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Reversed bit order in uart.

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This commit is contained in:
Ross Thompson 2021-11-20 22:42:47 -06:00
parent 3dd83b3113
commit 9d3261ed49
1 changed files with 32 additions and 12 deletions
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44
wally-pipelined/src/uncore/uartPC16550D.sv
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@ -114,6 +114,8 @@ module uartPC16550D(
logic rxdataavailintr, modemstatusintr, intrpending;
logic [2:0] intrID;
logic baudpulseComb;
///////////////////////////////////////////
// Input synchronization: 2-stage synchronizer
///////////////////////////////////////////
@ -135,14 +137,20 @@ module uartPC16550D(
MCR <= #1 5'b0;
LSR <= #1 8'b01100000;
MSR <= #1 4'b0;
DLL <= #1 8'b0;
DLL <= #1 8'd11;
DLM <= #1 8'b0;
SCR <= #1 8'b0; // not strictly necessary to reset
end else begin
if (~MEMWb) begin
case (A)
/* -----\/----- EXCLUDED -----\/-----
3'b000: if (DLAB) DLL <= #1 Din; // else TXHR <= #1 Din; // TX handled in TX register/FIFO section
3'b001: if (DLAB) DLM <= #1 Din; else IER <= #1 Din[3:0];
-----/\----- EXCLUDED -----/\----- */
// *** BUG FIX ME for now for the divider to be 11. Our clock is 10 Mhz. 10Mhz /(11 * 16) = 56818 baud, which is close enough to 57600 baud
3'b000: if (DLAB) DLL <= #1 8'd11; // else TXHR <= #1 Din; // TX handled in TX register/FIFO section
3'b001: if (DLAB) DLM <= #1 8'b0; else IER <= #1 Din[3:0];
3'b010: FCR <= #1 {Din[7:6], 2'b0, Din[3], 2'b0, Din[0]}; // Write only FIFO Control Register; 4:5 reserved and 2:1 self-clearing
3'b011: LCR <= #1 Din;
3'b100: MCR <= #1 Din[4:0];
@ -190,14 +198,26 @@ module uartPC16550D(
// Unlike PC16550D, this unit is hardwired with same rx and tx baud clock
// *** add table of scale factors to get 16x uart clk
///////////////////////////////////////////
// Ross Thompson: Found a bug. If the baud rate dividers DLM, and DLL are reloaded
// the baudcount is not reset to {DLM, DLL, UART_PRESCALE}
always_ff @(posedge HCLK, negedge HRESETn)
if (~HRESETn) begin
baudcount <= #1 0;
baudcount <= #1 1;
baudpulse <= #1 0;
end else if (~MEMWb & DLAB & (A == 3'b0 || A == 3'b1)) begin
baudcount <= #1 '0;
end else begin
baudpulse <= #1 (baudcount == {DLM, DLL, {(`UART_PRESCALE){1'b0}}});
baudcount <= #1 baudpulse ? 0 : baudcount +1;
// the baudpulse is too long by 2 clock cycles.
// This is cause baudpulse is registered adding 1 cycle and
// baudcount is reset when baudcount equals the threshold {DLM, DLL, UART_PRESCALE}
// rather than 1 less than that value. Alternatively the reset value could be 1 rather
// than 0.
baudpulse <= #1 baudpulseComb;
baudcount <= #1 baudpulseComb ? 1 : baudcount +1;
end
assign baudpulseComb = (baudcount == {DLM, DLL, {(`UART_PRESCALE){1'b0}}});
assign txbaudpulse = baudpulse;
assign BAUDOUTb = ~baudpulse;
assign rxbaudpulse = ~RCLK; // usually BAUDOUTb tied to RCLK externally
@ -365,14 +385,14 @@ module uartPC16550D(
endcase
case({LCR[3], LCR[1:0]}) // parity, data bits
// load up start bit (0), 5-8 data bits, 0-1 parity bits, 2 stop bits (only one sometimes used), padding
3'b000: txdata = {1'b0, nexttxdata[4:0], 6'b111111}; // 5 data, no parity
3'b001: txdata = {1'b0, nexttxdata[5:0], 5'b11111}; // 6 data, no parity
3'b010: txdata = {1'b0, nexttxdata[6:0], 4'b1111}; // 7 data, no parity
3'b011: txdata = {1'b0, nexttxdata[7:0], 3'b111}; // 8 data, no parity
3'b100: txdata = {1'b0, nexttxdata[4:0], txparity, 5'b11111}; // 5 data, parity
3'b101: txdata = {1'b0, nexttxdata[5:0], txparity, 4'b1111}; // 6 data, parity
3'b110: txdata = {1'b0, nexttxdata[6:0], txparity, 3'b111}; // 7 data, parity
3'b111: txdata = {1'b0, nexttxdata[7:0], txparity, 2'b11}; // 8 data, parity
3'b000: txdata = {1'b0, nexttxdata[0], nexttxdata[1], nexttxdata[2], nexttxdata[3], nexttxdata[4], 6'b111111}; // 5 data, no parity
3'b001: txdata = {1'b0, nexttxdata[0], nexttxdata[1], nexttxdata[2], nexttxdata[3], nexttxdata[4], nexttxdata[5], 5'b11111}; // 6 data, no parity
3'b010: txdata = {1'b0, nexttxdata[0], nexttxdata[1], nexttxdata[2], nexttxdata[3], nexttxdata[4], nexttxdata[5], nexttxdata[6], 4'b1111}; // 7 data, no parity
3'b011: txdata = {1'b0, nexttxdata[0], nexttxdata[1], nexttxdata[2], nexttxdata[3], nexttxdata[4], nexttxdata[5], nexttxdata[6], nexttxdata[7], 3'b111}; // 8 data, no parity
3'b100: txdata = {1'b0, nexttxdata[0], nexttxdata[1], nexttxdata[2], nexttxdata[3], nexttxdata[4], txparity, 5'b11111}; // 5 data, parity
3'b101: txdata = {1'b0, nexttxdata[0], nexttxdata[1], nexttxdata[2], nexttxdata[3], nexttxdata[4], nexttxdata[5], txparity, 4'b1111}; // 6 data, parity
3'b110: txdata = {1'b0, nexttxdata[0], nexttxdata[1], nexttxdata[2], nexttxdata[3], nexttxdata[4], nexttxdata[5], nexttxdata[6], txparity, 3'b111}; // 7 data, parity
3'b111: txdata = {1'b0, nexttxdata[0], nexttxdata[1], nexttxdata[2], nexttxdata[3], nexttxdata[4], nexttxdata[5], nexttxdata[6], nexttxdata[7], txparity, 2'b11}; // 8 data, parity
endcase
end