The purpose of this repository is to store machine-readable tables of instruction timings for various microcontrollers and CPU microarchitectures based on the 8051 (MCS-51) instruction set. These tables can be used for compiler optimization, predicting code performance, comparing how different 8051 microarchitectures might perform when executing the same code, identifying the specific microarchitecture being used in a particular 8051 microcontroller, and more.
Cycle timing tables are named based on the following format:
cycles_NAME_{measured,published}.csv
Where NAME is the name of the microcontroller or microarchitecture the table
contains cycle timing information for, and the last part of the filename
indicates whether the results were measured from a real chip or were derived
from published specifications.
This repository also contains a mapping between instruction mnemonics and
their instruction byte, the corresponding byte mask, and the number of bytes
used by that instruction (including the instruction byte). This mapping can be
found in opcode_map.csv.
The format of the cycle time tables is very simple. The format is CSV, using
commas as column delimiters and newlines as row delimiters. The first line is
the header and contains the column names, opcode and cycles. Each of the
following lines contains the masked instruction byte (or "opcode") of a
particular instruction in the left column, and the number of clock cycles
required to execute that instruction in the right column.
Not all valid instructions may be present in a table. For example, as the
RETI instruction can be difficult to measure the timing of accurately, it is
not present in any of the tables of measured cycle times in this repository.
Like the cycle time tables, the opcode map is also a CSV with
commas to delimit columns and newlines to delimit rows. Unlike the opcode map,
however, the header row contains the following column names: mnemonic,
opcode, mask, and bytes. The mnemonic is a text string (sometimes
quoted) containing the name of the instruction and its arguments. Like the
cycle time tables, the opcode is the masked instruction byte (or "opcode")
of the instruction described by the mnemonic. The mask is the bit mask
used along with the opcode to uniquely identify an instruction, since some
instructions (like ACALL, AJMP, DEC Rn, or MOV @Ri,#data) store some
or all of their arguments in some of the bits in the instruction byte.
Finally, the bytes column contains the count of the total number of bytes
occupied by that instruction. This count includes the instruction byte, so it
is always greater than or equal to 1.
Except where indicated otherwise, the contents of this repository are licensed under the Creative Commons Zero Public Domain Dedication.