Yes, I need USB to allow reading of the recorded data by the PC.
In fact the full-speed USB is awfully slow for reading 1GB of data, but
anyway it may be more convenient, than repeated removing of the SD/MMC card
and puting it back (at least the user should have a choice).
The device must be as cheap as possible, and built from the easily available
(in EU, specifically in Poland) parts (therefore I wouldn't like to use
PIC32).

Maybe I'll stick at PIC18F4550 or 18F4553, implementing the bit banged SPI.
SPI is called synchronously when transmitting the data, so it is relatively
easy. I only have to assess the amount of cycles needed to transmit the
single byte.
I haved found the 40 instructions output only implementation:
http://www.piclist.org/techref/postbot.asp?by=time&id=piclist/2004/03/03/105839a

My best in/out implementation is 64 instruction long (8 instructions for
a single bit):

; set the clock line to 'L'
  bcf  clk_port, clk_pin,0
; move the highest bit to the carry, and 0 to the lowest bit
  addwf WREG,0,0
; set the data line to carry
  bcf   sdo_port,sdo_pin,0
  btfsc STATUS,0,0
  bsf   sdo_port,sdo_pin,0
; read the input pin
  btfsc sdi_port, sdi_pin,0
; set the bit 0 in WREG to SDI
  bsf  WREG,0,0
; set the clock line to 'H'
  bsf  clk_port, clk_pin, 0

When repeated 8 times (using "copy&paste" technique) this routine transmits
the byte located in the WREG, and replaces it with the byte received from
the SPI in 64 instructions.

Does anybody know how to improve it?

---

Regards,
Wojtek
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