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https://github.com/hsoft/collapseos.git
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7001446212
Recipes contain bits and pieces of hardware-related knowledge, but these bits feel sparse. I've been wanting to consolidate hardware- related documentation for a while, but always fell at odds with the recipes organisation. We don't have recipes anymore, just a /doc/hw section that contains hardware-related documentation which often translate to precise instructions to run Collapse OS on a specific machine. With this new organisation, I hope to end up with a better, more solid documentation.
140 lines
2.7 KiB
NASM
140 lines
2.7 KiB
NASM
; Use this as a debug companion to at28wr. This simply dumps, TTY-escaped, the
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; contents of the AT28.
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;
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; TODO: not always, but sometimes, the output starts with a spurious 0xFF. But
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; otherwise, the rest of the contents is good, albeit offset by 1 (that is, the
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; byte after the spurious 0xFF is the contents at addr 0). Weird, to fix.
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.include "m328Pdef.inc"
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; *** Pins ***
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.equ SRCP = PORTB2
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.equ SRDS = PORTB1
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.equ FLWE = PORTB3
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.equ FLOE = PORTB4
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.equ FLCE = PORTB5 ; WARNING: same as LED
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; *** Consts ***
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.equ BAUD_PRESCALE = 103 ; 9600 bauds at 16mhz
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rjmp main
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; *** Code ***
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; Sends char in r20 to UART
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; Perform TTY-escape transparently.
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uartwr:
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lds r16, UCSR0A
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sbrs r16, UDRE0 ; wait until send buffer is empty
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rjmp uartwr
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; should we escape?
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cpi r20, 0x21
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brsh uartwr_0 ; r20 >= 0x21, skip
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; escape
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ori r20, 0x80
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ldi r16, 0x20
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sts UDR0, r16
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rjmp uartwr
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uartwr_0:
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sts UDR0, r20
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ret
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; send r23 to addr shift register.
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; We send highest bits first so that Q7 is the MSB and Q0 is the LSB
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sendaddr:
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ldi r16, 8 ; we will loop 8 times
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cbi PORTB, SRDS
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sbrc r23, 7 ; if latest bit isn't cleared, set SER_DP high
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sbi PORTB, SRDS
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; toggle SRCP, not waiting between pulses. The CD74AC164 at 5V has a
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; 5.9ns CP min pulse width. We can't match that at 16mhz. No need to
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; wait.
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cbi PORTB, SRCP
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sbi PORTB, SRCP
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lsl r23 ; shift our data left
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dec r16
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brne sendaddr+1 ; not zero yet? loop! (+1 to avoid reset)
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ret
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; push r20 to the rom and increase the memory counter
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nextaddr:
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; first, set up addr
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mov r23, r21
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rcall sendaddr
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mov r23, r22
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rcall sendaddr
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inc r22
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brne nextaddr_0 ; no overflow? skip
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inc r21
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nextaddr_0:
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ret
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; read EEPROM's I/O7:0 through PD7:2 and PB1:0 into r20
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readdata:
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cbi PORTB, FLCE
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cbi PORTB, FLOE
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nop ; 70ns max delay on at28
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nop
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nop
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nop
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; read bits 7:2
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in r20, PIND
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andi r20, 0xfc
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; read bits 1:0
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in r16, PINB
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andi r16, 0x03
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or r20, r16
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sbi PORTB, FLOE
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sbi PORTB, FLCE
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ret
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; Set PD7:2 and PB1:0 to output
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ioout:
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ldi r16, 0xfc ; PD7:2
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out DDRD, r16
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ldi r16, 0x3f ; PB5:0 (CP, WE, OE and CE too)
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out DDRB, r16
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ret
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; Set PD7:2 and PB1:0 to input
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ioin:
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ldi r16, 0x03 ; PD7:2
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out DDRD, r16
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ldi r16, 0x3c ; PB1:0
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out DDRB, r16
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ret
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main:
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ldi r16, low(RAMEND)
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out SPL, r16
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ldi r16, high(RAMEND)
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out SPH, r16
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; We begin with WE and OE disabled (high), but CE stays enabled (low)
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; the whole time.
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sbi PORTB, FLWE
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sbi PORTB, FLOE
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sbi PORTB, FLCE
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; Clear counters and flags
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clr r21
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clr r22
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; Setup UART
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ldi R16, low(BAUD_PRESCALE)
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sts UBRR0L, r16
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ldi r16, high(BAUD_PRESCALE)
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sts UBRR0H, r16
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ldi r16, (1<<TXEN0)
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sts UCSR0B, r16
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loop:
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rcall ioout
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rcall nextaddr
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rcall ioin
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rcall readdata
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rcall uartwr
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rjmp loop
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