@rogloh said:
Same driver, different SD cards on different IO cmd/clk/data pins, right? Not actually sharing the same SD data bus (which I believe is theoretically possible in SD transfer mode); as that case seems like too much complexity.
Yes, two separate SD pins sets for two separate cards. That's how it is right now too. I have your Eval add-on uSD board at basepin 16 and a hand wired full sized SD slot I made at basepin 40.
The driver has no support for sharing the SD bus. It never deselects the card. EDIT: Err, it has to deselect to perform a CMD10 (SEND_CID) when it runs a rxlag calibration cycle.
On that note, I'd very much like to come up with a solution for using block reads instead of CMD10 to do the calibration with. The problem is there's no way to be sure the data blocks being read aren't just all zeros or all ones. I think I'd need to write data to the card storage.
@evanh said:
On that note, I'd very much like to come up with a solution for using block reads instead of CMD10 to do the calibration with. The problem is there's no way to be sure the data blocks being read aren't just all zeros or all ones. I think I'd need to write data to the card storage.
Oh, that's right, I did have an idea to attempt engaging 1.8 Volt UHS interface and see how the card handles the Prop2 staying 3.3 Volts ... if that somehow works then I can use UHS's dedicated CMD19 (SEND_TUNING_BLOCK) which uses the DAT pins.
EDIT: Nah, it'll be a bust. The Vdd supply stays at 3.3 V after UHS switchover. Which means, at the very least, the card's signalling will be too low for the Prop2 inputs at speed.
Comments
Yes, two separate SD pins sets for two separate cards. That's how it is right now too. I have your Eval add-on uSD board at basepin 16 and a hand wired full sized SD slot I made at basepin 40.
The driver has no support for sharing the SD bus. It never deselects the card. EDIT: Err, it has to deselect to perform a CMD10 (SEND_CID) when it runs a rxlag calibration cycle.
On that note, I'd very much like to come up with a solution for using block reads instead of CMD10 to do the calibration with. The problem is there's no way to be sure the data blocks being read aren't just all zeros or all ones. I think I'd need to write data to the card storage.
Oh, that's right, I did have an idea to attempt engaging 1.8 Volt UHS interface and see how the card handles the Prop2 staying 3.3 Volts ... if that somehow works then I can use UHS's dedicated CMD19 (SEND_TUNING_BLOCK) which uses the DAT pins.
EDIT: Nah, it'll be a bust. The Vdd supply stays at 3.3 V after UHS switchover. Which means, at the very least, the card's signalling will be too low for the Prop2 inputs at speed.