debugging and bootstrap modes remains unchanged:SET attribute XMDSTUB = code/xmdstub.outSET attribute BOOTSTRAP = code/bootstub.out

The user firmware is compiled using the bootstrap option and its base address at the beginning of the SRAM. We may now define plenty of stack space. See the following gcc instruction in the Makefile:code/system.out : lib/libc.a lib/libm.a $(PROGRAM_SOURCES)

mb-gcc \-g \-mxl-gp-opt \-xl-mode-bootstrap \-I./include \-L./lib \-Wl,-defsym -Wl,_STACK_SIZE=0x4000 \-Wl,-defsym -Wl,_TEXT_START_ADDR=0x00800000 \$(PROGRAM_SOURCES) \-o code/system.out

Questions• illustrate the contents of LMB and external RAM for XMDSTUB and

EXECUTABLE modes


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expanding the micro blaze system

Education