OK, forgive me, but I'm *really* confused between something specifically mentioned in the datasheet for the i.MX RT106x series SoCs, and something asserted here. I'm not arguing, and I want to be clear about that -- I don't know enough to argue -- but I'm having some cognitive dissonance because these two things seem mutually exclusive to me.
(1) from the datasheet (
https://www.nxp.com/docs/en/nxp/data-sheets/IMXRT1060CEC.pdf)...
Page 2:
The SoC-level memory system consists of the following additional components:
[...]
* External Memory Interfaces:
- 8/16-bit SDRAM, up to SDRAM-133/SDRAM-166
- 8/16-bit SLC NAND FLASH, with ECC handled in software
- SD/eMMC
- SPI NOR/NAND FLASH
- Parallel NOR FLASH with XIP support
- Two single/dual channel Quad SPI FLASH with XIP support
The first sounds to me like PC-133 SDRAM like you'd find in an old Win98 box. The second sounds a bit like a controllerless SSD. The third is pretty self-explanatory, as is the fourth. The fifth sounds a bit like an old SmartMedia card (I have a few for my Rio500 MP3 player... I love older electronics like that
), and the sixth sounds like one of the two chips for which there's a footprint on the underside of the Teensy, the other being a PSRAM that probably acts similarly enough to fool the SoC into thinking it's a second chip of the same sort (SPI Flash NVRAM) even though it's technically not.
But that distinctly sounds to me, since it explicitly states that these are *external* *memory* *interfaces*, like there's an MMU in there somewhere.
Further muddling things up is the absolutely useless "block diagram" on Page 9 of the datasheet, which looks like someone said "we *have* to have a block diagram" and the replies were "heck no we don't" followed by "you'll be sorry" followed by "we warned you"
it's three columns (and one row, at the very bottom) of boxes with category headers and none of it explains what's linked to what how. It's not even pretty to look at! But the eMMC / SD interface is listed under "Connectivity" and there's an "External Memory" category which lists "Dual-channel Quad SPI" and "Octal/Hyper Flash/RAM x2" in one box, and mentions an "External Memory Controller" with "8 bit / 16 bit SDRAM" "Parallel NOR Flash" "NAND FLASH" and "PSRAM" interfaces in another. I'm amused to notice that the PSRAM interface is mentioned here but not on Page 2. Interesting...
On Pages 10-16, there's a table that lists and explains various "modules" within the SoC... the last entry on Page 14 (but by no means last in the whole list!) is for the "SEMC" module -- the "Smart External Memory Controller". While this once again omits mention of PSRAM, there is another interesting addition, at the end of its description: "[...] as well as 8080 display interface."
Hmm... the 8080 was a CPU, of course, the one in the famous Altair 8800 and IMSAI 8080 (hellooooo "Wargames"!) computers, as well as many later S-100 bus machines, at least until the Z80 (which was based on it) came out. But that was the 8-bit era and *those* CPUs are *very* different creatures indeed. (Ironically, they're ones I understand pretty well... especially the 6502...). While there were a number of "display interface" types of chips, most of them were timing controllers -- what back then was called a "CRT Controller" ("CRTC" for short). Such chips required dedicated Video RAM but only sort of accessed it -- they would generate timing signals for a TV set or dedicated display-monitor, and spit out the relevant address signals to dump the contents of Video RAM into whatever support circuitry was in charge of feeding that to the screen and its analog boards proper. Probably the most popular such chip would've been the MC6845 from Motorola... in fact, as far as I'm aware, other than the *extremely* odd 8279 "Keyboard and Display Interface" (which is really for the sort of computer we'd now class as a hexadecimal trainer (think MOS Tech / Commodore KIM-1, or the Sinclair MK 14) -- it's designed to drive a hex keypad and a set of seven-segment LED digits, although the datasheet also "sort of" explains how to re-arrange the signals for the latter into use with a set of individual LEDs, should one desire that instead...), Intel themselves never released a display interface chip... although I have vague memories of coming across something somewhere, TBH, that mentioned both an MC6845 clone and another chip that was described as a "Small System CRT Controller" and sounded very much like a full-on VDG... except that it was basically never used! Apparently nobody bought it...
...but that's well off into the weeds, isn't it?
*ahem*
Can someone explain to me how this "external memory interface" is not a proper MMU?