FPGAWorkshop13notes

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These notes are intended to highlight bits of information from the Xilinx KCPSM3 manual distributed with the microprocessor

Xilinx Picoblaze

KCPSM3 - An 8 Bit Microcontroller for Xilinx Spartan 3 & Virtex 2/4 devices

What is kcpsm3

Very Simple microcontroller. Can be used for data processing or as a complex state machine.

KCPSM - (K)constant Coded Programmable State Machine

Its very small - 96 Spartan3 slices + 1 block ram

Our boards - 4656 slices -> that is 2% of the slice resources!

Entirely embedded in the fpga fabric - integrates with all the logic you've already been writing!

kcpsm is small

Konstant explained - notice how the mips = 1/2 clock speed?

CPI of the processor is 2. And fixed at 2. that makes it very easy to determine the runtime of a program in an embedded system.


kcpsm3 architecture

architecture is closed (it is a xilinx macro, not a readily readable verilog design) but the architecture is not secret though

simple input port/output based IO, up to 256 addressable 8bit ports/devices 16 general purpose registers 64 byte memory/scratch pad alu with carry/zero flags single interrupt line/acknowledge program counter control/instruction decoder program memory

device features

program memory - 1 18kb block ram! this stores 1024 18 bit instructions. 16 general purpose registers. No dedicated zero register or accumulator alu - does add/sub/add&sub with carry alu - load/and/or/xor bitwise alu - shift/rotates flags and flow control - help determine program flow with carry/zero flags + conditional jump/call instructions interrupts - jumps to a single address (initiates CALL 3FF) - an ISR

using the kcpsm3 used as a verilog module in the design flow. simply copy the kcpsm3.v file into your project and instantiate it kcpsm3 assembler generates a verilog memory file - use that in your design as well. connect the two modules together. alternatively - use the embedded_kcpsm3.v file

instruction set

  1. program control group
    1. unconditional jump
    2. conditional jumps (branches!)
    3. call/return with stack depth of 31
  2. interrupt group
    1. enable/disable interrupt
    2. return from isr & either enable/disable the interrupt
  3. storage group
    1. store/fetch data from the scratch pad
  4. i/o group
  5. arithmetic group
    1. add/sub/compare
      1. work with 2 operands or 1 operand and a constant
  6. logical group
    1. load/and/or/xor/test
      1. work with 2 operands or 1 operand and a constant
  7. shift/rotate group
    1. both left/right shifts available

pointers available

port access

input and output ports available.

very simple with the two cycle operation

  1. 1st cycle - instruction decode
  2. 2nd cycle - instruction execute

Read strobe - not needed, port_id used w/ a mux to determine what gets put on input port. data captured by kcpsm3 on next clock edge.

write strobe - use as a clock enable signal for external circuitry to capture data from out port.

<8 output ports, use 1hot addressing

>8 output ports, use address decoder to enable the correct port

input ports -> leads itself to a multiplexed architecture

reset

synchronous to kcpsm3 clock. blanks the processor and restarts it at address 0x000.

picoblaze assembler

xilinx assembler is a dos program, which accepts .psm (picoblaze assembler) source files and outputs vhdl/verilog files for your use multipass, lots of quick information. don't be afraid to dump the file.

possible to run under wine/dosbox, lots of alternatives available.

program syntax

  1. blank lines are ignored
  2. comments begin with ;
  3. registers - form sX, where X={0,1,2,..9,A,...,E,F}
  4. constants
  5. Data value - 00 ->FF
  6. Port value - 00 ->FF
  7. Address - 000 ->3FF
  8. Line labels: Useful for call and jump instructions!

constant -> define a label used within the program for holding a constant value. like a C macro

namereg -> define a label used within the program for identifying a register. allows for much more readable code.

Interrupts

slides are really detailed about this and good - read them

call/return stack

31 level call/return stack. program counter preserved upon the calll instruction or interrupt. registers are not preserved - be careful not to clobber your registers.

simulation picoblaze assembly simulators exist - > prove your code by hand (slow) nothing stopping you from simulating the HDL design - but can be very slow. quicker to fix hardware design -> then code and download to picoblaze via jtag and run the software.

other picoblaze ide/assemblers/simulators/implementations that are not from xilinx

  1. pacoblaze Pacoblaze opensource, picoblaze compliant verilog implementation. complete with java assembler.
  2. openPicIDE openPicIDE opensource picoblaze ide/assembler/simulator. very robust! works on linux, mac, windows.
  3. mediatronix picoblaze ide mediatronix amazing windows picoblaze ide
  4. kpicosim kpicosim picoblaze simulator and assembler. linux