Now that we can read SD cards and have an I/O interface in place from the Z80 to do I/O mapped access to the SD card it's time to hook the two pieces together. To do this we will need to look closer at how Grant's code request blocks. 

The loader code reads the status register SD_STATUS until the D7 bit is set.

The code then calls setLBAaddr. 

It the writes to SD_CONTROL with 0x00 which causes the block read.

0584   026E             ;================================================================================================
0585   026E             ; Read physical sector from host
0586   026E             ;================================================================================================
0587   026E             
0588   026E             readhst:
0589   026E F5                  PUSH     AF
0590   026F C5                  PUSH     BC
0591   0270 E5                  PUSH     HL
0592   0271             
0593   0271 DB 89       rdWait1: IN    A,(SD_STATUS)
0594   0273 FE 80               CP    128
0595   0275 20 FA               JR    NZ,rdWait1
0596   0277                     
0597   0277 CD 5E 02            CALL     setLBAaddr
0598   027A                     
0599   027A 3E 00               LD    A,$00    ; 00 = Read block
0600   027C D3 89               OUT    (SD_CONTROL),A
0601   027E             
0602   027E 0E 04               LD     c,4
0603   0280             ;        LD     HL,hstbuf
0604   0280             rd4secs:
0605   0280 06 80               LD     b,128
0606   0282             rdByte:
0607   0282             
0608   0282 DB 89       rdWait2: IN    A,(SD_STATUS)
0609   0284 FE E0               CP    224    ; Read byte waiting
0610   0286 20 FA               JR    NZ,rdWait2
0611   0288             
0612   0288 DB 88               IN    A,(SD_DATA)

Got it booting CP/M from the SD Card. 

Here's the SD card attached to the Z80_PSOC.

Hooray! 

Still need to get writes to the SD Card working.