The dwMaximumClock field is a number value from the USB CCID descriptor:
Maximum supported ICC clock frequency in KHz. This is an integer value.
Example: 14.32 MHz is encoded as the integer value 14320. (000037F0h)
| dwMaximumClock | # | % |
|---|---|---|
| 4.000 MHz | 94 | 37.01 % |
| 8.000 MHz | 43 | 16.93 % |
| 3.580 MHz | 33 | 12.99 % |
| 12.000 MHz | 17 | 6.69 % |
| 3.700 MHz | 10 | 3.94 % |
| 4.800 MHz | 10 | 3.94 % |
| 13.560 MHz | 8 | 3.15 % |
| 7.500 MHz | 6 | 2.36 % |
| 4.615 MHz | 5 | 1.97 % |
| 1.500 MHz | 4 | 1.57 % |
| 20.000 MHz | 3 | 1.18 % |
| 3.570 MHz | 3 | 1.18 % |
| 3.600 MHz | 3 | 1.18 % |
| 1.000 MHz | 2 | 0.79 % |
| 3.571 MHz | 2 | 0.79 % |
| 3.692 MHz | 2 | 0.79 % |
| 1024.000 MHz | 1 | 0.39 % |
| 16.000 MHz | 1 | 0.39 % |
| 2.000 MHz | 1 | 0.39 % |
| 3.000 MHz | 1 | 0.39 % |
| 3.685 MHz | 1 | 0.39 % |
| 3.686 MHz | 1 | 0.39 % |
| 3.850 MHz | 1 | 0.39 % |
| 4.714 MHz | 1 | 0.39 % |
| 5.000 MHz | 1 | 0.39 % |
We find nearly the same values as for dwDefaultClock (See CCID descriptor statistics: dwDefaultClock):
- 4.0 Mhz: (37% of readers), 48% of readers have a default clock of 4.0 Mhz
- 8.0 Mhz: (17%) this is just the double of a default clock of 4.0 Mhz
- 3.58 Mhz: (13%) same as default clock for 34 readers
- 12 Mhz: (7%) 3 times the default clock of 4.0 Mhz
The maximum clock speeds are more diverse than the default clock speeds.
If we draw the number of reader per clock frequency we have:
The value 1024 Mhz (1.024 GHz) is, here again, clearly from a bogus reader.
