Hi I'm trying to understand requirements for switching Vmmc and Vqmmc supply voltages of SD cards. IIUC, Vmmc is the card supply voltage, applied to the card's VDD pin, Vqmmc is the voltage, used to pull up signal lines. Traditionally it used to be the same voltage, respectively, OCR reflects _the_ voltages, that cards support. Both voltages also would normally be supplied by one regulator, so, applied and removed "simultaneously." Now this changes with UHS SD cards, which require 1.8V Vqmmc and 3.3V Vmmc for high-speed operation. The SDHCI driver provides a reasonable example of the run-time power-supply management. I've also looked at the SD simplified physical layer spec (part 1) final version 3.01. But, I still have (at least) one question: what is the correct way to bring up the two regulators - Vmmc and Vqmmc in a generic case? I.e., if they really are provided by two separate regulators? Arguably, this isn't a very safe (or even compliant) design. Probably, you would supply Vqmmc from Vmmc too, in which case "enabling" Vqmmc first should be safe, but what if those are really two independent regulators? If we power Vmmc first we risk random garbage on data lines... So, looks like we really have to enable Vqmmc first and just hope that this really won't apply power to the pins before Vmmc is also switched on? Or should cards be able to handle Vqmmc on with Vmmc off? Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
