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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.
239 lines
4.8 KiB
NASM
239 lines
4.8 KiB
NASM
; *** EEPROM write ***
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; Listen to UART expecting tty-escaped "pingpong" (from tools/) communication.
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;
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; Each of those received bytes is written to the EEPROM, starting at addr 0.
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; that byte is then re-read and sent back to the UART, tty-escaped.
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;
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; Addr selection is done through 2 chained '164, data in/out is done directly
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; with PD7:2 for bits 7:2 and PB1:0 for bits 1:0 (PD1 and PD0 are used for
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; UART).
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;
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; *** Timing, matching and CE ***
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;
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; A lot of trial-and-errors went into those NOPs being place to give time for
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; latching. All these timing are well, well above maximums given in the specs,
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; but when I wasn't going well, well above those specs, I was experiencing
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; read/write errors. It seems we live in an imperfect world!
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;
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; I'm also not sure, in "writedata", whether toggling CE along with WE is
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; actually needed, but until I did, I was experiencing random write failures.
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; So, we end up with this...
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;
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; *** Register Usage ***
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;
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; r0: holds whether last received char was tty-escaped (0 = no, 1=yes)
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; r16: generic tmp
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; r17: generic tmp
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; r20: Byte to send to the "data" SR. Wired to D0-D7.
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; r21: "high" byte, to send to the "addr" SR. Wired to A8-15
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; r22: "low" byte, to send to the "addr" SR. Wired to A0-7
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; r23: tmp value to use for sending to the "addr" SR
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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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; Waits until a char is read, then put it in R20
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; Perform TTY-escape transparently.
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uartrd:
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lds r16, UCSR0A
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sbrs r16, RXC0 ; RXC0 is set? skip rjmp and fetch char.
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rjmp uartrd
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lds r20, UDR0
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; is this the escape char?
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cpi r20, 0x20
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brne uartrd_0
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; escape char
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; We "pong" the escape right away.
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rcall uartwr
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inc r0
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rjmp uartrd
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uartrd_0:
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; should we escape?
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tst r0
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breq uartrd_1
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; yes
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andi r20, 0x7f
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uartrd_1:
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ret
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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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tst r0
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breq uartwr_0
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; we need to escape
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ori r20, 0x80
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clr r0
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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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; send r20 to EEPROM's I/O7:0 through PD7:2 and PB1:0
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writedata:
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cbi PORTB, FLCE
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; addr is latched on WE falling edge
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cbi PORTB, FLWE
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; send bits 7:2
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mov r16, r20
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andi r16, 0xfc
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in r17, PORTD
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andi r17, 0x03
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or r16, r17
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out PORTD, r16
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; send bits 1:0
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mov r16, r20
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andi r16, 0x03
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in r17, PORTB
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andi r17, 0xfc
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or r16, r17
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out PORTB, r16
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; data is latched on rising edge
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sbi PORTB, FLWE
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sbi PORTB, FLCE
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nop ; Give the AT28 time to latch
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nop
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nop
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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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; wait until I/O7 stops toggling
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waitio7:
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cbi PORTB, FLCE
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cbi PORTB, FLOE
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nop ; Give the AT28 time to latch
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nop
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nop
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in r16, PIND
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sbi PORTB, FLOE
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sbi PORTB, FLCE
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andi r16, 0xfc
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cbi PORTB, FLCE
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cbi PORTB, FLOE
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nop ; Give the AT28 time to latch
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nop
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nop
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in r17, PIND
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sbi PORTB, FLOE
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sbi PORTB, FLCE
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andi r17, 0xfc
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cp r16, r17
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brne waitio7
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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 ; Give the AT28 time to latch
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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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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 r0
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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<<RXEN0) | (1<<TXEN0)
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sts UCSR0B, r16
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loop:
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rcall uartrd
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rcall ioout
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rcall nextaddr
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rcall writedata
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rcall ioin
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rcall waitio7
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rcall readdata
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rcall uartwr
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rjmp loop
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