Crate jtag_taps

This crate allows for interacting with a JTAG test chain at a variety of levels of abstraction. At the lowest level, you can directly interact with a JTAG cable, such as those based on the “jtagkey” design. Other FT2232-based cables could easily be added, as well as direct GPIO control. The Cable trait allows for changing modes and shifting bits in and out of the JTAG chain.

The next higher level of abstraction is the JtagSM, which keeps track of the mode of the TAPs. You tell it which mode you want (e.g., Reset or Idle) and it gets there with the fewest number of mode changes. You can also read and write the instruction and data registers. read_write and write_reg take care of getting to ShiftDR or ShiftIR mode as appropriate.

If there are multiple TAPs in the JTAG chain, you probably want to use the methods associated with the Taps struct. You tell Taps how much TAPs exist and what the IR length is for each one. You can then read and write the instruction and data registers for that one TAP, and it will take care of putting other TAPs in BYPASS and shifting data in and out as appropriate. Taps also has some support for automatically detecting the IR lengths and ID codes of the TAPs.

Example

use jtag_taps::cable::jtagkey::JtagKey;
use jtag_taps::statemachine::JtagSM;
use jtag_taps::taps::Taps;
let cable = JtagKey::new("Dual RS232-HS A", 1 << 20);
let jtag = JtagSM::new(Box::new(cable));
let mut taps = Taps::new(jtag);
taps.detect();
 
let ir = vec![235, 0];
taps.select_tap(0, &ir);
let buf = vec![
    0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88,
];
taps.write_dr(&buf, 8);

Modules

• cable
  Implementations for different JTAG hardware adapters will here. Hardware adapters should implement the Cable trait.
• statemachine
  This provides a higher-level interface than the Cable trait. Specifically, it keeps track of the state of the JTAG state machine, and allows setting the state to any desired state. JtagSM will get to that state by the most efficient path, based on the current state.
• taps
  A convenience wrapper for JTAG scan chains with multiple TAPs present. Taps allows the client to interact with one selected TAP as if it were the only TAP in the chain, so that the client doesn’t have to deal with putting the other TAPs into bypass and shifting data through the bypass registers.