5.25" PROM Code Question

["Bryan Parkoff" <BParkoff@satx.rr.com>]

    I dump 5.25" Drive's PROM code into filename.  Please take a look below.
Please tell me what is this?  I have noticed that it uses too much loops
over and over before it begins to read track 0 and sector 0.  Why is loop
necessary?  What is the loop use for?

C600: A2 20        LDX #20
C602: A0 00        LDY #00
C604: A2 03        LDX #03
C606: 86 3C        STX 3C
C608: 8A           TXA
C609: 0A           ASL
C60A: 24 3C        BIT 3C
C60C: F0 10        BEQ C61E {+10}
C60E: 05 3C        ORA 3C
C610: 49 FF        EOR #FF
C612: 29 7E        AND #7E
C614: B0 08        BCS C61E {+08}
C616: 4A           LSR
C617: D0 FB        BNE C614 {-05}
C619: 98           TYA
C61A: 9D 56 03     STA 0356,X
C61D: C8           INY
C61E: E8           INX
C61F: 10 E5        BPL C606 {-1B}
C621: 20 58 FF     JSR FF58


--
Yours Truly,

Bryan Parkoff
BParkoff@satx.rr.com