Field-Programmable Oscilloscope (FPO) Logic Analyzer

This is FPgaOscilloscope or Field-Programmable Oscilloscope

FPO resides in FPGA along with the main project and allow to observe their signals. Only generic VGA monitor & ps/2 mouse and few resistors required to use. See connection schematic below.

Download without registration: https://github.com/zenlu/FPO

Motivation and Goal

FPO has designed for hard times, when another FPGA design produce "magical" behavior.

Generally it impractical or even impossible to use "real hardware oscilloscope" for debugging a bunch of internal FPGA signals (simulation may give fine results without problems because of simplified tests, and there is no reason to increase test set complexity (e.g. try to implement asynchronous & noisy external inputs))

Multi-channel and close to "FPGA guts" nature of FPO can successfully used in this situation.

Features

• Pure VHDL (no CPU core)
• 7 external pin requited (5 for VGA output, 2 for PS/2 mouse IO)
  +1 optional: reset (for load default values mainly)
• Wishbone compatibility: not applicable
• Separated clock domains for acquisition and VGA-forming
• (3 clock domains: data acquisition, VGA-forming, PS/2 interface)
• License: GPLv3

• Normal, Single, Stop modes
• Multi-channel: Each channel (line) has it own data type
• Implemented types:
  • Single bit
  • Bus trail chart
  • Analog-like chart: dot and bar style
• Configurable (excludable blocks) options:
  • Value indication (at cursor)
• Future (planned) extensions:
  • Hold-off (trigger)
  • Auto mode
  • DVI-D output
  • video data processor (when sample/pixel > 1)

Bugs/Limitations/Dubious features

• Run/Stop require double click to operate in SNGL mode
• Mouse data bounce sometimes

Thanks to:

VGA timing info get from : http://tinyvga.com

Font get from..,, Sorry, I don't remember

Contact

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Donations

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----- Details -----

Structure.

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Tips(How-to)

Hardware.

VHDL.

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Configuration Option Usage:

Copy fpocfg_pkg.vhd to your project directory and modify required parameters.,

CFG: fpo_config: fill list of desired traces. Available types:

• bit16 - plot 1 bit, trace height: 16.
• bus16w4 - plot 4 bit like 4 parallel separate trails each 2 pix height with 2 pix space, total height: 16.
• dot64u - 6 bit unsigned value plot as (unconnected) dot for each value, trace height 64.
• bar64u - 6 bit unsigned value plot as vertical strip (height=value), trace height: 64.
• bar256u - 8 bit unsigned value plot as vertical strip (height=value), trace height: 256.
• separ4 - horizontal separator for grouping traces, no bit plotted, height : 4.

CFG: traceval_enable : if true then value indication part will be included (if false then preserve FPGA resource)

CFG: drift_default, disp_default contain initial default values (loaded by means of reset) for correspondent working parameters. (see Parameter Explanation)

CFG: scale_default, trgmode_default, act_default contain default values (loaded by means of reset) for correspondent working state (see Brief Operators Manual)

CFG: depth_default contain total number of acquired samples-1 (per one working cycle) (see Parameter Explanation).

CFG: ramlength : contain maxim number of samples which may be acquired by given instance FPO (see Parameter Explanation).
Total acquisition RAM size (bits): 3*ramlength*(fpo_data_type'width)

Other files:,

CFG: filter in trigger_pkg.vhd: if true then flip-flop will applied first to trigger input signal. (recommended when trigger input signal is not synchronous to clk)

CFG: vbuf in graphics_pkg.vhd: if true then vc (vgaoutput) will be pipelines. Recommended: true. Experimental use only : if false then FPO performance test by direct observation artifacts on display.

Synthesizing Demo Tips

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Trigger.

Probing

GHDL

just run make and enjoy diagrams in GTKWave by opening test.vcd.

Brief Operators Manual

It simple intuitive 😊. Anyone who familiar with oscilloscopes is capable to use FPO.

Status line is string line (last bottom line with yellow chars typically) indicating values of FPO control parameters.

All values are expressed in (hexadecimal) number of acquire clocks.

• Scale: explicitly represent pixel per acquiring clock ratio used to output acquired data to screen, Example: PIX/CLK=2/1 mean 2 pixel is used to represent (plot) 1 clk period. (Zoom in toward 1/1)
• Drift: see Parameter Explanation
• Disp: see Parameter Explanation
• Mode:
  • Normal: as ordinary oscilloscope -- start acquisition by trigger event.
  • Single: as ordinary oscilloscope -- start acquisition by trigger once, manual restart required.
• FPO state Run/Ready/Stop/Fill:
  • Run: Acquiring samples to RAM after trigger.
  • Stop: Acquiring is stopped and will not start without manual intervention.
  • Ready: Ready to Run (buffer has prefilled), awaiting trigger or manual start.
  • Fill: Prefill samples (trigger prehistory acquisition)

Control cursor is red square movable (by mouse) horizontally along status line.

To change parameter value (drift, disp) move control cursor on value, then press and hold left mouse button and move mouse up/down to increment/decrement value.

To change selector (scale, mode, activity) move control cursor on corresponded indicated field and press left mouse button. Selector values are looped.

Activity selector: Start/Stop oscilloscope (or manual restart in single mode) associated with FPO state field.

Parameter Explanation

positive drift :
|<--------------ramlen--------------------------------->|
|                                                       |
|        |<---------depth------->|                      |
|        |                       |                      |
|        |        [ visible ]    |                      |
[========|========[  area   ]====|======================]
         |        [         ]
         |<-disp->|
         |           ^
         |<--drift-->E
                     ^
                     |
                  trigger (snap)
---time---->

• ramlen -- total RAM length
• depth = [0..ramlen-1] acquisition length (depth = 0 correspond to 1 sample, depth = n => n + 1 sample)
• disp = [0..depth] is offset of displayed (visible) area from acquisition beginning.
• drift = [-32768 to ramlen-1] is offset from the beginning of acquisition (to RAM) to the trigger (snap) pulse (negative value correspond trigger pulse before start of acquisition)

Connection Schematic

            ________________________________________                            ____________
           |                       _________________|                          |            |
           |      [DEMO]          |                 |          Rl ___          |     6      |
           |                      |      [FPO]      |          +-|___|----------o      |
 _______   |                      |                 |  Rh ___  |               | 1       11 |
|       |  |                      |            vc.r |----|___|-+-----------------o       o  |
|  OSC  |  |                      |                 |          Rl ___          |     7      |
|       |  |                      |                 |          +-|___|----------o      |
| 50MHz |-->--+-------------------> clk             |  Rh ___  |               | 2       12 |
|_______|  |  |   _____________   |            vc.g |----|___|-+-----------------o       o  |
           |  |  |             |  |                 |          Rl ___          |     8      |
           |  |  |   divider   |  |                 |          +-|___|----------o      |
           |  |  |             |  |                 |  Rh ___  |               | 3       13 |
           |  +--> clk         |  |            vc.b |----|___|-+-----------------o       o--------
           |  |  |             |  |                 |                          |     9      |    |
           |  |  |      acqena |--| ena             |                          |     o      |    |
           |  |  |_____________|  |                 |                          | 4       14 |    |
           |  |   _____________   |                 |                          | o       o------ |
           |  |  |             |  |                 |                          |     10     |  | |
           |  |  |   counter   |  |                 |                      ----------o      |  | |
           |  |  |    coder    |  |                 |                      |   | 5       15 |  | |
           |  |  |             |  |                 |               --+-----o       o  |  | |
           |  +--> clk         |  |                 |                          |____________|  | |
           |  |  |             |  |                 |  Rs ___                   VGA connector  | |
           |  |  |           q |==| d          vc.v |----|___|---------------------------------- |
           |  |  |_____________|  |                 |  Rs ___                                    |
           |  |                   |            vc.h |----|___|------------------------------------
           |  +-------------------> vclk            |                               _____
           |  |                   |                 |         Ru ___              _|     |_
           |  |       [LOG1]------| vena            |  <+3.3V>--|___|-+          |         |
           |  |                   |                 |                 | Rp ___   | 1     2 |
           |  +-------------------> ps2clk     ps2d |-----------------+---|___|----o     o |
           |  |   _____________   |                 |                            |         |
           |  |  |             |  |                 |                            |         |
           |  |  |   divider   |  |                 |                            | 3     4 |
           |  |  |             |  |                 |                     ----o  _  o----<+5V>
           |  +--> clk         |  |                 |         Ru ___             |   [ ]   |
           |     |             |  |                 |  <+3.3V>--|___|-+          |   [_]   |
           |     |      ps2ena |--| ps2ena          |                 | Rp ___   | 5     6 |
           |     |_____________|  |            ps2c |-----------------+---|___|----o  _  o |
           |                      |_________________|                            |___| |___|
           |________________________________________|                           PS/2 connector
                           FPGA IC

Voltage levels & pins IO standard: VGA & PS2 IO is configured to lvcmos 3.3v.

Rh + Rl is divider-terminator matching 75 Ohm color transmission line. May be selected from tables below. Rh can be reduced on about 20 Ohm because FPGA output driver has internal resistance. Suppose 141/161 pair is suitable for most cases.

       VGA 0.7 V
  IN  | Rl  | Rh  | CUR
  ----|-----|-----|----
  3.3 | 130 | 177 | 14.7
  3.0 | 141 | 161 | 14.3
  2.8 | 150 | 150 | 14.0

       VGA 1.0 V
  IN  | Rl  | Rh  | CUR
  ----|-----|-----|-----
  3.3 | 191 | 124 | 18.5
  3.2 | 200 | 120 | 18.3
  3.0 | 225 | 112 | 17.8
  2.7 | 300 | 100 | 16.7

Rs is series terminator for synchronization lines. Accurate impedance of this lines is unknown, suppose in range 60-120 Ohm. Rs about 60-80 Ohm should be fine.

Ru is pull-up for mouse lines. Ru = 2-4 kOhm should be fine.

Rp is kind of protection & spikes suppressor. Rp = 100-300 Ohm.