The Hierarchical Scan Description Language (HSDL) was developed by to complement BSDL.

HSDL using the same subset of VHSIC Scan Description Language (VHDL) statements as BSDL.

BSDL focuses on describing only IEEE compliant devices.

It does not address IEEE at the board, system, or multi-chip module levels.

BSDL also needs a few device- level features added to better support interactive debug.

Manipulating test registers as a stream of bits is not easy, and determining the values on device pin buses or on fields within test data registers by looking at binary or hexadecimal output is impossible.

HSDL picks up where BSDL stops, describing additional attributes of IEEE devices and how IEEE devices are connected at the board and system level.

HSDL addresses a number of deficiencies in both BSDL and Configuration Files.

It supports all the features of BSDL for industry compatibility, providing support for automatic test-pattern generation, validation, and synthesis tools.

HSDL also supports all the convenience features of Configuration Files, providing the ability to describe boards, name subsets of test registers, create symbol tables for test registers or fields that use symbolic, named values, prevent illegal states from being established, and so forth.

For automated tools, HSDL includes new features such as those for describing different status values captured by a test register and designating them as "pass" or "fail" values.

For interactive use, HSDL includes new features such as those for adding descriptive text to each item in the entity.

HSDL is a strict superset of BSDL: All statements that are part of HSDL device entities but not part of BSDL are optional.

Thus, BSDL is an acceptable input to an HSDL translator!!!

HSDL device entities can be made acceptable to a BSDL translator simply by feeding them to the BSDL translator and deleting all the new statements that cause syntax errors, with no loss or change in meaning.

HSDL uses the BSDL entity and package in new ways: Entities in HSDL describe modules as well as devices.

(A module is any level of architecture above the device level, including boards, multichip modules, backplanes, subsystems, and systems.)

In addition, HSDL provides two new packages used to indicate that an entity is an HSDL device or module.

BSDL is great for describing how IEEE is implemented in a device, but stops there…

HSDL provides a method for describing how IEEE devices are connected at the board, module, and system levels!

HSDL module statements use much of the same syntax as BSDL.

New statements have been added to describe the members and scan paths of the module and to simplify interactive use.

HSDL employs the same subset of VHDL statements used by BSDL. However, the VHDL statements are used in more flexible ways in HSDL than in BSDL.

For example, BSDL only attaches attributes to the entity. HSDL attaches attributes to the entity, the ports, and to Symbol Table and Path constants.

These three different VHDL items are used in the same manner in HSDL as they are in BSDL.

HSDL has two types of entities, however: device entities and module entities.

A device entity describes an IEEE device, with test registers, instructions, and a TAP.

A module entity describes an IEEE module, which contains other device and module entities arranged along a scan path.

EXAMPLES…

ENTITY DESCRIPTION The entity statement names the entity, such as the module name (e.g., BOARD). An entity description begins with an entity statement and terminates with an end statement: entity BOARD is {statements to describe the entity go here} end BOARD;

GENERIC PARAMETER (Unchanged from BSDL) A generic parameter may come from outside the entity or it may be defaulted, such as a package type (e.g., "UNDEFINED"). generic (PHYSICAL_PIN_MAP : string := "UNDEFINED")

LOGICAL PORT DESCRIPTION (Unchanged from BSDL) T he port description gives logical names to the I/O pins (system and TAP pins), and denotes their nature such as input, output, bidirectional, and so on. port (TDI:in bit; TDO:out bit; TMS:in bit; TCK:in bit);

USE STATEMENTS The use statement refers to external definitions found in packages and package bodies. use STD_1149_1_1990.all; use HSDL_module.all;

PIN MAPPING(S) (Unchanged from BSDL) The pin mapping provides a mapping of logical signals onto the physical pins of a particular entity. attribute PIN_MAP of BOARD : entity is PHYSICAL_PIN_MAP; constant PINOUT1 : PIN_MAP_STRING := "TDI:1, TDO:2, TMS:3, TCK:4, GND:5";

SCAN PORT IDENTIFICATION (Unchanged from BSDL) The scan port identification statements define the entity's TAP. attribute TAP_SCAN_IN of TDI : signal is TRUE; attribute TAP_SCAN_OUT of TDO : signal is TRUE; attribute TAP_SCAN_MODE of TMS : signal is TRUE; attribute TAP_SCAN_CLOCK of TCK : signal is (5.0e6, LOW);

PATH DESCRIPTION Module paths are intended to describe the netlist of TAP signals (scan paths) on the board constant boardpath1 : STATIC_PATH := "U1, U2"; end BOARD;

And there are many more…