View source for FPGAWorkshop13notes

''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 '''C'''oded '''P'''rogrammable '''S'''tate '''M'''achine

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

pointers available

'''port access'''

input and output ports available.

very simple with the two cycle operation
#1st cycle - instruction decode
#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'''

#blank lines are ignored
#comments begin with ;
#registers - form sX, where X={0,1,2,..9,A,...,E,F}
#constants
#Data value - 00 ->FF
#Port value - 00 ->FF
#Address - 000 ->3FF
#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'''

#'''pacoblaze''' [http://www.bleyer.org/pacoblaze/ Pacoblaze] opensource, picoblaze compliant verilog implementation.  complete with java assembler.
#'''openPicIDE''' [http://www.openpicide.org/ openPicIDE] opensource picoblaze ide/assembler/simulator.  very robust!  works on linux, mac, windows.
#'''mediatronix picoblaze ide''' [http://www.mediatronix.com/tools/index.htm mediatronix] amazing windows picoblaze ide
#'''kpicosim''' [http://www.xs4all.nl/~marksix/ kpicosim] picoblaze simulator and assembler.  linux