CALCULATORS / EMBEDDED TIMING AND DIGITAL SYSTEMS

SPI transaction throughput calculator

Single SPI transaction including supplied overhead bits.

embedded-spi-throughput.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	durations	payloadRates^-1
	0.000144	888889
	0.00018	711111

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

transaction time budget144.00 us✓ passes

BASELINE INPUTS

clock1000000 HzpayloadBits128 overheadBits16

CALCULATED

duration0.000144 s

payloadRate888890 s^-1

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# SPI transaction throughput
# Scope: Single SPI transaction including supplied overhead bits.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

clock = 1000000 Hz
payloadBits = 128
overheadBits = 16

duration := (payloadBits+overheadBits)/clock [s]
payloadRate := payloadBits/duration [s^-1]

check transaction time budget: duration <= 200 us

scenario alternative: clock = 800000 Hz

Calculated from your source · not saved

Baseline · Baseline

transaction time budget144.00 us ✓ passes

alternative · alternative

transaction time budget180.00 us ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

duration: duration = (payloadBits+overheadBits)/clock [s]
payload rate: payloadRate = payloadBits/duration [s^-1]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

clock: 1000000 Hz
payload bits: 128
overhead bits: 16

Calculated

duration: 0.000144 s
payload rate: 888889 s^-1

Assumptions and limits

Single SPI transaction including supplied overhead bits.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: SPI transaction throughput. Inputs: clock; payload; overhead; inter-transaction delay. Outputs: effective payload rate; transaction time. Model scope: Declared clock, peripheral and execution assumptions. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: clock, payload, overhead, inter-transaction delay
Outputs: effective payload rate, transaction time
Modes: calculate, compare, sweep
Drawing: Timing diagram or event simulation

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS