Tags

Looks like each tag is a null terminated short string. It looks like we don't do any compression for GHW format.

• Start ("GHDLwave")
• Strings ("STR" - "EOS")
• Types ("TYP")
• Known_Types ("WKT")
• Hierarchy ("HIE")
• End of header ("EOH")
• Snapshot ("SNP" - "ESN")
• Cycles ("CYC" - "ECY") ...
• Directory ("DIR")
  • Section Table (Name, Position), ...
  • End of directory "EOD"
• "TAI"

Simple Example GHW file's tags

GHDLwave STR EOS TYP WKT HIE EOH SNP ESN CYC ECY DIR STR TYP WKT HIE EOH SNP ESN CYC DIR EOD TAI

Sections

Header

Header Info

• Magic String (9 bytes): "GHDLwave\n"
• Header Info Length (1 byte): 16
• Major Version (1 byte): 0
• Minor Version (1 byte): 1
• Endianness (1 byte): 1 (Little Endian)
• Word Size (1 byte): 4
• File Offset Size (1 byte): 1
• Must Be Zero (1 byte): 0

Strings

• "STR" tag
• 4 NUL bytes
• 4 bytes string table length (number of strings)
• 4 bytes string length (sum of all string lengths)

string table entries

• 1 NUL byte
• "EOS" tag

String Table Entries

1. Copy prev_len characters from the last string to the beginning of your new string
2. Read characters into new string until you hit a non-printable character
3. prev_len = the non printable character (possibly with some bit manipulation)

Types

• "TYP" tag
• 4 NUL bytes
• 4 bytes type table length

Type table entries

• 1 NUL byte

Type Table Entry

Array

• 1 byte subtype array
• 1 NUL byte
• 4 bytes type ID
• 1 Byte Direction
• 1/4/8 Bytes Left
• 1/4/8 Bytes Right

Enum/Boolean

• 1 byte kind
• 4 byte string ID
• 4 byte number of values
• Value names

SubType Array

Snapshot

Dumps initial value of all signals

Cycle

Shows Signal value changes

Directory

This is a map of tags and their file offsets starting from STR and ending with DIR.