It funny that you are talking about t3i/d4 cam , last night i was reading though my 5d2 rom disassembly
Looking for CF card udma string to set udma speed (e.g. udma6 5d2/50d to umda7 (120Mb) ) and Lossless stuff
I found the SD_SoftReset etc. ... all the stuff that you guy are playing around in the D5 Cams e.g. 700D etc. ... in the d4 rom
So the max speed in the rom for SD card is 48MHz plus there is a 24MHz mode also , not sure what speed the T3i records at ?
but I think it's doable to apply this code to t3i's if there not at max already , to be sure t3i can't go over 48MHz unless
the bus speed is over clocked . & Hi res crop_rec is only a matter of some one following what i did to the 50D .
It would be the same , i totally expect crop_rec to work on the t3i , but i don't have the time to do it my self (i will help thou

)
Any how found a couple of string for CF
ff38b1f8: STRING: 'cfIdentifyDrive: Set UDMA( Mode=%d )'
ff38b1b0: 128f20dc addne r2, pc, #220 ; *'CF_DeviceCreate: SoftReset
ffbdbb48: STRING: 'CF_GetAccessTiming : DatTim = %d, DatMod = %d'
I hoping to set CF to UDMA7 from 6 by code ,
I wondering are you able to set the band width when you are switch to hi-speed in the sd card on 700d ?
I see this in d4 rom
ff395544: STRING: 'SD_SetBusWidth: Width(Width=%d)'
ff395564: STRING: 'SD_SetBusWidth(CMD55)'
ff3955b0: STRING: 'SD_SetBusWidth(ACMD6)'
Also when over clocking to a higher speed dose the voltage increase to support the data output ?
Not sure how you would check that , it seems to me that same of the unstable results are some missing configuration or reg
my 2cents worth
Here a older (2001) Document on SD card I/O , nice read
http://ugweb.cs.ualberta.ca/~c274/resources/hardware/SDcards/SD_SDIO_specsv1.pdfGreat Work on this @theBilalFakhouri ,
Edit:
found this in the 700d 115 rom , i have
ff74aafc: e28f2e26 add r2, pc, #608 ; ff74ad64: (20746553) *"Set 1.8V Signaling"
ff74d684: e28f20fc add r2, pc, #252 ; ff74d788: (65536473) *"sdSendVoltageSwitch"
interesting ! i think the voltage for the older cards are around 3.3Vdc , or unless the newer cards use less voltage .
maybe other cam are having a voltage switching problem ? just a thought