HW SPI support for ESP32

[MrSurly]

esp32/Makefile: Added hw spi object files
esp32/mpconfigport: Updated for hw spi
esp32/machine_hw_spi.c: New source file for hw SPI
esp32/machine_hw_spi.h: New source file for hw SPI

Squashed commit of the following:

commit 43ae202
Author: Eric Poulsen eric@zyxod.com
Date: Mon Apr 3 12:57:25 2017 -0700

esp32/README.md: merged with upstream

commit 57ce050
Author: Eric Poulsen eric@zyxod.com
Date: Mon Apr 3 12:44:50 2017 -0700

esp32/mahine_hw.*: copyright, reorg, now de-init resets pins to GPIO

commit 624a23c
Author: Eric Poulsen eric@zyxod.com
Date: Mon Apr 3 10:29:41 2017 -0700

esp32/Makefile: reverted FLASH_MODE to qio

commit c6af5a7
Author: Eric Poulsen eric@zyxod.com
Date: Fri Mar 31 12:12:20 2017 -0700

esp32/machine_hw_spi.*: Updated to make spi_obj.init(...) idiom work

commit d0c792c
Author: Eric Poulsen eric@zyxod.com
Date: Fri Mar 31 12:11:53 2017 -0700

esp32/Makefile: removed redundant object files

commit d3ecc01
Author: Eric Poulsen eric@zyxod.com
Date: Fri Mar 31 12:10:54 2017 -0700

extmod/machine_spi.c: reverted

commit 28cfb89
Author: Eric Poulsen eric@zyxod.com
Date: Fri Mar 31 11:03:50 2017 -0700

esp32/machine_hw_spi.*: temporary delete to fix merging

commit 92129b5
Author: Eric Poulsen eric@zyxod.com
Date: Fri Mar 31 11:01:17 2017 -0700

esp32/Makefile: updates for hw spi

commit c046e4f
Author: Eric Poulsen eric@zyxod.com
Date: Fri Mar 31 10:55:51 2017 -0700

esp32/machine_hw_spi.*: Renamed internals from hspi --> hw_spi

commit e0609a4
Author: Eric Poulsen eric@zyxod.com
Date: Fri Mar 31 07:45:47 2017 -0700

esp32/machine_hspi.*: Renamed to machine_hw_spi.*

commit 192a032
Author: Eric Poulsen eric@zyxod.com
Date: Thu Mar 30 14:55:12 2017 -0700

esp32/machine_hspi.c: Adding HW SPI support
esp32/machine_hspi.h: Adding HW SPI support

commit f41a01a
Author: Eric Poulsen eric@zyxod.com
Date: Thu Mar 30 14:54:31 2017 -0700

esp32/mpconfigport.h: Added support for HSPI

commit 0ec1d9e
Author: Eric Poulsen eric@zyxod.com
Date: Mon Mar 27 10:09:10 2017 -0700

esp32/README.md Added troubleshooting section to the end

[dpgeorge]

I tried it and it worked for me, except I couldn't change the baudrate once it was already initialised, but I guess that's a bug in the IDF.

A few comments re the code:

• move the typedef of the machine_hw_spi_obj_t struct from machine_hw_spi.h to machine_hw_spi.c (for type privacy)
• remove machine_hw_spi.h completely and put anything remaining in it into modmachine.h
• error message strings should start with a lower case letter
• remove trailing whitespace on lines
• make sure there is one space after the if/while/for keyword

Thanks!

[MrSurly]

I realized I screwed up by merging my branch back into esp32 prematurely.

I'm going to close this, fix up my branch w/ your recommendations, and re-submit a PR from that branch.

[MrSurly]

error message strings should start with a lower case letter

Didn't understand this one ... You mean the actual error message?

[dpgeorge]

You mean the actual error message?

Yes, eg "peripheral already in use" (not "Peripheral already in use", unless the first word is an acronym, eg SPI).