Follow Along Logic Analyzer
An asynchronous logic analyzer that triggers each time bus syntax is run from the terminal. It eliminates the need setup triggers and arm a second tool for debugging. We like to call it FALA for short.
The Bus Pirate can be used as a logic analyzer in multiple ways. This is the documentation for the "follow along logic analyzer" interface.
All Bus Pirate hardware supports follow along logic analyzer, however only Bus Pirate 6 has a second buffer to capture pins directly. In earlier hardware all output pins are measured behind the IO buffer. This means the logic capture may not match the actual output of the IO buffer. This is not a problem when the Bus Pirate is used as a logic analyzer only and all pins are inputs.
Capabilities
- 62.5MSPS (or more if overclocked)
- 131K samples
- 8 channels
- Trigger: single pin, high or low
- Follow along logic analyzer mode
- Base pin can be set to an internal pin for debugging the Bus Pirate itself
Enable FALA Interface
Select binary mode
1. SUMP logic analyzer
2. Binmode test framework
3. Arduino CH32V003 SWIO
4. Follow along logic analyzer
x. Exit
> 4
Binmode selected: Follow along logic analyzer
HiZ>
Enable the FALA binary interface with the binmode command. This will configure the logic analyzer and send capture notifications to the Bus Pirate's second serial port.
Auto Capture Speed
Logic analyzer speed: 80000Hz (8x oversampling)
Use the 'logic' command to change capture settings
Mode: SPI
SPI>
When changing protocol modes with the m command, FALA will automatically set the capture speed to oversample the bus speed by a factor of 8.
Change Capture Speed
Oversample rate set to: 16
Logic Analyzer settings
Oversample rate: 16
Sample frequency: 10000Hz
Note: oversample rate is not 1
Actual sample frequency: 160000Hz (16 * 10000Hz)
SPI>
The base capture speed or the oversample rate can can be changed with the logic command. Changing the oversample rate with the -o flag is probably easiest as the Bus Pirate will calculate the new sample frequency for you.
Capture Samples
CS Enabled
TX: 0xAA 0x55
CS Disabled
Logic analyzer: 144 samples captured
SPI>
Every time you send data to the bus, the logic analyzer will capture samples. The capture notification will be sent to the second serial port.
Protocol
There is currently no software support for FALA. The protocol is a work in progress. The GusmanB logic analyzer software has come a long way, and it supports asynchronous capture notifications. The current protocol may change to use the GusmanB protocol.
Asynchronous Capture Notification
$FALADATA,8,0,0,N,40000,168,0\n
Data arrives asynchronously, like GPS NMEA packets, so we structured notifications in a similar way. The notification is a string of comma separated values with the following fields:
- $FALADATA - Notification header
- capture pins (ex: 8)
- trigger pin mask (ex: 10100000)
- trigger mask (ex: 10000000)
- edge trigger (Y/N)
- capture speed in hz
- samples captured
- number of samples captured before the trigger (for pre-capture)
- terminated with a new line (\n)
Most languages can easily parse CSV.
+ - Dump Samples
+- Dump samples
In response to a capture notification, the host can request the samples with the + command.
Data format is a binary blob. Sample order is "backwards" with the newest sample first, oldest sample last.
? - Request Status
?- Request status
Returns the most recent capture notification. Can be used to retrieve missed capture notifications, or to check if the interface is active.
Logic Analyzer System
The logic command and the follow along binmode interface can be run at the same time. However, the capture buffer is shared with SUMP logic analyzer mode. SUMP and follow along logic analyzer modes cannot be used at the same time and will result in a memory error warning.