Skip to main content

JTAG - Test Access Port (TAP)Controller based Xilinx FPGA configuration using Raspberry Pi

JTAG - Joint Test Action Group is an IEEE 1149.1 standard used in many silicon devices for programming and debugging purposes. Xilinx FPGAs support this JTAG protocol for their configuration. Here I have designed a JTAG FPGA bitstream programmer using Raspberry Pi which programs the bit file into FPGA in fraction of seconds!

 JTAG physical bus has four lines:
  1. TMS (Test Mode Select)
  2. TDI (Test Data In)
  3. TDO (Test Data Out)
  4. TCK (Test Clock)
Components Used: 
  • Raspberry-Pi
  • Xilinx Spartan 3E FPGA (XC3S250E in Papilio One)
  • Jumper wires


BLOCK DIAGRAM:




TAP CONTROLLER:


The TAP(Test Access Port) controller is a state machine inside the FPGA which changes it's state based on TMS input. For instance, let us assume that the state machine is in "Test-Logic-Reset" state. Now if I drive the TMS pin low and toggle the TCK pin, the state machine will go to "Run-Test/ Idle" state. This is how we move to different states.



 Note that we don't know in which state the state machine will be once the device is switched on. But a careful observation shows that in whichever state the SM (state-machine) be, if TMS pin is held high for 5 TCK cycles, the machine goes to "Test-Logic-Reset" state. So whenever a device is switched on, if we drive TMS high for 5 cycles, it will come to Reset state.

 Other important states are "SHIFT-IR" (Instruction Register) and "SHIFT-DR" (Data Register). So to do anything meaningful, we need to drive the state machine to SHIFT-IR state and send the instruction OPCODEs through TDI line. For example, in Xilinx Spartan-3 FPGAs, the device IDCODE instruction is 001001. So after shifting 001001 in TDI line while in "SHIFT-IR" state, we have to go to "SHIFT-DR" state and toggle TCK and read TDO line to receive the device IDCODE.

 Now after enquiring the Device ID, we can send CFG_IN (configuration input) instruction and then program the bit stream into FPGA through TDI. The GPIO pins of Raspberry-Pi are used as TMS,TDI,TCK & TDO pins and an application written in C toggles these GPIO pins & programs the bit file into FPGA.

 After programming the bit file, Raspberry-Pi shifts in JSTART instruction into IR and then executes RUN-TEST sequence which will initiate the program execution inside FPGA.

DEMO:



Comments

Post a Comment

Popular posts from this blog

Shell Scripting to Display Bar Graphs in Linux Terminal

 This week was quite hectic for me with course assignments and their merciless deadlines. One such assignment in Advanced Computer Architecture  was simulation of various benchmarks in alpha architecture in simplescalar , a well-known computer architecture simulator. I was supposed to run a total of 4 benchmarks with different configurations of cache memory, instruction issue widths, commit widths, in-order execution modes, etc and I had to plot the required performance parameters for every benchmark. A conservative estimate would be around 40 plots!  Since the simulation platform was Linux, I could breathe a sigh of relief since most things can be automated using a powerful tool called shell. Scripting made my life easier here since I can automate a bunch of simulations without having to keep an eye on each and every simulation which would take anywhere from 20 minutes to 20 hours.  The problem arose when it came to plotting the performance results. Becau...
1 comment
Read more

Programming STM32 ARM microcontrollers in Arch Linux

Once upon a time, not so long ago, the 8-bit microcontrollers were ruling the hobbyist embedded world. But today, the 32-bit ARM Cortex Microcontrollers are so inexpensive and power efficient that there is no good reason to ignore them. Here, let us see how to program a STM32 ARM cortex Microcontroller in Linux environment. The specific microcontroller used here is an STM32F103C8 (ARM cortex M3) programmed in Arch linux. Components Generic STM32F103 board (blue pill) STLINK-V2 (STM32 programmer) Female-Female connectors All the above components can be bought from ebay for less than $10 total. The STLINK-V2 is optional since you can use any of USB-SERIAL converters like FT232, CP2102, PL2303, CH340 and the built-in UART bootloader of STM32 chip to program. So if you already have any of the above serial converters, you don't really need STLINK to program the STM32F103 microcontroller. But STLINK helps if you plan to use in circuit debugging functionalities. Software The...
Post a Comment
Read more