WP34s&Co. - an internal flashdisk

[pito]

Quote:You could also put program memory in FRAM, but we're pretty liberal about large memory copies in the firmware. e.g. inserting a program step involves copying the rest of program memory to make space.

You may use the fram for user programs, and the arm's sram for the calculator's engine.

It is my understanding you interpret the user code, so reading a random step from fram may take several bytes, that could be done in 5-7useconds/byte via the 10-15MHz SPI, for example.

Reading ~30k user's program steps/sec from the external SPI fram seems to be a good deal provided the actual calculation runs in arm's sram (and takes ~msecs maybe).

Inserting a new step would mean copying (and r/w) of a larger chunk from fram to arm's sram and back - that shuffling could be done in up to ~1usec/byte (a typical 1kB large program can be loaded/stored in 1+1=2ms from/to the fram at above clock).

Imagine 256kB of a nonvolatile sram for user's programs in the wp34s (an $5 upgrade)..

PS: to clarify the weird numbers above:
The serial SPI SRAM/FRAM/MRAMs have an overhead related to the write/read operation, as you have to send the byte's address and commands before the actual write/read of respective byte. In order to write/read a single byte you have to transact 6/5 bytes via SPI bus, to write/read 1000bytes you have to transact 1005/1004 bytes (as the memories feature an "address auto-increment" from the initial address set).