These tests primarily check that the bits aren't shorted, open,
or misrouted, and the the DTS overlay is properly configured.
Ensure that the ppdev module is loaded before running these
tests.
loop A utilizes a DB25 loopback plug wired as below.
| Pin | Name | Pin | Name |
|---|---|---|---|
| 3 | DATA1 | 14 | CONTROL1 |
| 4 | DATA2 | 15 | STATUS3 |
| 5 | DATA3 | 17 | CONTROL3 |
| 6 | DATA4 | 13 | STATUS4 |
| 7 | DATA5 | 12 | STATUS5 |
| 8 | DATA6 | 10 | STATUS6 |
| 9 | DATA7 | 11 | STATUS7 |
phase 1 DATA is configured for output. Each of 256 possible output values is placed in the DATA register, then the STATUS register is read. The bits from DATA[2,4:7] must appear on STATUS[3:7].
phase 2 DATA is configured for input. Each of 16 possible control values is placed in the CONTROL register, then the DATA register is read. The bits from CONTROL[1,3] must appear on DATA[1,3].
loop B utilizes a DB25 loopback plug wired as below.
It covers the pins missed by plug A.
| Pin | Name | Pin | Name |
|---|---|---|---|
| 2 | DATA0 | 1 | CONTROL0 |
| 4 | DATA2 | 16 | CONTROL2 |
DATA is configured for input. Each of 16 possible control values is placed in the CONTROL register, then the DATA register is read. The bits from CONTROL[0,2] must appear on DATA[0,2].
strobe pin [period] simply toggles a selected pin at a target period
so it can be scoped. This is useful for debugging if the loop tests fail.