RFMicrocontroller Cross Compiler: A Comprehensive Guide
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A Microcontroller Cross Compiler is a program that translates source code written in a higher-level language (like C) into a lower-level language (assembly language/machine code/binary code/object code). This resulting object code is then suitable for execution on a specific target, such as a microcontroller or processor.
The primary reason for this conversion is to create an executable program tailored for the desired target device. When the target program is compiled and meant to run on a computer/platform/system with a CPU/operating system different from where the compiler itself is installed, this type of compiler is known as a cross-compiler.
Tools like µVision are widely used as compilers for various microcontroller families. µVision assists in the development and testing of embedded applications for ARM/Cortex-M, C166/C251/C51 microcontrollers.
The following memory type models, variable types, and Special Function Registers (SFRs) are used in 8051-based cross compilers.
Memory Types
The memory model dictates the default memory type to be used for:
- Function arguments
- Automatic variables
- Declarations lacking an explicit memory type specifier
You can specify the memory model on the Cx51 command line using SMALL, COMPACT, and LARGE directives.
| Memory Type | Description |
|---|---|
code | Program memory |
data | Directly addressable internal data memory |
idata | Indirectly addressable internal data memory |
bdata | Bit addressable internal data memory |
xdata | External data memory |
pdata | Paged external data memory |
Variable Data Types
| Variable data type | Bits | Bytes | Value Range |
|---|---|---|---|
bit | 1 | 1 | 0 to 1 |
signed char | 8 | 1 | -128 to +127 |
unsigned char | 8 | 1 | 0 to 255 |
signed short | 16 | 2 | -32768 to +32767 |
unsigned short | 16 | 2 | 0 to 65535 |
signed int | 16 | 2 | -32768 to +32767 |
unsigned long | 32 | 4 | 0 to 4294967295 |
float | 32 | 4 | +/- 1.17E-38 to +/-3.40E+38 |
sbit | 1 | 1 | 0 to 1 |
sfr | 8 | 1 | 0 to 255 |
Special Function Registers (SFRs)
Intel 8051 family microprocessors designate a specific memory area for accessing SFRs. SFRs are primarily used to control timers/counters, serial I/Os, port I/Os, and other peripherals.
SFRs are addressed from 0x80 to 0xFF and can be accessed as bits, bytes, and words. SFRs are declared in the same way as other C variable types:
sfr P0 = 0x80; /* Port-0, address 80h */
Generic Pointers/Memory-specific Pointers
Generic pointers are declared in the same fashion as standard C pointers.
int *numptr; /* int ptr */
Specify the memory area in which a generic pointer is stored by using a memory type specifier.
int xdata *numtab; /* ptr to int(s) in xdata */
Download
You can download evaluation development tools for all 8051 and 80251 devices from KEIL:
