Z80 CCF SCF Outcome Stability - redcode/Z80 GitHub Wiki

Platform: ZX Spectrum
Author: Helcmanovsky, Peter
License: MIT
Links: GitHub

Version Release date Links Download
v1.1 2022-02-17 GitHub commit tar.xz (hosted) - zip (GitHub)
v1.1 2022-02-02 GitHub commit tar.xz (hosted) - zip (GitHub)
v1.0 (hack) 2022-02-01 Discord post tap (hosted) - tap (Discord post)
v1.0 2022-02-01 GitHub commit, Discord post 1, Discord post 2 tar.xz, tap, trd (hosted) - zip (GitHub) - tap, trd.zip (Discord post)
alpha 2022-01-31 Discord post tap (hosted) - tap (Discord post)

Description

This tests stability of outcome of ccf/scf instructions, if the CPU does produce random values in flag register, the test will display red attribute square. For more details check the source comments.

This is near impossible to fail at FPGA or emulator, as it would need to add randomness intentionally, but some clones of Z80 CPUs in some machines do produce random values in undocumented flag bits (YF/XF), and this test can display whether the machine does produce random values at all, and whether it can be pinpointed to certain frame period like drawing PAPER area.

Nominal results

v1.1 v1.0 (hack)
v1.0 alpha

Results on real hardware

Zilog / ZX Spectrum +2A (ES, SN S039755)

Tested by ICEknight

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