AVR Freaks

The esp8266 uses external serial flash. Yes, you can write to it. You need to find out if thrme write speed is faster than the data you sample, otherwise a buffer will eventually fill. A common technique is the ‘ping pong’ where you have two buffers the size of the flash sector (4k methinks) . Whilst one buffer is being written, the other is being filled with data. The buffers are then swapped ie:ping pong.
Another technique is a fifo, maybe a circular buffer.
Note the esp8266 does not execute from flash - the code is loaded from flash into ram and executed. Thus the flash can be written at any time.

The flash is composed of a number of sectors of 4k each. You have to write a complete sector - not a byte at a time.

That assumes you have something connected via wifi. As well, I think the intention is not to use the AT command firmware.

You can keep it waiting by not writing the last byte (as declared by the <length> parameter), or by being automatically send when logged in upon return.

It seems you've biffed the design here, and you're lookig for a fix you can implement on your current platform.

I would suggest one or some of the following:

1. Reconfiguring the sensor to reduce it's sample rate enough to meet the 3min logging duration requirement.

2. Simply throw away 3 in every 4 samples. That'll get you to 4*50s (3½min).

3. Implement a data compression algorithm.

No 3. is by far the most difficult way but potentially the most fun to investigate. BTW: If you go this way; develop the code as a PC program with 3min  blocks of real data with the greatest variation you can achieve.

PS As I write this I'm listening to 192 kbit/s 48kHz audio (MPEG2) that originally would have been 1411.2 kbit/s  (2*16*44.1k).

Can I hear that there are missing bits ? Yes!

It it good enough for my purposes? Yes!

You can write to flash; but to achieve the desired rate you need to know:

1. The page buffer size
2. How quickly you can fill the buffer
3. How long a write cycle takes

If it were my design I might have included a serial EEPROM (24LC256 perhaps). So answering the above

1. The page buffer size = 32 bytes
2. How quickly you can fill the buffer = (5+32)*9 / 400kHz = approx. 1ms
3. How long a write cycle takes. = 5ms

Is there enough throughput ? At 6ms per 32 bytes - Yes there is plenty.

Edit

We're all inquisitive types here and I meant to ask:

What is the application?

What parameter must be sampled at 1ms intervals?

Does the linear actuator have a mink glove attached?

Try using F-RAM like this 128K byte IC on eBay:https://www.ebay.com/itm/5PCS-1M...

Feel free to post ESP8266 requests.  It is a companion processor to the AVR.  It is cheap and available.  AVR users integrate it into their designs more often than they mix with PICs, which is AVR's new stepsister CPU.

I’d question the use of an expensive fram when there’s a perfectly good 4MB serial flash available. As well, i’d skip the esp8266 and go the esp32- it’s a far superior part.