Question

Im writing some C/asm program for the AVR MCU. Im still learning as I go so I hope I have made some sort of mistake in my code.

I have a buffer volatile unsigned char suart_0_rx_buffer[SUART_0_BUF_SIZE+1]; in my C code that I am accessing in my asm code as below. All I want to do is store a byte s0_Rxbyte in the buffer and increment the pointer s0_index every time. ‘s0_Rxbyte` is always a non zero value.

suart_0_wr_buf_2:  ldi     s0_z_low, lo8(suart_0_rx_buffer)
                   ldi     s0_temp1, hi8(suart_0_rx_buffer)
                   add     s0_z_low, s0_index
                   adc     s0_z_high,s0_temp1
suart_0_wr_buf_3:  st      Z+, s0_Rxbyte
                   inc     s0_index
                   clr     s0_temp1
                   st      Z, s0_temp1

If I try and print the contents in a loop in my C code I am getting absolutely nothing.

I didnt want to attach everything here because it will be cluttered.

So does anyone see any problems with the asm code above ?

Answer 1

Managed to figure it out in the end. It was a case of a simple error in the assembly code that caused it write an incorrect location in the SRAM.

suart_0_wr_buf_2:  clr     s0_temp1
                   ldi     s0_z_low, lo8(suart_0_rx_buffer)
                   ldi     s0_z_high, hi8(suart_0_rx_buffer)
                   add     s0_z_low, s0_index
                   adc     s0_z_high, s0_temp1
suart_0_wr_buf_3:  st      Z+, s0_Rxbyte
                   inc     s0_index
                   st      Z, s0_temp1