nand2/04_Machine_Language

04 Machine Language

leds.asm

To test input and output capability of HACK we will write an endless loop, in which HACK reads the state of the buttons BUT[1:0] and writes the result to LED[1:0]. All devices for input and output are mapped to memory addresses starting from 0x1000. The state of BUT[1:0] can be read at memory address 4097 and the two leds LED[1:0] can be switched on and of by writing to memory address 4096. The Assembler in tools already knows the following predefined symbols.

symbol	value	function
SP	0	stack pointer of VM
LCL	1	local segment of VM
ARG	2	argument of function/method call
THIS	3	pointer to object in heap
THAT	4	pointer to object in heap
R0--R15	0-15	register 0-15
LED	4096	0 LED is off,1 LED is on
BUT	4097	0 BUT pushed down, 1 BUT released up
UART_TX	4098	send byte over UART
UART_RX	4099	receive byte from UART
SPI	4100	read/write to SPI flash rom
SRAM_A	4101	address of SRAM chip for next read/write
SRAM_D	4102	read/write data from/to SRAM chip
GO	4103	switch from BOOT to RUN
LCD8	4104	write 8bit to LCD
LCD16	4105	write 16bit to LCD
RTP	4106	read/write 8bit to RTP
DEBUG0 - DEBUG4	4107 - 4111	reserved for debugging

mult.asm

To test the ALU of HACK we will write a little assembler program, that calculates the multiplication of two integers stored in R0 and R1. The result shoud be stored into R2.

To Test the result we have to load some test values into R0,R1 and R2. After the multiplication is finished we will check the result in R2. To show if the multiplication is correct, we use two strategies:

Use LED to debug

To test mult.asm in real hardware, we can use the LED[1:0] to display if the result is correct or wrong according to:

LED[1:0]	output
00	nothing happened yet
01	start multiplication
10	correct result
11	wrong result

Use DEBUG0-4 register

To test mult.asm in simulation, we can use the DEBUG registers. Every time we change the value of R0--R2 we store the new values also to the corresponding register DEBUG0--DEBUG2. This is done by replacing every instance of a code snippet that changes R1 (and R0,R2 accordingly):

@R1
M=<what so ever>

with the code that additionally writes the new value to the DEBUG1 register:

@R1
DM=<what so ever>
@DEBUG1
M=D

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Project

• Implement leds.asm and mult.asm.

• Put your code in the skeleton file <filename>.asm. To build the .hack binary file, which can than be preloaded to the instruction ROM of HACK in 05_Computer_Architecture/04_HACK, just type:

  $ make leds
  

  or

  $ make mult
  

  This will invoke the assembler and copy the produced binary file ROM.hack in the appropriate folder 05_Computer_Architecture/04_HACK.

• To run the programms you first have to build a HACK computer. This is done in 05_Computer_Architecture.