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I2C Device Information Bank
This bank allows I2C Masters to interrogate the device and discern device properties. All registers in this bank are read-only.
Magic Bytes (Product Identification)
Addresses [0x000, 0x00f] form a known sequence so that I2C Masters can identify the device. The sixteen bytes have been generated as a
GUID and should not be taken as encoding any specific information other than being a sufficiently long pattern serving to identify this device from
a possible EEPROM or other device. In the event of the device being assigned an unknown I2C address, Masters should be able to discover
this device on the bus by iterating all possible I2C addresses looking for this sequence.
| 0x000 | 0x00f | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0xfb | 0xb0 | 0x90 | 0x7d | 0xdd | 0x09 | 0x47 | 0x74 | 0x8c | 0x31 | 0x7f | 0x71 | 0xf9 | 0x12 | 0xb9 | 0x2c |
Firmware Version
The version of the device firmware resides at [0x010, 0x013]:
| 0x010 | 0x013 | ||
|---|---|---|---|
rrrrrrrr |
mmmmmmmm |
MMMMMMMM |
ffffffff |
The version number follows the Semantic Versioning conventions of MMMMMMMM.mmmmmmmm.rrrrrrrr (major.minor.revision).
The ffffffff field is for flags. Currently these flags are all reserved and the byte should equal 0x00.
USB API Version
The API that is exposed to the USB Host is versioned separately to the overall firmware version. The version of the API resides at addresses [0x014, 0x017]:
| 0x014 | 0x017 | ||
|---|---|---|---|
bbbbbbbb |
BBBBBBBB |
mmmmmmmm |
MMMMMMMM |
The version number follows the Semantic Versioning conventions of MMMMMMMM.mmmmmmmm.00000000 (major.minor.revision) because
the USB Specification only provides two fields, so revision is always zero. The same version number is encoded as Binary Coded Decimal (BCD) by the fields
BBBBBBBB.bbbbbbbb, which is the representation used by the USB Device Descriptor.
MCU Device ID
The Microcontroller’s DEVID register is exposed at addresses [0x018, 0x01b]. According to the
PIC32MM0256GPM028 datasheet:
| 0x018 | 0x01b | ||
|---|---|---|---|
iiiiiiii |
iiiiiiii |
iiiiiiii |
vers iiii |
The Device ID bits (i) will form the word 0x07718053, whilst the four vers bits specify the silicon revision.
Unique Device ID
The Microcontroller’s five UDID* registers are exposed at addresses [0x01c, 0x02f]. These registers do encode die co-ordinate offsets and other
relatively unique parameters but the details are unimportant. Effectively these bytes provide a serial number, and because of this they are also
exposed via the USB’s Device / Serial Number String Descriptor:
| 0x01c | 0x01f | 0x020 | 0x023 | 0x024 | 0x027 | 0x028 | 0x02b | 0x02c | 0x02f | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
11111111 |
11111111 |
11111111 |
11111111 |
22222222 |
22222222 |
22222222 |
22222222 |
33333333 |
33333333 |
33333333 |
33333333 |
44444444 |
44444444 |
44444444 |
44444444 |
55555555 |
55555555 |
55555555 |
55555555 |
Where 1 is UDID1, 2 is UDID2, etc.
MCU Device Reset Reason
The Microcontroller’s RCON register is exposed at addresses [0x040, 0x043]. See the Device Reset Reasons page for more information.
MCU Exception Details
During some resets, snapshots of the Microcontroller’s ERROREPC, EPC, CAUSE, DESAVE and RA registers are exposed at addresseses [0x044, 0x054],
respectively. These values are useful for debugging.
At addresses [0x058, 0x05f] are two debugging words that are persisted across device resets that can be written by the firmware. In ordinary operation these
values are undefined (uninitialised), but they are useful for leaving traces and markers when hacking the firmware is causing hard-to-find general exceptions.