Texas Instruments MSP50C6xx manual Sixth file, cmm1ram.asm, allocates memory for cmm1.asm

C– – Efficiency

mov *seconds_passed, a0 inte

mov a0, a0~ ret

The file only has one C–– callable function, getSecondsPassed. The function reads the value in seconds_passed and returns it in A0. All C–– functions have an underscore preceding their name in assembly. The underscore is ignored when programming in C––. In C–– a call to this function would look like

int result = getSecondsPassed();

Notice that the underscore is not used here because C–– is being used instead of assembly. getSecondsPassed() has very simple functionality, but it illustrates several important points. First, interrupts are disabled with the intd instruction. This is extremely important because it is not possible to read the value in seconds_passed and clear it in an atomic operation. If the value is read and the timer fires before it is cleared, one second will be lost. The next important feature to note is the inclusion of rpt2–2 before the intd instruction. Because of pipeline latency, interrupts can still fire for two clock cycles after an intd instruction. The rpt temporarily disables interrupts and ensures that an interrupt does not fire and execute an inte before the intd makes it through the pipeline. Disabling interrupts ensures that the timer will not fire while the value in seconds_passed is being read and altered.

The sixth file, cmm1_ram.asm, allocates memory for cmm1.asm.

;****************************************************************

;CMM1_RAM.IRX

;Start of memory for asmroutines module is defined in

;include ”..\ram\ram.irx” ;****************************************************************

;Variables

;End of memory

RAMEND_CMM1 equ RAMSTART_CMM1

RAMLENGTH_CMM1 equ RAMEND_CMM1 – RAMSTART_CMM1

	In this project, cmm1.asm did not use any RAM, but it can be allocated just like
	the RAM for the ISRs. For example, a variable named tempa could be
	allocated as follows.
; Variables
tempa	equ RAMSTART_CMM1 + 2 * 1

; End of memory RAMEND_CMM1 equ tempa

The last file is the C–– program, main.cmm. This provides all of the top level functionality for the project. Once all of the previous supporting files have been written, writing the C–– program is very much like writing a regular C program.

/****************************************************************

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