Using LPCxpresso with barebones LPC4337 board
Ok, I'd comment to you but now I try to answer to your question.

At first, Which compiler(or IDE) is better? keil or LPCxpresso?

It completely depends on your job and yourself. Well there are many features for each one of them. for LPCxpresso:


Complete C/C++ integrated development environment

Eclipse-based IDE with many ease-of-use enhancements
The IDE can be further enhanced with many Eclipse plugins
CVS source control built in; Git, Subversion, TFS, and others are
available for download
Command-line tools included for integration into build, test, and
manufacturing systems

Industry-standard GNU toolchain, including

C and C++ compilers, assembler, and linker
Converters for SREC, HEX, and binary

Fully featured debugger supporting JTAG and SWD

Built-in flash programming
High-level and instruction-level debug
Views of CPU registers and on-chip peripherals
Support for multiple devices on JTAG scan-chain

Library support

Redlib: a small-footprint embedded C library
Newlib: a complete C and C++ library
Cortex Microcontroller Software Interface Standard (CMSIS) libraries
and source code
Full support for LPCOpen libraries

Device-specific support for NXP's ARM-based MCUs (including
Cortex-M, ARM7, and ARM9 based parts)

Linker scripts automatically generated for correct placement of code
and data into flash and RAM
Startup code and device initialization provided
No assembler required with Cortex-M based MCUs

Red Trace

Red Trace enables instruction-level debugging via Embedded Trace
Buffer (ETB) or Micro Trace Buffer (MTB)

Red State state machine designer and code generator

Graphically design your state machines
Generates standard C code
Configures NXP State Configurable Timer (SCT) as well as supporting
software state machines



for Keil:


Feature The µVision Device Database automatically configures the development tools for the target microcontroller .:Benefit:. Mistakes in tool settings are practically eliminated and tool configuration time is minimized.
Feature The µVision IDE integrates additional third-party tools like VCS, CASE, and FLASH/Device Programming .:Benefit:. This allows you to quickly access all your development tools (development tools and third-party tools) from a single environment. All configuration details are saved in the µVision project.
Feature µVision incorporates project manager, editor, and debugger in a single environment .:Benefit:. Accelerates application development. While editing, you may configure debugger features. While debugging, you may make source code modifications.
Feature Identical Target Debugger and Simulator User Interface .:Benefit:. Shortens your learning curve.
Feature The Code Coverage feature of the µVision Simulator provides statistical analysis of your program's execution .:Benefit:. Safety-critical systems can be thoroughly tested and validated. Execution analysis reports can be viewed and printed for certification requirements.
Feature The µVision Simulator is the only debugger that completely simulates all on-chip peripherals of the Atmel, Philips, and Samsung smart card ARM devices .:Benefit:. This allows you to write and test application code before production hardware is available. You may investigate different hardware configurations to optimize the hardware design.
Feature Simulation capabilities may be expanded using the Advanced Simulation Interface (AGSI) .:Benefit:. Your sophisticated systems can be accurately simulated by adding your own peripheral drivers.


Also you can see the µVision Simulator Benefits here.

If you ask me about selecting the compiler, I want to choose the Keil because this company has a bigger and older experience in designing and making the IDEs and compilers and also I can see some disadvantages for LPCxpresso. for example seems it doesn't support non-NXP products (ST and TI and freescale and etc) and you cannot find many consultant and expert for speaking with them to figure out your problems. on the other hand, if you just want to use the NXP products then I think the LPCxpresso is better than the Keil.


  NXP has many examples of code, all of which have full drivers and everything. Normally that'd be awesome, although I want to write my own drivers since I want to know exactly what is going on with as little overhead as possible.


Why!? don't waste your time, Shannon! there are many HAL(Hardware Abstraction Layer (standard peripheral library)) that you can have a look at those and know exactly what is going on with as little overhead as possible. for example: the HAL library of company of your MCU or CMSIS or MBED.org lib and or etc.

a recommendation for choosing compiler:

if you have enough money, you can buy IAR(IAR Embedded Workbench for ARM) from IAR Systems. I have heared that it's the best compiler but you have to have enough skill for working with it.

I hope this will help you. if you still have any question, then ask in comment and if my knowledge is enough, I will answer you.

refrence:

Keil Wikipage

Advantages of the µVision IDE for ARM

Advantages of the µVision Simulator for ARM

LPCXpresso home

Mbed