[sdiy] 32 bit RISC MIPS32 PICs in 28 pin DIP with audio codec interfaces & USB

[Robin Whittle]

From: Re: [sdiy] DECISION TIME: need a Ucontroller/ARM/DSP chip that
          will process audio
Hi Jay,

Thanks for pointing this out:

> These will be coming out in the next few weeks:
> http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en557433
> http://www.microchipdirect.com/ProductSearch.aspx?Keywords=PIC32MX250F128D

For instance, the 28 pin DIP PIC32MX150F128B (or D with 44 pins an TQFP
and QFN) has an SPI port which is apparently capable of talking
bidirectionally to a stereo DAC/ADC (AKA audio codec).  I haven't chased
the details, but page 165 of the datasheet states that it can do the I2S
protocol which is often used by codecs.  This port has FIFOs.

This chip of the series has the most program memory (128k bytes) and RAM
(32k bytes), and a 10 bit ADC.  They are available now for $3.70 in 1 to
25 quantities.  I guess there is a 44 pin version development header
board which could be used to develop for the 28 pin DIP version without
using any of the 28 pin DIP pins for the debugger connection.

The PIC32MX250F128x is similar, but has USB capabilities which I have
not looked at.

The CPU is 40MHz with single cycle 16 x 32 multiply and accumulate (MAC)
two cycle 32 x 32 MAC.  However, this is a RISC CPU so I wonder how long
it takes to calculate operand addresses and read the operands.  The
dsPIC CPUs are 16 bit but have this totally wired - they can steam ahead
doing a 16 bit MAC with all address calculations and reads and writes
pipelined, one per 40MHz clock cycle.

There's not enough pins for accessing external RAM in any simple and
high-speed manner.

The CPU design is a MIPS32 "M4K", but I think this is "4Km", licensed
from MIPS:

  http://www.mips.com/products/cores/32-64-bit-cores/mips32-4k/

Its amazing what will fit into a 28 pin DIP package.  I haven't looked
exhaustively, but as far as I know there are no 16 bit audio codecs in
DIP packages.  For field serviceability, a codec could be mounted in a
DIP header.

  - Robin      http://www.firstpr.com.au/rwi/dfish/