Konami/ASCII mapper page switch latency

By Metalion

Paragon (1262)

Аватар пользователя Metalion

29-11-2020, 12:23


Is there any hardware latency that needs to be taken into account when switching page within a Konami/ASCII mapper ?

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By Grauw

Ascended (9498)

Аватар пользователя Grauw

29-11-2020, 13:24

There is no latency. The bank registers directly latch the value that is provided on the data bus. Latency implies a temporary buffer which is not present, there is no reason to buffer the value and wait before storing it in the registers. So they update immediately.

Hardware speed limitations are usually there due to some kind of time sharing mechanisms. For example, the FM chips use the circuitry for a single operator to produce the sound of all channels, so they need to buffer the value when it is written until the corresponding channel gets its turn. Another example, the VDP chips share the VRAM access with the CPU, so if the VDP needs access the CPU has to wait so the value written or read is buffered. Absent such a time sharing mechanism, things usually don’t require waits.

By thegeps

Hero (640)

Аватар пользователя thegeps

29-11-2020, 16:26

If you experienced some latency using a SD cartridge it is because the SD itself. I noticed some too when developing Freedom Fighter when switching ASCII16 banks. I was pretty sure that all was right because all went fine testing it in openMSX. Then I noticed that the latency occourred when the SD access led was on...

By gdx

Prophet (3924)

Аватар пользователя gdx

29-11-2020, 17:02

Original chips have no latency but it seems that some homemade mapper take a little time to switch page because I have seen megaroms modified just to add a small delay between pages switching.

By Metalion

Paragon (1262)

Аватар пользователя Metalion

29-11-2020, 19:04

No, I didn't experience latency, I was just curious to know if there was some that might need to be taken into account. Thanks everyone.