Black cat takes you to learn EMMC Protocol Part 24: detailed explanation of EMMC bus test program (cmd19 & cmd14)

This paper is based on eMMC JEDEC5.1 And personal work experience , If there is any mistake, please leave a message .
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1 summary

 Purpose
By means of SDR Issue command in rate mode CMD19 and CMD14, The host can detect device Which of them data The cable can work normally . For example, it detects emmc Of 8 root data The cable can work normally , After that host You can set and emmc Data line width of communication .

1、host send out cmd19 to device, Carry specified pattern The data of is in each selected data line .

2、host send out cmd14 to device,device Return the opposite pattern The data of .

Go through the above steps one by one , The function pins on the bus can be detected .

 The rules
The device will ignore all data bits except the first two bits of the data mode . therefore , In the device buffer The size of does not limit the maximum length of the data pattern . Although there are no restrictions on sending data pattern What is the longest length , But for sending data pattern The minimum length is specified , At least for 2 Byte. The first two bits of each data line are sent by the device in reverse to host.host Send to device Of data pattern You can choose to include CRC16 checksum, You can also exclude , Anyway device Will be ignored .