- Sat Sep 06, 2014 7:29 pm
Ok, large part of relevant discussion happened in "Firmware Dump" thread: viewtopic.php?f=6&t=39
(and irrelevant discussion on SPI speed happened here - gotta love forums!). Anyway, based on analysis of external FlashROM dump provided there, and builtin ROM dump provided here, following conclusions can be made aboute the memory map:
0x40000000 (64K) - ESP8266 builtin ROM. It appears to be truly builtin, as its content doesn't appear in external FlashROM dump. The ROM technology is unclear. It can be mask ROM, or OTP, or just flash ROM whose means of programming are yet to be discovered. As more dumps for different modules will be collected, we'll be able to differentiate these choices.
0x40240000 - at this address irom0_0_seg memory segment is located, which in turn consists of .irom0.text sections, which are used in static libraries as provided in esp_iot_sdk_v0.6.zip . Data for this segment is contained at offset 0x40000 in external FlashROM. However, if you match memory map address and offset, it drags you to do some leap of faith and just tell:
0x40200000 - at this address, external SPI flash in mapped, unconfirmed. In particular, at 0x40240000 there's irom0_0_seg which contains library routines from SDK. At 0x40200000 there would be user application, but it is actually:
0x40100000 - User application from 0x40200000 gets shadowed here, which is Instruction RAM (size 32K). Shadowing supposedly happens for speed (and to be able to override interrupt vectors).
Risks and challenges:
1. All this information is based on the dumps provided by 3rd parties. They may be incorrect or erronuous.
2. kongo, provider of builtin ROM dump, reports that reading 0x40200000 and up returns zeroes (but then who are you to read my app? ever heard of vendor flash protection?)
3. Demo app from SDK was built and posted here, and sizes more than 32K, and thus won't fit into (provided by vendor) I-RAM size. But then it is surprisingly segfaults on execution.
4. FlashROM dump from 0x40000 doesn't contain nay ascii string, which is highly suspicious.
5. Other people bring in MMUs, unicorns, and dragons into the picture. But that apparently only makes Occam laugh.
Last edited by obvy on Sat Sep 06, 2014 7:50 pm, edited 1 time in total.