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+++ b/se_k200i/README	Sun Nov 06 01:13:43 2022 +0000
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+In 2022-10 Vadim Yanitskiy discovered the existence of a previously unknown
+family of Calypso phones: Sony Ericsson K200/K220, usually with 'i' suffix.
+The only diff between K200 and K220 appears to be the FM radio receiver
+(present on K220, unpopulated PCB footprints on K200), whereas the suffix letter
+indicates GSM frequency bands: 'i' for 900+1800 MHz, 'a' for 850+1900 MHz.
+
+As of this writing (early 2022-11) Vadim and steve-m appear to be working on
+adding support for this phone model to their beloved pet OsmocomBB.  In
+contrast, I (Mother Mychaela) currently have no plans to add support for this
+phone model to FreeCalypso fw: it is not an interesting target for the purpose
+of turning it into a liberated end user phone by way of FC fw (for one thing,
+K200a or K220a phones with North American frequency bands appear to be
+unobtainium), and we don't need yet another alien phone running voice
+pseudo-modem firmware.
+
+However, I am gathering some notes about K200/220 hw and original fw in this
+directory, for two reasons:
+
+1) To provide better guidance to Vadim in his quest to support this weird phone
+   model in his beloved pet project;
+
+2) To gather knowledge in case the situation changes and a use case does arise
+   for porting our FreeCalypso fw to this target.
+
+If anyone does fancy the idea of running FreeCalypso fw on these SE K200/220
+phones, even if only as an experiment, the primary pain points will be mostly
+the same as with any other alien phone:
+
+* Like with almost every other alien Calypso device (phone or modem), the FFS
+  maintained by the original fw is not directly suitable as-is for FreeCalypso,
+  i.e., sharing the same FFS between original fw and FC, freely going back and
+  forth in fw with the same FFS, would be a bad idea.  Therefore, we would have
+  to decide whether to put our own FFS (with different content) in the same
+  sectors as the original, perhaps even produced from the original with our FFS
+  editor tool, or to put our aftermarket fw FFS in some other sector location.
+
+* In the case of Pirelli DP-L10 we were lucky to find an area of flash which
+  the original fw leaves unused and untouched in the vast majority of use cases
+  (staging area for OTA fw updates, unused at all other times), thus we could
+  put our separate-from-original FFS instance there.  This separate FFS
+  arrangement is what allows our FC fw on the Pirelli to be run via fc-xram,
+  without flashing.  But we don't have the same luck on K200/220: looking at
+  flash dumps, there does not appear to be any area that is totally unused and
+  could be repurposed for aftermarket fw FFS without disturbing the original fw.
+  Therefore, we won't have the option of non-invasive run-from-RAM operation,
+  and we would have to flash our fw instead, like on Mot C1xx.
+
+* The requirement of having to flash our fw, as opposed to running from RAM,
+  combines badly with the lack of phone UI functionality in voice pseudo-modem
+  fw: a phone that appears completely dead to the user but speaks some special
+  binary protocol on the UART when you press the PWON button feels extremely
+  weird and unnatural.
+
+* Having to flash our fw also means that we would need to either implement
+  battery charging in our fw (requiring thorough reverse eng of charging
+  specifics on this model) or use another phone (running original fw) to charge
+  batteries, moving batteries back and forth between phones.
+
+All of the above factors, which apply to *any* alien (meaning not FC-made) phone
+model, should make it clear why running our fw on alien Calypso phones is no
+longer the direction of interest in FreeCalypso - instead we need to focus on
+our own FreeCalypso hardware with phone handset functionality, starting with
+FC Venus.